Ogre User Manuel 1 7

OGRE Manual v1.7 (’Cthugha’)

Steve Streeting

Copyright c© Torus Knot Software Ltd

Permission is granted to make and distribute verbatim copies of this manual provided thecopyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the con-ditions for verbatim copying, provided that the entire resulting derived work is distributedunder the terms of a permission notice identical to this one.

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Table of Contents

OGRE Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.1 Object Orientation - more than just a buzzword . . . . . . . . . . . . . . . . 21.2 Multi-everything . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 The Core Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.1 The Root object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.2 The RenderSystem object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.3 The SceneManager object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.4 The ResourceGroupManager Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.5 The Mesh Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.6 Entities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.7 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122.8 Overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3 Scripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.1 Material Scripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.1.1 Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213.1.2 Passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243.1.3 Texture Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453.1.4 Declaring Vertex/Geometry/Fragment Programs . . . . . . . . . . 633.1.5 Cg programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693.1.6 DirectX9 HLSL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703.1.7 OpenGL GLSL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713.1.8 Unified High-level Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763.1.9 Using Vertex/Geometry/Fragment Programs in a Pass . . . . 793.1.10 Vertex Texture Fetch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953.1.11 Script Inheritence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963.1.12 Texture Aliases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003.1.13 Script Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1043.1.14 Script Import Directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

3.2 Compositor Scripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1063.2.1 Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1083.2.2 Target Passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1123.2.3 Compositor Passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1143.2.4 Applying a Compositor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

3.3 Particle Scripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1213.3.1 Particle System Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1233.3.2 Particle Emitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1303.3.3 Particle Emitter Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1313.3.4 Standard Particle Emitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

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3.3.5 Particle Affectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1373.3.6 Standard Particle Affectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

3.4 Overlay Scripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1443.4.1 OverlayElement Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1493.4.2 Standard OverlayElements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

3.5 Font Definition Scripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

4 Mesh Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1584.1 Exporters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1584.2 XmlConverter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1594.3 MeshUpgrader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

5 Hardware Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1605.1 The Hardware Buffer Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1605.2 Buffer Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1605.3 Shadow Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1615.4 Locking buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1625.5 Practical Buffer Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1635.6 Hardware Vertex Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

5.6.1 The VertexData class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1645.6.2 Vertex Declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1645.6.3 Vertex Buffer Bindings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1665.6.4 Updating Vertex Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

5.7 Hardware Index Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1685.7.1 The IndexData class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1685.7.2 Updating Index Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

5.8 Hardware Pixel Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1695.8.1 Textures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1695.8.2 Updating Pixel Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1715.8.3 Texture Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1725.8.4 Pixel Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1735.8.5 Pixel boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

6 External Texture Sources . . . . . . . . . . . . . . . . . . . . 176

7 Shadows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1807.1 Stencil Shadows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1817.2 Texture-based Shadows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1857.3 Modulative Shadows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1907.4 Additive Light Masking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

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8 Animation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1978.1 Skeletal Animation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1978.2 Animation State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1988.3 Vertex Animation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198

8.3.1 Morph Animation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2018.3.2 Pose Animation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2018.3.3 Combining Skeletal and Vertex Animation . . . . . . . . . . . . . . . 202

8.4 SceneNode Animation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2038.5 Numeric Value Animation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

OGRE Manual 1

OGRE Manual

Copyright c© The OGRE Team

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Chapter 1: Introduction 2

1 Introduction

This chapter is intended to give you an overview of the main components of OGRE andwhy they have been put together that way.

1.1 Object Orientation - more than just a buzzword

The name is a dead giveaway. It says Object-Oriented Graphics Rendering Engine, andthat’s exactly what it is. Ok, but why? Why did I choose to make such a big deal aboutthis?

Well, nowadays graphics engines are like any other large software system. They startsmall, but soon they balloon into monstrously complex beasts which just can’t be all un-derstood at once. It’s pretty hard to manage systems of this size, and even harder to makechanges to them reliably, and that’s pretty important in a field where new techniques andapproaches seem to appear every other week. Designing systems around huge files full of Cfunction calls just doesn’t cut it anymore - even if the whole thing is written by one person(not likely) they will find it hard to locate that elusive bit of code after a few months andeven harder to work out how it all fits together.

Object orientation is a very popular approach to addressing the complexity problem.It’s a step up from decomposing your code into separate functions, it groups function andstate data together in classes which are designed to represent real concepts. It allows youto hide complexity inside easily recognised packages with a conceptually simple interface sothey are easy to recognise and have a feel of ’building blocks’ which you can plug togetheragain later. You can also organise these blocks so that some of them look the same onthe outside, but have very different ways of achieving their objectives on the inside, againreducing the complexity for the developers because they only have to learn one interface.

I’m not going to teach you OO here, that’s a subject for many other books, but suffice tosay I’d seen enough benefits of OO in business systems that I was surprised most graphicscode seemed to be written in C function style. I was interested to see whether I could applymy design experience in other types of software to an area which has long held a place inmy heart - 3D graphics engines. Some people I spoke to were of the opinion that usingfull C++ wouldn’t be fast enough for a real-time graphics engine, but others (including me)were of the opinion that, with care, and object-oriented framework can be performant. Wewere right.

In summary, here’s the benefits an object-oriented approach brings to OGRE:

AbstractionCommon interfaces hide the nuances between different implementations of 3DAPI and operating systems


EncapsulationThere is a lot of state management and context-specific actions to be done ina graphics engine - encapsulation allows me to put the code and data nearestto where it is used which makes the code cleaner and easier to understand, andmore reliable because duplication is avoided

PolymorphismThe behaviour of methods changes depending on the type of object you areusing, even if you only learn one interface, e.g. a class specialised for managingindoor levels behaves completely differently from the standard scene manager,but looks identical to other classes in the system and has the same methodscalled on it

1.2 Multi-everything

I wanted to do more than create a 3D engine that ran on one 3D API, on one platform,with one type of scene (indoor levels are most popular). I wanted OGRE to be able toextend to any kind of scene (but yet still implement scene-specific optimisations under thesurface), any platform and any 3D API.

Therefore all the ’visible’ parts of OGRE are completely independent of platform, 3DAPI and scene type. There are no dependencies on Windows types, no assumptions aboutthe type of scene you are creating, and the principles of the 3D aspects are based on coremaths texts rather than one particular API implementation.

Now of course somewhere OGRE has to get down to the nitty-gritty of the specificsof the platform, API and scene, but it does this in subclasses specially designed for theenvironment in question, but which still expose the same interface as the abstract versions.

For example, there is a ’Win32Window’ class which handles all the details about render-ing windows on a Win32 platform - however the application designer only has to manipulateit via the superclass interface ’RenderWindow’, which will be the same across all platforms.

Similarly the ’SceneManager’ class looks after the arrangement of objects in the sceneand their rendering sequence. Applications only have to use this interface, but there is a’BspSceneManager’ class which optimises the scene management for indoor levels, meaningyou get both performance and an easy to learn interface. All applications have to do is hintabout the kind of scene they will be creating and let OGRE choose the most appropriateimplementation - this is covered in a later tutorial.

OGRE’s object-oriented nature makes all this possible. Currently OGRE runs on Win-dows, Linux and Mac OSX using plugins to drive the underlying rendering API (currentlyDirect3D or OpenGL). Applications use OGRE at the abstract level, thus ensuring thatthey automatically operate on all platforms and rendering subsystems that OGRE provides


without any need for platform or API specific code.

Chapter 2: The Core Objects 5

2 The Core Objects

Introduction

This tutorial gives you a quick summary of the core objects that you will use in OGRE andwhat they are used for.

A Word About Namespaces

OGRE uses a C++ feature called namespaces. This lets you put classes, enums, structures,anything really within a ’namespace’ scope which is an easy way to prevent name clashes,i.e. situations where you have 2 things called the same thing. Since OGRE is designed tobe used inside other applications, I wanted to be sure that name clashes would not be aproblem. Some people prefix their classes/types with a short code because some compilersdon’t support namespaces, but I chose to use them because they are the ’right’ way to do it.Sorry if you have a non-compliant compiler, but hey, the C++ standard has been defined foryears, so compiler writers really have no excuse anymore. If your compiler doesn’t supportnamespaces then it’s probably because it’s sh*t - get a better one. ;)

This means every class, type etc should be prefixed with ’Ogre::’, e.g. ’Ogre::Camera’,’Ogre::Vector3’ etc which means if elsewhere in your application you have used a Vector3type you won’t get name clashes. To avoid lots of extra typing you can add a ’usingnamespace Ogre;’ statement to your code which means you don’t have to type the ’Ogre::’prefix unless there is ambiguity (in the situation where you have another definition withthe same name).

Overview from 10,000 feet

Shown below is a diagram of some of the core objects and where they ’sit’ in thegrand scheme of things. This is not all the classes by a long shot, just a few examples


of the more more significant ones to give you an idea of how it slots together.

At the very top of the diagram is the Root object. This is your ’way in’ to the OGREsystem, and it’s where you tend to create the top-level objects that you need to deal with, likescene managers, rendering systems and render windows, loading plugins, all the fundamentalstuff. If you don’t know where to start, Root is it for almost everything, although often itwill just give you another object which will actually do the detail work, since Root itself ismore of an organiser and facilitator object.

The majority of rest of OGRE’s classes fall into one of 3 roles:

Scene ManagementThis is about the contents of your scene, how it’s structured, how it’s viewedfrom cameras, etc. Objects in this area are responsible for giving you a naturaldeclarative interface to the world you’re building; i.e. you don’t tell OGRE "setthese render states and then render 3 polygons", you tell it "I want an objecthere, here and here, with these materials on them, rendered from this view",and let it get on with it.

Resource ManagementAll rendering needs resources, whether it’s geometry, textures, fonts, whatever.It’s important to manage the loading, re-use and unloading of these thingscarefully, so that’s what classes in this area do.

Rendering Finally, there’s getting the visuals on the screen - this is about the lower-levelend of the rendering pipeline, the specific rendering system API objects like


buffers, render states and the like and pushing it all down the pipeline. Classesin the Scene Management subsystem use this to get their higher-level sceneinformation onto the screen.

You’ll notice that scattered around the edge are a number of plugins. OGRE is designedto be extended, and plugins are the usual way to go about it. Many of the classes in OGREcan be subclassed and extended, whether it’s changing the scene organisation through acustom SceneManager, adding a new render system implementation (e.g. Direct3D orOpenGL), or providing a way to load resources from another source (say from a web locationor a database). Again this is just a small smattering of the kinds of things plugins can do,but as you can see they can plug in to almost any aspect of the system. This way, OGREisn’t just a solution for one narrowly defined problem, it can extend to pretty much anythingyou need it to do.

2.1 The Root object

The ’Root’ object is the entry point to the OGRE system. This object MUST be the firstone to be created, and the last one to be destroyed. In the example applications I choseto make an instance of Root a member of my application object which ensured that it wascreated as soon as my application object was, and deleted when the application object wasdeleted.

The root object lets you configure the system, for example through the showConfigDia-log() method which is an extremely handy method which performs all render system optionsdetection and shows a dialog for the user to customise resolution, colour depth, full screenoptions etc. It also sets the options the user selects so that you can initialise the systemdirectly afterwards.

The root object is also your method for obtaining pointers to other objects in the system,such as the SceneManager, RenderSystem and various other resource managers. See belowfor details.

Finally, if you run OGRE in continuous rendering mode, i.e. you want to always refreshall the rendering targets as fast as possible (the norm for games and demos, but not forwindowed utilities), the root object has a method called startRendering, which when calledwill enter a continuous rendering loop which will only end when all rendering windows areclosed, or any FrameListener objects indicate that they want to stop the cycle (see belowfor details of FrameListener objects).

2.2 The RenderSystem object

The RenderSystem object is actually an abstract class which defines the interface to theunderlying 3D API. It is responsible for sending rendering operations to the API and


setting all the various rendering options. This class is abstract because all the imple-mentation is rendering API specific - there are API-specific subclasses for each renderingAPI (e.g. D3DRenderSystem for Direct3D). After the system has been initialised throughRoot::initialise, the RenderSystem object for the selected rendering API is available via theRoot::getRenderSystem() method.

However, a typical application should not normally need to manipulate the RenderSys-tem object directly - everything you need for rendering objects and customising settingsshould be available on the SceneManager, Material and other scene-oriented classes. It’sonly if you want to create multiple rendering windows (completely separate windows in thiscase, not multiple viewports like a split-screen effect which is done via the RenderWindowclass) or access other advanced features that you need access to the RenderSystem object.

For this reason I will not discuss the RenderSystem object further in these tutorials. Youcan assume the SceneManager handles the calls to the RenderSystem at the appropriatetimes.

2.3 The SceneManager object

Apart from the Root object, this is probably the most critical part of the system from theapplication’s point of view. Certainly it will be the object which is most used by the appli-cation. The SceneManager is in charge of the contents of the scene which is to be renderedby the engine. It is responsible for organising the contents using whatever technique itdeems best, for creating and managing all the cameras, movable objects (entities), lightsand materials (surface properties of objects), and for managing the ’world geometry’ whichis the sprawling static geometry usually used to represent the immovable parts of a scene.

It is to the SceneManager that you go when you want to create a camera for the scene.It’s also where you go to retrieve or to remove a light from the scene. There is no need foryour application to keep lists of objects, the SceneManager keeps a named set of all of thescene objects for you to access, should you need them. Look in the main documentationunder the getCamera, getLight, getEntity etc methods.

The SceneManager also sends the scene to the RenderSystem object when it is time torender the scene. You never have to call the SceneManager:: renderScene method directlythough - it is called automatically whenever a rendering target is asked to update.

So most of your interaction with the SceneManager is during scene setup. You’re likely tocall a great number of methods (perhaps driven by some input file containing the scene data)


in order to set up your scene. You can also modify the contents of the scene dynamicallyduring the rendering cycle if you create your own FrameListener object (see later).

Because different scene types require very different algorithmic approaches to decidingwhich objects get sent to the RenderSystem in order to attain good rendering performance,the SceneManager class is designed to be subclassed for different scene types. The defaultSceneManager object will render a scene, but it does little or no scene organisation andyou should not expect the results to be high performance in the case of large scenes. Theintention is that specialisations will be created for each type of scene such that underthe surface the subclass will optimise the scene organisation for best performance givenassumptions which can be made for that scene type. An example is the BspSceneManagerwhich optimises rendering for large indoor levels based on a Binary Space Partition (BSP)tree.

The application using OGRE does not have to know which subclasses are available.The application simply calls Root::createSceneManager(..) passing as a parameter one of anumber of scene types (e.g. ST GENERIC, ST INTERIOR etc). OGRE will automaticallyuse the best SceneManager subclass available for that scene type, or default to the basicSceneManager if a specialist one is not available. This allows the developers of OGRE toadd new scene specialisations later and thus optimise previously unoptimised scene typeswithout the user applications having to change any code.

2.4 The ResourceGroupManager Object

The ResourceGroupManager class is actually a ’hub’ for loading of reusable resources liketextures and meshes. It is the place that you define groups for your resources, so they maybe unloaded and reloaded when you want. Servicing it are a number of ResourceManagerswhich manage the individual types of resource, like TextureManager or MeshManager. Inthis context, resources are sets of data which must be loaded from somewhere to provideOGRE with the data it needs.

ResourceManagers ensure that resources are only loaded once and shared throughoutthe OGRE engine. They also manage the memory requirements of the resources they lookafter. They can also search in a number of locations for the resources they need, includingmultiple search paths and compressed archives (ZIP files).

Most of the time you won’t interact with resource managers directly. Resource managerswill be called by other parts of the OGRE system as required, for example when you requestfor a texture to be added to a Material, the TextureManager will be called for you. If youlike, you can call the appropriate resource manager directly to preload resources (if for


example you want to prevent disk access later on) but most of the time it’s ok to let OGREdecide when to do it.

One thing you will want to do is to tell the resource managers where to look for re-sources. You do this via Root::getSingleton().addResourceLocation, which actually passesthe information on to ResourceGroupManager.

Because there is only ever 1 instance of each resource manager in the engine, if you dowant to get a reference to a resource manager use the following syntax:

TextureManager::getSingleton().someMethod()MeshManager::getSingleton().someMethod()

2.5 The Mesh Object

A Mesh object represents a discrete model, a set of geometry which is self-contained andis typically fairly small on a world scale. Mesh objects are assumed to represent movableobjects and are not used for the sprawling level geometry typically used to create back-grounds.

Mesh objects are a type of resource, and are managed by the MeshManager resourcemanager. They are typically loaded from OGRE’s custom object format, the ’.mesh’ for-mat. Mesh files are typically created by exporting from a modelling tool See Section 4.1[Exporters], page 158 and can be manipulated through various Chapter 4 [Mesh Tools],page 158

You can also create Mesh objects manually by calling the MeshManager::createManualmethod. This way you can define the geometry yourself, but this is outside the scope ofthis manual.

Mesh objects are the basis for the individual movable objects in the world, which arecalled Section 2.6 [Entities], page 11.

Mesh objects can also be animated using See Section 8.1 [Skeletal Animation], page 197.


2.6 Entities

An entity is an instance of a movable object in the scene. It could be a car, a person, adog, a shuriken, whatever. The only assumption is that it does not necessarily have a fixedposition in the world.

Entities are based on discrete meshes, i.e. collections of geometry which are self-containedand typically fairly small on a world scale, which are represented by the Mesh object.Multiple entities can be based on the same mesh, since often you want to create multiplecopies of the same type of object in a scene.

You create an entity by calling the SceneManager::createEntity method, giving it aname and specifying the name of the mesh object which it will be based on (e.g. ’muscle-boundhero.mesh’). The SceneManager will ensure that the mesh is loaded by calling theMeshManager resource manager for you. Only one copy of the Mesh will be loaded.

Entities are not deemed to be a part of the scene until you attach them to a SceneNode(see the section below). By attaching entities to SceneNodes, you can create complex hier-archical relationships between the positions and orientations of entities. You then modifythe positions of the nodes to indirectly affect the entity positions.

When a Mesh is loaded, it automatically comes with a number of materials defined. Itis possible to have more than one material attached to a mesh - different parts of the meshmay use different materials. Any entity created from the mesh will automatically use thedefault materials. However, you can change this on a per-entity basis if you like so you cancreate a number of entities based on the same mesh but with different textures etc.

To understand how this works, you have to know that all Mesh objects are actuallycomposed of SubMesh objects, each of which represents a part of the mesh using oneMaterial. If a Mesh uses only one Material, it will only have one SubMesh.

When an Entity is created based on this Mesh, it is composed of (possibly) multipleSubEntity objects, each matching 1 for 1 with the SubMesh objects from the original Mesh.You can access the SubEntity objects using the Entity::getSubEntity method. Once youhave a reference to a SubEntity, you can change the material it uses by calling it’s setMate-rialName method. In this way you can make an Entity deviate from the default materialsand thus create an individual looking version of it.


2.7 Materials

The Material object controls how objects in the scene are rendered. It specifies what basicsurface properties objects have such as reflectance of colours, shininess etc, how manytexture layers are present, what images are on them and how they are blended together,what special effects are applied such as environment mapping, what culling mode is used,how the textures are filtered etc.

Materials can either be set up programmatically, by calling SceneMan-ager::createMaterial and tweaking the settings, or by specifying it in a ’script’ which isloaded at runtime. See Section 3.1 [Material Scripts], page 16 for more info.

Basically everything about the appearance of an object apart from it’s shape is controlledby the Material class.

The SceneManager class manages the master list of materials available to the scene.The list can be added to by the application by calling SceneManager::createMaterial, orby loading a Mesh (which will in turn load material properties). Whenever materials areadded to the SceneManager, they start off with a default set of properties; these are definedby OGRE as the following:

• ambient reflectance = ColourValue::White (full)• diffuse reflectance = ColourValue::White (full)• specular reflectance = ColourValue::Black (none)• emmissive = ColourValue::Black (none)• shininess = 0 (not shiny)• No texture layers (& hence no textures)• SourceBlendFactor = SBF ONE, DestBlendFactor = SBF ZERO (opaque)• Depth buffer checking on• Depth buffer writing on• Depth buffer comparison function = CMPF LESS EQUAL• Culling mode = CULL CLOCKWISE• Ambient lighting in scene = ColourValue(0.5, 0.5, 0.5) (mid-grey)• Dynamic lighting enabled• Gourad shading mode• Solid polygon mode• Bilinear texture filtering

You can alter these settings by calling SceneManager::getDefaultMaterialSettings() andmaking the required changes to the Material which is returned.


Entities automatically have Material’s associated with them if they use a Mesh object,since the Mesh object typically sets up it’s required materials on loading. You can alsocustomise the material used by an entity as described in Section 2.6 [Entities], page 11.Just create a new Material, set it up how you like (you can copy an existing material intoit if you like using a standard assignment statement) and point the SubEntity entries at itusing SubEntity::setMaterialName().

2.8 Overlays

Overlays allow you to render 2D and 3D elements on top of the normal scene contents tocreate effects like heads-up displays (HUDs), menu systems, status panels etc. The framerate statistics panel which comes as standard with OGRE is an example of an overlay.Overlays can contain 2D or 3D elements. 2D elements are used for HUDs, and 3D elementscan be used to create cockpits or any other 3D object which you wish to be rendered ontop of the rest of the scene.

You can create overlays either through the SceneManager::createOverlay method, or youcan define them in an .overlay script. In reality the latter is likely to be the most practicalbecause it is easier to tweak (without the need to recompile the code). Note that you candefine as many overlays as you like: they all start off life hidden, and you display them bycalling their ’show()’ method. You can also show multiple overlays at once, and their Zorder is determined by the Overlay::setZOrder() method.

Creating 2D Elements

The OverlayElement class abstracts the details of 2D elements which are added to overlays.All items which can be added to overlays are derived from this class. It is possible (andencouraged) for users of OGRE to define their own custom subclasses of OverlayElement inorder to provide their own user controls. The key common features of all OverlayElementsare things like size, position, basic material name etc. Subclasses extend this behaviour toinclude more complex properties and behaviour.

An important built-in subclass of OverlayElement is OverlayContainer. OverlayCon-tainer is the same as a OverlayElement, except that it can contain other OverlayElements,grouping them together (allowing them to be moved together for example) and providingthem with a local coordinate origin for easier lineup.

The third important class is OverlayManager. Whenever an application wishes tocreate a 2D element to add to an overlay (or a container), it should call OverlayMan-ager::createOverlayElement. The type of element you wish to create is identified by astring, the reason being that it allows plugins to register new types of OverlayElement foryou to create without you having to link specifically to those libraries. For example, to cre-


ate a panel (a plain rectangular area which can contain other OverlayElements) you wouldcall OverlayManager::getSingleton().createOverlayElement("Panel", "myNewPanel");

Adding 2D Elements to the Overlay

Only OverlayContainers can be added direct to an overlay. The reason is that each levelof container establishes the Zorder of the elements contained within it, so if you nest sev-eral containers, inner containers have a higher Zorder than outer ones to ensure they aredisplayed correctly. To add a container (such as a Panel) to the overlay, simply call Over-lay::add2D.

If you wish to add child elements to that container, call OverlayContainer::addChild.Child elements can be OverlayElements or OverlayContainer instances themselves. Re-member that the position of a child element is relative to the top-left corner of it’s parent.

A word about 2D coordinates

OGRE allows you to place and size elements based on 2 coordinate systems: relative andpixel based.

Pixel ModeThis mode is useful when you want to specify an exact size for your overlayitems, and you don’t mind if those items get smaller on the screen if you increasethe screen resolution (in fact you might want this). In this mode the only wayto put something in the middle or at the right or bottom of the screen reliablyin any resolution is to use the aligning options, whilst in relative mode you cando it just by using the right relative coordinates. This mode is very simple, thetop-left of the screen is (0,0) and the bottom-right of the screen depends onthe resolution. As mentioned above, you can use the aligning options to makethe horizontal and vertical coordinate origins the right, bottom or center of thescreen if you want to place pixel items in these locations without knowing theresolution.

Relative ModeThis mode is useful when you want items in the overlay to be the same size onthe screen no matter what the resolution. In relative mode, the top-left of thescreen is (0,0) and the bottom-right is (1,1). So if you place an element at (0.5,0.5), it’s top-left corner is placed exactly in the center of the screen, no matterwhat resolution the application is running in. The same principle applies tosizes; if you set the width of an element to 0.5, it covers half the width of thescreen. Note that because the aspect ratio of the screen is typically 1.3333 : 1(width : height), an element with dimensions (0.25, 0.25) will not be square,but it will take up exactly 1/16th of the screen in area terms. If you want


square-looking areas you will have to compensate using the typical aspect ratioe.g. use (0.1875, 0.25) instead.

Transforming Overlays

Another nice feature of overlays is being able to rotate, scroll and scale them as a whole.You can use this for zooming in / out menu systems, dropping them in from off screen andother nice effects. See the Overlay::scroll, Overlay::rotate and Overlay::scale methods formore information.

Scripting overlays

Overlays can also be defined in scripts. See Section 3.4 [Overlay Scripts], page 144 fordetails.

GUI systems

Overlays are only really designed for non-interactive screen elements, although you canuse them as a crude GUI. For a far more complete GUI solution, we recommend CEGui(http://www.cegui.org.uk), as demonstrated in the sample Demo Gui.

http://www.cegui.org.uk

Chapter 3: Scripts 16

3 Scripts

OGRE drives many of its features through scripts in order to make it easier to set up.The scripts are simply plain text files which can be edited in any standard text editor, andmodifying them immediately takes effect on your OGRE-based applications, without anyneed to recompile. This makes prototyping a lot faster. Here are the items that OGRE letsyou script:

• Section 3.1 [Material Scripts], page 16

• Section 3.2 [Compositor Scripts], page 106

• Section 3.3 [Particle Scripts], page 121

• Section 3.4 [Overlay Scripts], page 144

• Section 3.5 [Font Definition Scripts], page 155

3.1 Material Scripts

Material scripts offer you the ability to define complex materials in a script which can bereused easily. Whilst you could set up all materials for a scene in code using the methodsof the Material and TextureLayer classes, in practice it’s a bit unwieldy. Instead you canstore material definitions in text files which can then be loaded whenever required.

Loading scripts

Material scripts are loaded when resource groups are initialised: OGRE looks in all re-source locations associated with the group (see Root::addResourceLocation) for files withthe ’.material’ extension and parses them. If you want to parse files manually, use Materi-alSerializer::parseScript.

It’s important to realise that materials are not loaded completely by this parsing process:only the definition is loaded, no textures or other resources are loaded. This is because it iscommon to have a large library of materials, but only use a relatively small subset of themin any one scene. To load every material completely in every script would therefore causeunnecessary memory overhead. You can access a ’deferred load’ Material in the normalway (MaterialManager::getSingleton().getByName()), but you must call the ’load’ methodbefore trying to use it. Ogre does this for you when using the normal material assignmentmethods of entities etc.

Another important factor is that material names must be unique throughout ALL scriptsloaded by the system, since materials are always identified by name.


Format

Several materials may be defined in a single script. The script format is pseudo-C++, withsections delimited by curly braces (’’, ’’), and comments indicated by starting a line with’//’ (note, no nested form comments allowed). The general format is shown below in theexample below (note that to start with, we only consider fixed-function materials whichdon’t use vertex, geometry or fragment programs, these are covered later):

// This is a commentmaterial walls/funkywall1{

// first, preferred techniquetechnique{

// first passpass{

ambient 0.5 0.5 0.5diffuse 1.0 1.0 1.0

// Texture unit 0texture_unit{

texture wibbly.jpgscroll_anim 0.1 0.0wave_xform scale sine 0.0 0.7 0.0 1.0

}// Texture unit 1 (this is a multitexture pass)texture_unit{

texture wobbly.pngrotate_anim 0.25colour_op add

}}

}

// Second technique, can be used as a fallback or LOD leveltechnique{

// .. and so on}

}

Every material in the script must be given a name, which is the line ’material <blah>’before the first opening ’’. This name must be globally unique. It can include path characters


(as in the example) to logically divide up your materials, and also to avoid duplicate names,but the engine does not treat the name as hierarchical, just as a string. If you includespaces in the name, it must be enclosed in double quotes.

NOTE: ’:’ is the delimiter for specifying material copy in the script so it can’t be usedas part of the material name.

A material can inherit from a previously defined material by using a colon : after thematerial name followed by the name of the reference material to inherit from. You can infact even inherit just parts of a material from others; all this is covered in See Section 3.1.11[Script Inheritence], page 96). You can also use variables in your script which can bereplaced in inheriting versions, see See Section 3.1.13 [Script Variables], page 104.

A material can be made up of many techniques (See Section 3.1.1 [Techniques], page 21)-a technique is one way of achieving the effect you are looking for. You can supply more thanone technique in order to provide fallback approaches where a card does not have the abilityto render the preferred technique, or where you wish to define lower level of detail versionsof the material in order to conserve rendering power when objects are more distant.

Each technique can be made up of many passes (See Section 3.1.2 [Passes], page 24), thatis a complete render of the object can be performed multiple times with different settingsin order to produce composite effects. Ogre may also split the passes you have definedinto many passes at runtime, if you define a pass which uses too many texture units forthe card you are currently running on (note that it can only do this if you are not using afragment program). Each pass has a number of top-level attributes such as ’ambient’ to setthe amount & colour of the ambient light reflected by the material. Some of these optionsdo not apply if you are using vertex programs, See Section 3.1.2 [Passes], page 24 for moredetails.

Within each pass, there can be zero or many texture units in use (See Section 3.1.3[Texture Units], page 45). These define the texture to be used, and optionally some blendingoperations (which use multitexturing) and texture effects.

You can also reference vertex and fragment programs (or vertex and pixel shaders, ifyou want to use that terminology) in a pass with a given set of parameters. Programsthemselves are declared in separate .program scripts (See Section 3.1.4 [Declaring Ver-tex/Geometry/Fragment Programs], page 63) and are used as described in Section 3.1.9[Using Vertex/Geometry/Fragment Programs in a Pass], page 79.


Top-level material attributes

The outermost section of a material definition does not have a lot of attributes of its own(most of the configurable parameters are within the child sections. However, it does havesome, and here they are:

lod distances (deprecated)

This option is deprecated in favour of 〈undefined〉 [lod values], page 〈undefined〉 now.

lod strategy

Sets the name of the LOD strategy to use. Defaults to ’Distance’ which means LOD changesbased on distance from the camera. Also supported is ’PixelCount’ which changes LODbased on an estimate of the screen-space pixels affected.

Format: lod strategy <name>Default: lod strategy Distance

lod values

This attribute defines the values used to control the LOD transition for this material. Bysetting this attribute, you indicate that you want this material to alter the Technique thatit uses based on some metric, such as the distance from the camera, or the approximatescreen space coverage. The exact meaning of these values is determined by the option youselect for [lod strategy], page 19 - it is a list of distances for the ’Distance’ strategy, anda list of pixel counts for the ’PixelCount’ strategy, for example. You must give it a list ofvalues, in order from highest LOD value to lowest LOD value, each one indicating the pointat which the material will switch to the next LOD. Implicitly, all materials activate LODindex 0 for values less than the first entry, so you do not have to specify ’0’ at the start ofthe list. You must ensure that there is at least one Technique with a [lod index], page 22value for each value in the list (so if you specify 3 values, you must have techniques for LODindexes 0, 1, 2 and 3). Note you must always have at least one Technique at lod index 0.

Format: lod values <value0> <value1> <value2> ...Default: none

Example:lod strategy Distance lod values 300.0 600.5 1200


The above example would cause the material to use the best Technique at lod index 0up to a distance of 300 world units, the best from lod index 1 from 300 up to 600, lod index2 from 600 to 1200, and lod index 3 from 1200 upwards.

receive shadows

This attribute controls whether objects using this material can have shadows cast uponthem.

Format: receive shadows <on|off>Default: on

Whether or not an object receives a shadow is the combination of a number of factors,See Chapter 7 [Shadows], page 180 for full details; however this allows you to make amaterial opt-out of receiving shadows if required. Note that transparent materials neverreceive shadows so this option only has an effect on solid materials.

transparency casts shadows

This attribute controls whether transparent materials can cast certain kinds of shadow.

Format: transparency casts shadows <on|off>Default: off

Whether or not an object casts a shadow is the combination of a number of factors, SeeChapter 7 [Shadows], page 180 for full details; however this allows you to make a transparentmaterial cast shadows, when it would otherwise not. For example, when using textureshadows, transparent materials are normally not rendered into the shadow texture becausethey should not block light. This flag overrides that.

set texture alias

This attribute associates a texture alias with a texture name.

Format: set texture alias <alias name> <texture name>

This attribute can be used to set the textures used in texture unit states that wereinherited from another material.(See Section 3.1.12 [Texture Aliases], page 100)


3.1.1 Techniques

A "technique" section in your material script encapsulates a single method of rendering anobject. The simplest of material definitions only contains a single technique, however sincePC hardware varies quite greatly in it’s capabilities, you can only do this if you are surethat every card for which you intend to target your application will support the capabilitieswhich your technique requires. In addition, it can be useful to define simpler ways to rendera material if you wish to use material LOD, such that more distant objects use a simpler,less performance-hungry technique.

When a material is used for the first time, it is ’compiled’. That involves scanning thetechniques which have been defined, and marking which of them are supportable using thecurrent rendering API and graphics card. If no techniques are supportable, your materialwill render as blank white. The compilation examines a number of things, such as:• The number of texture unit entries in each pass

Note that if the number of texture unit entries exceeds the number of texture units inthe current graphics card, the technique may still be supportable so long as a fragmentprogram is not being used. In this case, Ogre will split the pass which has too manyentries into multiple passes for the less capable card, and the multitexture blend willbe turned into a multipass blend (See [colour op multipass fallback], page 58).

• Whether vertex, geometry or fragment programs are used, and if so which syntax theyuse (e.g. vs 1 1, ps 2 x, arbfp1 etc.)

• Other effects like cube mapping and dot3 blending• Whether the vendor or device name of the current graphics card matches some user-

specified rules

In a material script, techniques must be listed in order of preference, i.e. the earlier tech-niques are preferred over the later techniques. This normally means you will list your mostadvanced, most demanding techniques first in the script, and list fallbacks afterwards.

To help clearly identify what each technique is used for, the technique can be namedbut its optional. Techniques not named within the script will take on a name that is thetechnique index number. For example: the first technique in a material is index 0, its namewould be "0" if it was not given a name in the script. The technique name must be uniquewithin the material or else the final technique is the resulting merge of all techniques withthe same name in the material. A warning message is posted in the Ogre.log if this occurs.Named techniques can help when inheriting a material and modifying an existing technique:(See Section 3.1.11 [Script Inheritence], page 96)

Format: technique name

Techniques have only a small number of attributes of their own:


• [scheme], page 22• [lod index], page 22 (and also see [lod distances], page 19 in the parent material)• [shadow caster material], page 23• [shadow receiver material], page 23• [gpu vendor rule], page 23• [gpu device rule], page 23

scheme

Sets the ’scheme’ this Technique belongs to. Material schemes are used to control top-level switching from one set of techniques to another. For example, you might use thisto define ’high’, ’medium’ and ’low’ complexity levels on materials to allow a user to picka performance / quality ratio. Another possibility is that you have a fully HDR-enabledpipeline for top machines, rendering all objects using unclamped shaders, and a simplerpipeline for others; this can be implemented using schemes. The active scheme is typicallycontrolled at a viewport level, and the active one defaults to ’Default’.

Format: scheme <name>Example: scheme hdrDefault: scheme Default

lod index

Sets the level-of-detail (LOD) index this Technique belongs to.

Format: lod index <number>NB Valid values are 0 (highest level of detail) to 65535, although this is unlikely. You shouldnot leave gaps in the LOD indexes between Techniques.

Example: lod index 1

All techniques must belong to a LOD index, by default they all belong to index 0, i.e.the highest LOD. Increasing indexes denote lower levels of detail. You can (and often will)assign more than one technique to the same LOD index, what this means is that OGREwill pick the best technique of the ones listed at the same LOD index. For readability, it isadvised that you list your techniques in order of LOD, then in order of preference, althoughthe latter is the only prerequisite (OGRE determines which one is ’best’ by which one islisted first). You must always have at least one Technique at lod index 0.

The distance at which a LOD level is applied is determined by the lod distances attributeof the containing material, See [lod distances], page 19 for details.


Default: lod index 0

Techniques also contain one or more passes (and there must be at least one), SeeSection 3.1.2 [Passes], page 24.

shadow caster material

When using See Section 7.2 [Texture-based Shadows], page 185 you can specify an alternatematerial to use when rendering the object using this material into the shadow texture. Thisis like a more advanced version of using shadow caster vertex program, however note thatfor the moment you are expected to render the shadow in one pass, i.e. only the first passis respected.

shadow receiver material

When using See Section 7.2 [Texture-based Shadows], page 185 you can specify an alternatematerial to use when performing the receiver shadow pass. Note that this explicit ’receiver’pass is only done when you’re not using [Integrated Texture Shadows], page 189 - i.e.the shadow rendering is done separately (either as a modulative pass, or a masked lightpass). This is like a more advanced version of using shadow receiver vertex program andshadow receiver fragment program, however note that for the moment you are expected torender the shadow in one pass, i.e. only the first pass is respected.

gpu vendor rule and gpu device rule

Although Ogre does a good job of detecting the capabilities of graphics cards and settingthe supportability of techniques from that, occasionally card-specific behaviour exists whichis not necessarily detectable and you may want to ensure that your materials go down aparticular path to either use or avoid that behaviour. This is what these rules are for -you can specify matching rules so that a technique will be considered supportable only oncards from a particular vendor, or which match a device name pattern, or will be consideredsupported only if they don’t fulfill such matches.

The format of the rules are as follows:

gpu vendor rule <include|exclude> <vendor name>gpu device rule <include|exclude> <device pattern> [case sensitive]

An ’include’ rule means that the technique will only be supported if one of the include rulesis matched (if no include rules are provided, anything will pass). An ’exclude’ rules meansthat the technique is considered unsupported if any of the exclude rules are matched. Youcan provide as many rules as you like, although <vendor name> and <device pattern> mustobviously be unique. The valid list of <vendor name> values is currently ’nvidia’, ’ati’,’intel’, ’s3’, ’matrox’ and ’3dlabs’. <device pattern> can be any string, and you can usewildcards (’*’) if you need to match variants. Here’s an example:


gpu vendor rule include nvidiagpu vendor rule include intelgpu device rule exclude *950*

These rules, if all included in one technique, will mean that the technique will only beconsidered supported on graphics cards made by NVIDIA and Intel, and so long as thedevice name doesn’t have ’950’ in it.

Note that these rules can only mark a technique ’unsupported’ when it would otherwisebe considered ’supported’ judging by the hardware capabilities. Even if a technique passesthese rules, it is still subject to the usual hardware support tests.

3.1.2 Passes

A pass is a single render of the geometry in question; a single call to the rendering APIwith a certain set of rendering properties. A technique can have between one and 16 passes,although clearly the more passes you use, the more expensive the technique will be to render.

To help clearly identify what each pass is used for, the pass can be named but its optional.Passes not named within the script will take on a name that is the pass index number. Forexample: the first pass in a technique is index 0 so its name would be "0" if it was not givena name in the script. The pass name must be unique within the technique or else the finalpass is the resulting merge of all passes with the same name in the technique. A warningmessage is posted in the Ogre.log if this occurs. Named passes can help when inheriting amaterial and modifying an existing pass: (See Section 3.1.11 [Script Inheritence], page 96)

Passes have a set of global attributes (described below), zero or more nested texture unitentries (See Section 3.1.3 [Texture Units], page 45), and optionally a reference to a vertex and/ or a fragment program (See Section 3.1.9 [Using Vertex/Geometry/Fragment Programsin a Pass], page 79).

Here are the attributes you can use in a ’pass’ section of a .material script:• [ambient], page 25• [diffuse], page 26• [specular], page 26• [emissive], page 27• [scene blend], page 28• [separate scene blend], page 29• [scene blend op], page 30


• [separate scene blend op], page 30• [depth check], page 30• [depth write], page 31• [depth func], page 31• [depth bias], page 32• [iteration depth bias], page 32• [alpha rejection], page 32• [alpha to coverage], page 33• [light scissor], page 33• [light clip planes], page 34• [illumination stage], page 35• [transparent sorting], page 35• [normalise normals], page 35• [cull hardware], page 36• [cull software], page 36• [lighting], page 37• [shading], page 37• [polygon mode], page 38• [polygon mode overrideable], page 38• [fog override], page 39• [colour write], page 39• [max lights], page 40• [start light], page 40• [iteration], page 41• [point size], page 44• [point sprites], page 44• [point size attenuation], page 45• [point size min], page 45• [point size max], page 45

Attribute Descriptions

ambient

Sets the ambient colour reflectance properties of this pass. This attribute has no effect if aasm, CG, or HLSL shader program is used. With GLSL, the shader can read the OpenGLmaterial state.

Format: ambient (<red> <green> <blue> [<alpha>]| vertexcolour)NB valid colour values are between 0.0 and 1.0.


Example: ambient 0.0 0.8 0.0

The base colour of a pass is determined by how much red, green and blue light is reflectsat each vertex. This property determines how much ambient light (directionless global light)is reflected. It is also possible to make the ambient reflectance track the vertex colour asdefined in the mesh by using the keyword vertexcolour instead of the colour values. Thedefault is full white, meaning objects are completely globally illuminated. Reduce this ifyou want to see diffuse or specular light effects, or change the blend of colours to make theobject have a base colour other than white. This setting has no effect if dynamic lighting isdisabled using the ’lighting off’ attribute, or if any texture layer has a ’colour op replace’attribute.

Default: ambient 1.0 1.0 1.0 1.0

diffuse

Sets the diffuse colour reflectance properties of this pass. This attribute has no effect if aasm, CG, or HLSL shader program is used. With GLSL, the shader can read the OpenGLmaterial state.

Format: diffuse (<red> <green> <blue> [<alpha>]| vertexcolour)NB valid colour values are between 0.0 and 1.0.

Example: diffuse 1.0 0.5 0.5

The base colour of a pass is determined by how much red, green and blue light is reflectsat each vertex. This property determines how much diffuse light (light from instances ofthe Light class in the scene) is reflected. It is also possible to make the diffuse reflectancetrack the vertex colour as defined in the mesh by using the keyword vertexcolour insteadof the colour values. The default is full white, meaning objects reflect the maximum whitelight they can from Light objects. This setting has no effect if dynamic lighting is disabledusing the ’lighting off’ attribute, or if any texture layer has a ’colour op replace’ attribute.

Default: diffuse 1.0 1.0 1.0 1.0


specular

Sets the specular colour reflectance properties of this pass. This attribute has no effect if aasm, CG, or HLSL shader program is used. With GLSL, the shader can read the OpenGLmaterial state.

Format: specular (<red> <green> <blue> [<alpha>]| vertexcolour) <shininess>NB valid colour values are between 0.0 and 1.0. Shininess can be any value greater than 0.

Example: specular 1.0 1.0 1.0 12.5

The base colour of a pass is determined by how much red, green and blue light is reflectsat each vertex. This property determines how much specular light (highlights from instancesof the Light class in the scene) is reflected. It is also possible to make the diffuse reflectancetrack the vertex colour as defined in the mesh by using the keyword vertexcolour insteadof the colour values. The default is to reflect no specular light. The colour of the specularhighlights is determined by the colour parameters, and the size of the highlights by theseparate shininess parameter.. The higher the value of the shininess parameter, the sharperthe highlight ie the radius is smaller. Beware of using shininess values in the range of 0 to1 since this causes the the specular colour to be applied to the whole surface that has thematerial applied to it. When the viewing angle to the surface changes, ugly flickering willalso occur when shininess is in the range of 0 to 1. Shininess values between 1 and 128 workbest in both DirectX and OpenGL renderers. This setting has no effect if dynamic lightingis disabled using the ’lighting off’ attribute, or if any texture layer has a ’colour op replace’attribute.

Default: specular 0.0 0.0 0.0 0.0 0.0

emissive

Sets the amount of self-illumination an object has. This attribute has no effect if a asm, CG,or HLSL shader program is used. With GLSL, the shader can read the OpenGL materialstate.

Format: emissive (<red> <green> <blue> [<alpha>]| vertexcolour)NB valid colour values are between 0.0 and 1.0.


Example: emissive 1.0 0.0 0.0

If an object is self-illuminating, it does not need external sources to light it, ambientor otherwise. It’s like the object has it’s own personal ambient light. Unlike the namesuggests, this object doesn’t act as a light source for other objects in the scene (if you wantit to, you have to create a light which is centered on the object). It is also possible to makethe emissive colour track the vertex colour as defined in the mesh by using the keywordvertexcolour instead of the colour values. This setting has no effect if dynamic lighting isdisabled using the ’lighting off’ attribute, or if any texture layer has a ’colour op replace’attribute.

Default: emissive 0.0 0.0 0.0 0.0

scene blend

Sets the kind of blending this pass has with the existing contents of the scene. Wheras thetexture blending operations seen in the texture unit entries are concerned with blendingbetween texture layers, this blending is about combining the output of this pass as a wholewith the existing contents of the rendering target. This blending therefore allows objecttransparency and other special effects. There are 2 formats, one using predefined blendtypes, the other allowing a roll-your-own approach using source and destination factors.

Format1: scene blend <add|modulate|alpha blend|colour blend>

Example: scene blend add

This is the simpler form, where the most commonly used blending modes are enumeratedusing a single parameter. Valid <blend type> parameters are:

add The colour of the rendering output is added to the scene. Good for explosions,flares, lights, ghosts etc. Equivalent to ’scene blend one one’.

modulate The colour of the rendering output is multiplied with the scene contents. Gen-erally colours and darkens the scene, good for smoked glass, semi-transparentobjects etc. Equivalent to ’scene blend dest colour zero’.

colour blendColour the scene based on the brightness of the input colours, but don’t darken.Equivalent to ’scene blend src colour one minus src colour’

alpha blendThe alpha value of the rendering output is used as a mask. Equivalent to’scene blend src alpha one minus src alpha’


Format2: scene blend <src factor> <dest factor>

Example: scene blend one one minus dest alpha

This version of the method allows complete control over the blending operation, byspecifying the source and destination blending factors. The resulting colour which is writtento the rendering target is (texture * sourceFactor) + (scene pixel * destFactor). Valid valuesfor both parameters are:

one Constant value of 1.0

zero Constant value of 0.0

dest colourThe existing pixel colour

src colour The texture pixel (texel) colour

one minus dest colour1 - (dest colour)

one minus src colour1 - (src colour)

dest alpha The existing pixel alpha value

src alpha The texel alpha value

one minus dest alpha1 - (dest alpha)

one minus src alpha1 - (src alpha)

Default: scene blend one zero (opaque)

Also see [separate scene blend], page 29.

separate scene blend

This option operates in exactly the same way as [scene blend], page 28, except that it allowsyou to specify the operations to perform between the rendered pixel and the frame bufferseparately for colour and alpha components. By nature this option is only useful whenrendering to targets which have an alpha channel which you’ll use for later processing, suchas a render texture.

Format1: separate scene blend <simple colour blend> <simple alpha blend>


Example: separate scene blend add modulate

This example would add colour components but multiply alpha components. The blendmodes available are as in [scene blend], page 28. The more advanced form is also available:

Format2: separate scene blend <colour src factor> <colour dest factor> <al-pha src factor> <alpha dest factor>

Example: separate scene blend one one minus dest alpha one one

Again the options available in the second format are the same as those in the secondformat of [scene blend], page 28.

scene blend op

This directive changes the operation which is applied between the two components of thescene blending equation, which by default is ’add’ (sourceFactor * source + destFactor *dest). You may change this to ’add’, ’subtract’, ’reverse subtract’, ’min’ or ’max’.

Format: scene blend op <add|subtract|reverse subtract|min|max>

Default: scene blend op add

separate scene blend op

This directive is as scene blend op, except that you can set the operation for colour andalpha separately.

Format: separate scene blend op <colourOp> <alphaOp>

Default: separate scene blend op add add

depth check

Sets whether or not this pass renders with depth-buffer checking on or not.

Format: depth check <on|off>


If depth-buffer checking is on, whenever a pixel is about to be written to the framebuffer the depth buffer is checked to see if the pixel is in front of all other pixels written atthat point. If not, the pixel is not written. If depth checking is off, pixels are written nomatter what has been rendered before. Also see depth func for more advanced depth checkconfiguration.

Default: depth check on

depth write

Sets whether or not this pass renders with depth-buffer writing on or not.

Format: depth write <on|off>

If depth-buffer writing is on, whenever a pixel is written to the frame buffer the depthbuffer is updated with the depth value of that new pixel, thus affecting future renderingoperations if future pixels are behind this one. If depth writing is off, pixels are writtenwithout updating the depth buffer. Depth writing should normally be on but can be turnedoff when rendering static backgrounds or when rendering a collection of transparent objectsat the end of a scene so that they overlap each other correctly.

Default: depth write on

depth func

Sets the function used to compare depth values when depth checking is on.

Format: depth func <func>

If depth checking is enabled (see depth check) a comparison occurs between the depthvalue of the pixel to be written and the current contents of the buffer. This comparison isnormally less equal, i.e. the pixel is written if it is closer (or at the same distance) than thecurrent contents. The possible functions are:

always failNever writes a pixel to the render target

always passAlways writes a pixel to the render target

less Write if (new Z < existing Z)


less equal Write if (new Z <= existing Z)

equal Write if (new Z == existing Z)

not equal Write if (new Z != existing Z)

greater equalWrite if (new Z >= existing Z)

greater Write if (new Z >existing Z)

Default: depth func less equal

depth bias

Sets the bias applied to the depth value of this pass. Can be used to make coplanar polygonsappear on top of others e.g. for decals.

Format: depth bias <constant bias> [<slopescale bias>]

The final depth bias value is constant bias * minObservableDepth + maxSlope *slopescale bias. Slope scale biasing is relative to the angle of the polygon to the camera,which makes for a more appropriate bias value, but this is ignored on some older hardware.Constant biasing is expressed as a factor of the minimum depth value, so a value of 1 willnudge the depth by one ’notch’ if you will. Also see [iteration depth bias], page 32

iteration depth bias

Sets an additional bias derived from the number of times a given pass has been iterated.Operates just like [depth bias], page 32 except that it applies an additional bias factorto the base depth bias value, multiplying the provided value by the number of times thispass has been iterated before, through one of the [iteration], page 41 variants. So thefirst time the pass will get the depth bias value, the second time it will get depth bias +iteration depth bias, the third time it will get depth bias + iteration depth bias * 2, andso on. The default is zero.

Format: iteration depth bias <bias per iteration>


alpha rejection

Sets the way the pass will have use alpha to totally reject pixels from the pipeline.

Format: alpha rejection <function> <value>

Example: alpha rejection greater equal 128

The function parameter can be any of the options listed in the material depth functionattribute. The value parameter can theoretically be any value between 0 and 255, but isbest limited to 0 or 128 for hardware compatibility.

Default: alpha rejection always pass

alpha to coverage

Sets whether this pass will use ’alpha to coverage’, a way to multisample alpha textureedges so they blend more seamlessly with the background. This facility is typically onlyavailable on cards from around 2006 onwards, but it is safe to enable it anyway - Ogre willjust ignore it if the hardware does not support it. The common use for alpha to coverageis foliage rendering and chain-link fence style textures.

Format: alpha to coverage <on|off>

Default: alpha to coverage off

light scissor

Sets whether when rendering this pass, rendering will be limited to a screen-space scissorrectangle representing the coverage of the light(s) being used in this pass, derived from theirattenuation ranges.

Format: light scissor <on|off>

Default: light scissor off


This option is usually only useful if this pass is an additive lighting pass, and is at leastthe second one in the technique. Ie areas which are not affected by the current light(s) willnever need to be rendered. If there is more than one light being passed to the pass, thenthe scissor is defined to be the rectangle which covers all lights in screen-space. Directionallights are ignored since they are infinite.

This option does not need to be specified if you are using a standard additiveshadow mode, i.e. SHADOWTYPE STENCIL ADDITIVE or SHADOW-TYPE TEXTURE ADDITIVE, since it is the default behaviour to use a scissor for eachadditive shadow pass. However, if you’re not using shadows, or you’re using [IntegratedTexture Shadows], page 189 where passes are specified in a custom manner, then thiscould be of use to you.

light clip planes

Sets whether when rendering this pass, triangle setup will be limited to clipping volumecovered by the light. Directional lights are ignored, point lights clip to a cube the size ofthe attenuation range or the light, and spotlights clip to a pyramid bounding the spotlightangle and attenuation range.

Format: light clip planes <on|off>

Default: light clip planes off

This option will only function if there is a single non-directional light being used in thispass. If there is more than one light, or only directional lights, then no clipping will occur.If there are no lights at all then the objects won’t be rendered at all.

When using a standard additive shadow mode, ie SHADOWTYPE STENCIL ADDITIVEor SHADOWTYPE TEXTURE ADDITIVE, you have the option of enabling clipping forall light passes by calling SceneManager::setShadowUseLightClipPlanes regardless of thispass setting, since rendering is done lightwise anyway. This is off by default since usingclip planes is not always faster - it depends on how much of the scene the light volumescover. Generally the smaller your lights are the more chance you’ll see a benefit ratherthan a penalty from clipping. If you’re not using shadows, or you’re using [IntegratedTexture Shadows], page 189 where passes are specified in a custom manner, then specifythe option per-pass using this attribute.

A specific note about OpenGL: user clip planes are completely ignored when you usean ARB vertex program. This means light clip planes won’t help much if you use ARBvertex programs on GL, although OGRE will perform some optimisation of its own, inthat if it sees that the clip volume is completely off-screen, it won’t perform a render atall. When using GLSL, user clipping can be used but you have to use glClipVertex in your


shader, see the GLSL documentation for more information. In Direct3D user clip planesare always respected.

illumination stage

When using an additive lighting mode (SHADOWTYPE STENCIL ADDITIVE or SHAD-OWTYPE TEXTURE ADDITIVE), the scene is rendered in 3 discrete stages, ambient (orpre-lighting), per-light (once per light, with shadowing) and decal (or post-lighting). UsuallyOGRE figures out how to categorise your passes automatically, but there are some effectsyou cannot achieve without manually controlling the illumination. For example speculareffects are muted by the typical sequence because all textures are saved until the ’decal’stage which mutes the specular effect. Instead, you could do texturing within the per-lightstage if it’s possible for your material and thus add the specular on after the decal texturing,and have no post-light rendering.

If you assign an illumination stage to a pass you have to assign it to all passes in thetechnique otherwise it will be ignored. Also note that whilst you can have more than onepass in each group, they cannot alternate, ie all ambient passes will be before all per-lightpasses, which will also be before all decal passes. Within their categories the passes willretain their ordering though.

Format: illumination stage <ambient|per light|decal>

Default: none (autodetect)

normalise normals

Sets whether or not this pass renders with all vertex normals being automatically re-normalised.

Format: normalise normals <on|off>

Scaling objects causes normals to also change magnitude, which can throw off yourlighting calculations. By default, the SceneManager detects this and will automatically re-normalise normals for any scaled object, but this has a cost. If you’d prefer to control thismanually, call SceneManager::setNormaliseNormalsOnScale(false) and then use this optionon materials which are sensitive to normals being resized.

Default: normalise normals off


transparent sorting

Sets if transparent textures should be sorted by depth or not.

Format: transparent sorting <on|off|force>

By default all transparent materials are sorted such that renderables furthest away fromthe camera are rendered first. This is usually the desired behaviour but in certain cases thisdepth sorting may be unnecessary and undesirable. If for example it is necessary to ensurethe rendering order does not change from one frame to the next. In this case you could setthe value to ’off’ to prevent sorting.

You can also use the keyword ’force’ to force transparent sorting on, regardless of othercircumstances. Usually sorting is only used when the pass is also transparent, and has adepth write or read which indicates it cannot reliably render without sorting. By using’force’, you tell OGRE to sort this pass no matter what other circumstances are present.

Default: transparent sorting on

cull hardware

Sets the hardware culling mode for this pass.

Format: cull hardware <clockwise|anticlockwise|none>

A typical way for the hardware rendering engine to cull triangles is based on the ’vertexwinding’ of triangles. Vertex winding refers to the direction in which the vertices arepassed or indexed to in the rendering operation as viewed from the camera, and will witherbe clockwise or anticlockwise (that’s ’counterclockwise’ for you Americans out there ;).If the option ’cull hardware clockwise’ is set, all triangles whose vertices are viewed inclockwise order from the camera will be culled by the hardware. ’anticlockwise’ is thereverse (obviously), and ’none’ turns off hardware culling so all triagles are rendered (usefulfor creating 2-sided passes).

Default: cull hardware clockwiseNB this is the same as OpenGL’s default but the opposite of Direct3D’s default (becauseOgre uses a right-handed coordinate system like OpenGL).


cull software

Sets the software culling mode for this pass.

Format: cull software <back|front|none>

In some situations the engine will also cull geometry in software before sending it to thehardware renderer. This setting only takes effect on SceneManager’s that use it (since it isbest used on large groups of planar world geometry rather than on movable geometry sincethis would be expensive), but if used can cull geometry before it is sent to the hardware.In this case the culling is based on whether the ’back’ or ’front’ of the triangle is facingthe camera - this definition is based on the face normal (a vector which sticks out of thefront side of the polygon perpendicular to the face). Since Ogre expects face normalsto be on anticlockwise side of the face, ’cull software back’ is the software equivalent of’cull hardware clockwise’ setting, which is why they are both the default. The naming isdifferent to reflect the way the culling is done though, since most of the time face normals arepre-calculated and they don’t have to be the way Ogre expects - you could set ’cull hardwarenone’ and completely cull in software based on your own face normals, if you have the rightSceneManager which uses them.

Default: cull software back

lighting

Sets whether or not dynamic lighting is turned on for this pass or not. If lighting is turnedoff, all objects rendered using the pass will be fully lit. This attribute has no effect if avertex program is used.

Format: lighting <on|off>

Turning dynamic lighting off makes any ambient, diffuse, specular, emissive and shadingproperties for this pass redundant. When lighting is turned on, objects are lit according totheir vertex normals for diffuse and specular light, and globally for ambient and emissive.

Default: lighting on


shading

Sets the kind of shading which should be used for representing dynamic lighting for thispass.

Format: shading <flat|gouraud|phong>

When dynamic lighting is turned on, the effect is to generate colour values at each vertex.Whether these values are interpolated across the face (and how) depends on this setting.

flat No interpolation takes place. Each face is shaded with a single colour deter-mined from the first vertex in the face.

gouraud Colour at each vertex is linearly interpolated across the face.

phong Vertex normals are interpolated across the face, and these are used to determinecolour at each pixel. Gives a more natural lighting effect but is more expensiveand works better at high levels of tessellation. Not supported on all hardware.

Default: shading gouraud

polygon mode

Sets how polygons should be rasterised, i.e. whether they should be filled in, or just drawnas lines or points.

Format: polygon mode <solid|wireframe|points>

solid The normal situation - polygons are filled in.

wireframe Polygons are drawn in outline only.

points Only the points of each polygon are rendered.

Default: polygon mode solid

polygon mode overrideable

Sets whether or not the [polygon mode], page 38 set on this pass can be downgraded bythe camera, if the camera itself is set to a lower polygon mode. If set to false, this pass willalways be rendered at its own chosen polygon mode no matter what the camera says. Thedefault is true.


Format: polygon mode overrideable <true|false>

fog override

Tells the pass whether it should override the scene fog settings, and enforce it’s own. Veryuseful for things that you don’t want to be affected by fog when the rest of the scene isfogged, or vice versa. Note that this only affects fixed-function fog - the original scenefog parameters are still sent to shaders which use the fog params parameter binding (thisallows you to turn off fixed function fog and calculate it in the shader instead; if you wantto disable shader fog you can do that through shader parameters anyway).

Format: fog override <override?> [<type> <colour> <density> <start> <end>]

Default: fog override false

If you specify ’true’ for the first parameter and you supply the rest of the parameters,you are telling the pass to use these fog settings in preference to the scene settings, whateverthey might be. If you specify ’true’ but provide no further parameters, you are telling thispass to never use fogging no matter what the scene says. Here is an explanation of theparameters:

type none = No fog, equivalent of just using ’fog override true’linear = Linear fog from the <start> and <end> distancesexp = Fog increases exponentially from the camera (fog = 1/e^(distance *density)), use <density> param to control itexp2 = Fog increases at the square of FOG EXP, i.e. even quicker (fog =1/e^(distance * density)^2), use <density> param to control it

colour Sequence of 3 floating point values from 0 to 1 indicating the red, green andblue intensities

density The density parameter used in the ’exp’ or ’exp2’ fog types. Not used in linearmode but param must still be there as a placeholder

start The start distance from the camera of linear fog. Must still be present in othermodes, even though it is not used.

end The end distance from the camera of linear fog. Must still be present in othermodes, even though it is not used.

Example: fog override true exp 1 1 1 0.002 100 10000


colour write

Sets whether or not this pass renders with colour writing on or not.

Format: colour write <on|off>

If colour writing is off no visible pixels are written to the screen during this pass. Youmight think this is useless, but if you render with colour writing off, and with very minimalother settings, you can use this pass to initialise the depth buffer before subsequently ren-dering other passes which fill in the colour data. This can give you significant performanceboosts on some newer cards, especially when using complex fragment programs, because ifthe depth check fails then the fragment program is never run.

Default: colour write on

start light

Sets the first light which will be considered for use with this pass.

Format: start light <number>

You can use this attribute to offset the starting point of the lights for this pass. In otherwords, if you set start light to 2 then the first light to be processed in that pass will be thethird actual light in the applicable list. You could use this option to use different passes toprocess the first couple of lights versus the second couple of lights for example, or use it inconjunction with the [iteration], page 41 option to start the iteration from a given point inthe list (e.g. doing the first 2 lights in the first pass, and then iterating every 2 lights fromthen on perhaps).

Default: start light 0

max lights

Sets the maximum number of lights which will be considered for use with this pass.

Format: max lights <number>

The maximum number of lights which can be used when rendering fixed-function ma-terials is set by the rendering system, and is typically set at 8. When you are using theprogrammable pipeline (See Section 3.1.9 [Using Vertex/Geometry/Fragment Programs ina Pass], page 79) this limit is dependent on the program you are running, or, if you use


’iteration once per light’ or a variant (See [iteration], page 41), it effectively only boundedby the number of passes you are willing to use. If you are not using pass iteration, the lightlimit applies once for this pass. If you are using pass iteration, the light limit applies acrossall iterations of this pass - for example if you have 12 lights in range with an ’iterationonce per light’ setup but your max lights is set to 4 for that pass, the pass will only iterate4 times.

Default: max lights 8

iteration

Sets whether or not this pass is iterated, i.e. issued more than once.

Format 1: iteration <once | once per light> [lightType]

Format 2: iteration <number> [<per light> [lightType]]

Format 3: iteration <number> [<per n lights> <num lights> [lightType]]

Examples:

iteration onceThe pass is only executed once which is the default behaviour.

iteration once per light pointThe pass is executed once for each point light.

iteration 5 The render state for the pass will be setup and then the draw call will execute5 times.

iteration 5 per light pointThe render state for the pass will be setup and then the draw call will execute5 times. This will be done for each point light.

iteration 1 per n lights 2 pointThe render state for the pass will be setup and the draw call executed once forevery 2 lights.

By default, passes are only issued once. However, if you use the programmable pipeline,or you wish to exceed the normal limits on the number of lights which are supported, youmight want to use the once per light option. In this case, only light index 0 is ever used, andthe pass is issued multiple times, each time with a different light in light index 0. Clearlythis will make the pass more expensive, but it may be the only way to achieve certain effectssuch as per-pixel lighting effects which take into account 1..n lights.


Using a number instead of "once" instructs the pass to iterate more than once after therender state is setup. The render state is not changed after the initial setup so repeateddraw calls are very fast and ideal for passes using programmable shaders that must iteratemore than once with the same render state i.e. shaders that do fur, motion blur, specialfiltering.

If you use once per light, you should also add an ambient pass to the technique beforethis pass, otherwise when no lights are in range of this object it will not get rendered atall; this is important even when you have no ambient light in the scene, because you wouldstill want the objects silhouette to appear.

The lightType parameter to the attribute only applies if you use once per light,per light, or per n lights and restricts the pass to being run for lights of a single type(either ’point’, ’directional’ or ’spot’). In the example, the pass will be run once per pointlight. This can be useful because when you’re writing a vertex / fragment program it isa lot easier if you can assume the kind of lights you’ll be dealing with. However at leastpoint and directional lights can be dealt with in one way.

Default: iteration once

Example: Simple Fur shader material script that uses a second pass with 10 iterationsto grow the fur:// GLSL simple Furvertex_program GLSLDemo/FurVS glsl{source fur.vertdefault_params{

param_named_auto lightPosition light_position_object_space 0param_named_auto eyePosition camera_position_object_spaceparam_named_auto passNumber pass_numberparam_named_auto multiPassNumber pass_iteration_numberparam_named furLength float 0.15

}}

fragment_program GLSLDemo/FurFS glsl{source fur.fragdefault_params{

param_named Ka float 0.2param_named Kd float 0.5


param_named Ks float 0.0param_named furTU int 0

}}

material Fur{technique GLSL{

pass base_coat{ambient 0.7 0.7 0.7diffuse 0.5 0.8 0.5specular 1.0 1.0 1.0 1.5

vertex_program_ref GLSLDemo/FurVS{}

fragment_program_ref GLSLDemo/FurFS{}

texture_unit{texture Fur.tgatex_coord_set 0filtering trilinear

}

}

pass grow_fur{ambient 0.7 0.7 0.7diffuse 0.8 1.0 0.8specular 1.0 1.0 1.0 64depth_write off

scene_blend src_alpha oneiteration 10

vertex_program_ref GLSLDemo/FurVS{}

fragment_program_ref GLSLDemo/FurFS


{}

texture_unit{texture Fur.tgatex_coord_set 0filtering trilinear

}}

}}

Note: use gpu program auto parameters [pass number], page 91 and[pass iteration number], page 92 to tell the vertex, geometry or fragment pro-gram the pass number and iteration number.

point size

This setting allows you to change the size of points when rendering a point list, or a list ofpoint sprites. The interpretation of this command depends on the [point size attenuation],page 45 option - if it is off (the default), the point size is in screen pixels, if it is on, itexpressed as normalised screen coordinates (1.0 is the height of the screen) when the pointis at the origin.

NOTE: Some drivers have an upper limit on the size of points they support - this caneven vary between APIs on the same card! Don’t rely on point sizes that cause the pointsto get very large on screen, since they may get clamped on some cards. Upper sizes canrange from 64 to 256 pixels.

Format: point size <size>

Default: point size 1.0

point sprites

This setting specifies whether or not hardware point sprite rendering is enabled for thispass. Enabling it means that a point list is rendered as a list of quads rather than a list ofdots. It is very useful to use this option if you’re using a BillboardSet and only need to usepoint oriented billboards which are all of the same size. You can also use it for any otherpoint list render.


Format: point sprites <on|off>

Default: point sprites off

point size attenuation

Defines whether point size is attenuated with view space distance, and in what fashion. Thisoption is especially useful when you’re using point sprites (See [point sprites], page 44) sinceit defines how they reduce in size as they get further away from the camera. You can alsodisable this option to make point sprites a constant screen size (like points), or enable it forpoints so they change size with distance.

You only have to provide the final 3 parameters if you turn attenuation on. The formulafor attenuation is that the size of the point is multiplied by 1 / (constant + linear * dist +quadratic * d^2); therefore turning it off is equivalent to (constant = 1, linear = 0, quadratic= 0) and standard perspective attenuation is (constant = 0, linear = 1, quadratic = 0).The latter is assumed if you leave out the final 3 parameters when you specify ’on’.

Note that the resulting attenuated size is clamped to the minimum and maximum pointsize, see the next section.

Format: point size attenuation <on|off> [constant linear quadratic] Default:point size attenuation off

point size min

Sets the minimum point size after attenuation ([point size attenuation], page 45). Fordetails on the size metrics, See [point size], page 44.

Format: point size min <size> Default: point size min 0

point size max

Sets the maximum point size after attenuation ([point size attenuation], page 45). Fordetails on the size metrics, See [point size], page 44. A value of 0 means the maximum isset to the same as the max size reported by the current card.

Format: point size max <size> Default: point size max 0

3.1.3 Texture Units

Here are the attributes you can use in a ’texture unit’ section of a .material script:


Available Texture Layer Attributes

• [texture alias], page 46• [texture], page 47• [anim texture], page 50• [cubic texture], page 50• [tex coord set], page 52• [tex address mode], page 53• [tex border colour], page 53• [filtering], page 54• [max anisotropy], page 55• [mipmap bias], page 55• [colour op], page 55• [colour op ex], page 56• [colour op multipass fallback], page 58• [alpha op ex], page 59• [env map], page 59• [scroll], page 60• [scroll anim], page 60• [rotate], page 60• [rotate anim], page 61• [scale], page 61• [wave xform], page 61• [transform], page 62• [binding type], page 51• [content type], page 51

You can also use a nested ’texture source’ section in order to use a special add-in as asource of texture data, See Chapter 6 [External Texture Sources], page 176 for details.


texture alias

Sets the alias name for this texture unit.

Format: texture alias <name>

Example: texture alias NormalMap


Setting the texture alias name is useful if this material is to be inherited by other othermaterials and only the textures will be changed in the new material.(See Section 3.1.12[Texture Aliases], page 100)

Default: If a texture unit has a name then the texture alias defaults to the texture unitname.

texture

Sets the name of the static texture image this layer will use.

Format: texture <texturename> [<type>] [unlimited | numMipMaps] [alpha] [<PixelFor-mat>] [gamma]

Example: texture funkywall.jpg

This setting is mutually exclusive with the anim texture attribute. Note that the texturefile cannot include spaces. Those of you Windows users who like spaces in filenames, pleaseget over it and use underscores instead.

The ’type’ parameter allows you to specify a the type of texture to create - the default is’2d’, but you can override this; here’s the full list:

1d A 1-dimensional texture; that is, a texture which is only 1 pixel high. Thesekinds of textures can be useful when you need to encode a function in a textureand use it as a simple lookup, perhaps in a fragment program. It is impor-tant that you use this setting when you use a fragment program which uses1-dimensional texture coordinates, since GL requires you to use a texture typethat matches (D3D will let you get away with it, but you ought to plan forcross-compatibility). Your texture widths should still be a power of 2 for bestcompatibility and performance.

2d The default type which is assumed if you omit it, your texture has a width anda height, both of which should preferably be powers of 2, and if you can, makethem square because this will look best on the most hardware. These can beaddressed with 2D texture coordinates.

3d A 3 dimensional texture i.e. volume texture. Your texture has a width, a height,both of which should be powers of 2, and has depth. These can be addressedwith 3d texture coordinates i.e. through a pixel shader.

cubic This texture is made up of 6 2D textures which are pasted around the inside ofa cube. Can be addressed with 3D texture coordinates and are useful for cubicreflection maps and normal maps.

The ’numMipMaps’ option allows you to specify the number of mipmaps to generate forthis texture. The default is ’unlimited’ which means mips down to 1x1 size are generated.


You can specify a fixed number (even 0) if you like instead. Note that if you use the sametexture in many material scripts, the number of mipmaps generated will conform to thenumber specified in the first texture unit used to load the texture - so be consistent withyour usage.

The ’alpha’ option allows you to specify that a single channel (luminance) texture shouldbe loaded as alpha, rather than the default which is to load it into the red channel. Thiscan be helpful if you want to use alpha-only textures in the fixed function pipeline.

Default: none

The <PixelFormat> option allows you to specify the desired pixel format of the textureto create, which may be different to the pixel format of the texture file being loaded. Bearin mind that the final pixel format will be constrained by hardware capabilities so you maynot get exactly what you ask for. The available options are:

PF L8 8-bit pixel format, all bits luminance.

PF L16 16-bit pixel format, all bits luminance.

PF A8 8-bit pixel format, all bits alpha.

PF A4L4 8-bit pixel format, 4 bits alpha, 4 bits luminance.

PF BYTE LA2 byte pixel format, 1 byte luminance, 1 byte alpha

PF R5G6B516-bit pixel format, 5 bits red, 6 bits green, 5 bits blue.

PF B5G6R516-bit pixel format, 5 bits blue, 6 bits green, 5 bits red.

PF R3G3B28-bit pixel format, 3 bits red, 3 bits green, 2 bits blue.

PF A4R4G4B416-bit pixel format, 4 bits for alpha, red, green and blue.

PF A1R5G5B516-bit pixel format, 1 bit for alpha, 5 bits for red, green and blue.

PF R8G8B824-bit pixel format, 8 bits for red, green and blue.

PF B8G8R824-bit pixel format, 8 bits for blue, green and red.

PF A8R8G8B832-bit pixel format, 8 bits for alpha, red, green and blue.

PF A8B8G8R832-bit pixel format, 8 bits for alpha, blue, green and red.


PF B8G8R8A832-bit pixel format, 8 bits for blue, green, red and alpha.

PF R8G8B8A832-bit pixel format, 8 bits for red, green, blue and alpha.

PF X8R8G8B832-bit pixel format, 8 bits for red, 8 bits for green, 8 bits for blue likePF A8R8G8B8, but alpha will get discarded

PF X8B8G8R832-bit pixel format, 8 bits for blue, 8 bits for green, 8 bits for red likePF A8B8G8R8, but alpha will get discarded

PF A2R10G10B1032-bit pixel format, 2 bits for alpha, 10 bits for red, green and blue.

PF A2B10G10R1032-bit pixel format, 2 bits for alpha, 10 bits for blue, green and red.

PF FLOAT16 R16-bit pixel format, 16 bits (float) for red

PF FLOAT16 RGB48-bit pixel format, 16 bits (float) for red, 16 bits (float) for green, 16 bits(float) for blue

PF FLOAT16 RGBA64-bit pixel format, 16 bits (float) for red, 16 bits (float) for green, 16 bits(float) for blue, 16 bits (float) for alpha

PF FLOAT32 R16-bit pixel format, 16 bits (float) for red

PF FLOAT32 RGB96-bit pixel format, 32 bits (float) for red, 32 bits (float) for green, 32 bits(float) for blue

PF FLOAT32 RGBA128-bit pixel format, 32 bits (float) for red, 32 bits (float) for green, 32 bits(float) for blue, 32 bits (float) for alpha

PF SHORT RGBA64-bit pixel format, 16 bits for red, green, blue and alpha

The ’gamma’ option informs the renderer that you want the graphics hardware to per-form gamma correction on the texture values as they are sampled for rendering. This isonly applicable for textures which have 8-bit colour channels (e.g.PF R8G8B8). Often,8-bit per channel textures will be stored in gamma space in order to increase the precisionof the darker colours (http://en.wikipedia.org/wiki/Gamma_correction) but this canthrow out blending and filtering calculations since they assume linear space colour values.For the best quality shading, you may want to enable gamma correction so that the hard-ware converts the texture values to linear space for you automatically when sampling thetexture, then the calculations in the pipeline can be done in a reliable linear colour space.

http://en.wikipedia.org/wiki/Gamma_correction


When rendering to a final 8-bit per channel display, you’ll also want to convert back togamma space which can be done in your shader (by raising to the power 1/2.2) or you canenable gamma correction on the texture being rendered to or the render window. Notethat the ’gamma’ option on textures is applied on loading the texture so must be specifiedconsistently if you use this texture in multiple places.

anim texture

Sets the images to be used in an animated texture layer. In this case an animated texturelayer means one which has multiple frames, each of which is a separate image file. Thereare 2 formats, one for implicitly determined image names, one for explicitly named images.

Format1 (short): anim texture <base name> <num frames> <duration>

Example: anim texture flame.jpg 5 2.5

This sets up an animated texture layer made up of 5 frames named flame 0.jpg,flame 1.jpg, flame 2.jpg etc, with an animation length of 2.5 seconds (2fps). If duration isset to 0, then no automatic transition takes place and frames must be changed manuallyin code.

Format2 (long): anim texture <frame1> <frame2> ... <duration>

Example: anim texture flamestart.jpg flamemore.png flameagain.jpg moreflame.jpg last-flame.tga 2.5

This sets up the same duration animation but from 5 separately named image files. Thefirst format is more concise, but the second is provided if you cannot make your imagesconform to the naming standard required for it.

Default: none

cubic texture

Sets the images used in a cubic texture, i.e. one made up of 6 individual images makingup the faces of a cube. These kinds of textures are used for reflection maps (if hardwaresupports cubic reflection maps) or skyboxes. There are 2 formats, a brief format expectingimage names of a particular format and a more flexible but longer format for arbitrarily


named textures.

Format1 (short): cubic texture <base name> <combinedUVW|separateUV>

The base name in this format is something like ’skybox.jpg’, and the system will expectyou to provide skybox fr.jpg, skybox bk.jpg, skybox up.jpg, skybox dn.jpg, skybox lf.jpg,and skybox rt.jpg for the individual faces.

Format2 (long): cubic texture <front> <back> <left> <right> <up> <down> separateUV

In this case each face is specified explicitly, incase you don’t want to conform to theimage naming standards above. You can only use this for the separateUV version since thecombinedUVW version requires a single texture name to be assigned to the combined 3Dtexture (see below).

In both cases the final parameter means the following:

combinedUVWThe 6 textures are combined into a single ’cubic’ texture map which is then ad-dressed using 3D texture coordinates with U, V and W components. Necessaryfor reflection maps since you never know which face of the box you are goingto need. Note that not all cards support cubic environment mapping.

separateUVThe 6 textures are kept separate but are all referenced by this single texturelayer. One texture at a time is active (they are actually stored as 6 frames),and they are addressed using standard 2D UV coordinates. This type is goodfor skyboxes since only one face is rendered at one time and this has moreguaranteed hardware support on older cards.

Default: none

binding type

Tells this texture unit to bind to either the fragment processing unit or the vertex processingunit (for Section 3.1.10 [Vertex Texture Fetch], page 95).

Format: binding type <vertex|fragment> Default: binding type fragment

content type

Tells this texture unit where it should get its content from. The default is to get tex-ture content from a named texture, as defined with the [texture], page 47, [cubic texture],


page 50, [anim texture], page 50 attributes. However you can also pull texture informationfrom other automated sources. The options are:

named The default option, this derives texture content from a texture name, loadedby ordinary means from a file or having been manually created with a givenname.

shadow This option allows you to pull in a shadow texture, and is only valid whenyou use texture shadows and one of the ’custom sequence’ shadowing types(See Chapter 7 [Shadows], page 180). The shadow texture in question will befrom the ’n’th closest light that casts shadows, unless you use light-based passiteration or the light start option which may start the light index higher. Whenyou use this option in multiple texture units within the same pass, each onereferences the next shadow texture. The shadow texture index is reset in thenext pass, in case you want to take into account the same shadow textures againin another pass (e.g. a separate specular / gloss pass). By using this option,the correct light frustum projection is set up for you for use in fixed-function,if you use shaders just reference the texture viewproj matrix auto parameterin your shader.

compositorThis option allows you to reference a texture from a compositor, and is onlyvalid when the pass is rendered within a compositor sequence. This can be ei-ther in a render scene directive inside a compositor script, or in a general passin a viewport that has a compositor attached. Note that this is a reference only,meaning that it does not change the render order. You must make sure thatthe order is reasonable for what you are trying to achieve (for example, texturepooling might cause the referenced texture to be overwritten by something elseby the time it is referenced).

The extra parameters for the content type are only required for this type:

The first is the name of the compositor being referenced. (Required)

The second is the name of the texture to reference in the compositor. (Re-quired)

The third is the index of the texture to take, in case of an MRT. (Optional)

Format: content type <named|shadow|compositor> [<Referenced Compositor Name>][<Referenced Texture Name>] [<Referenced MRT Index>]

Default: content type named

Example: content type compositor DepthCompositor OutputTexture


tex coord set

Sets which texture coordinate set is to be used for this texture layer. A mesh can definemultiple sets of texture coordinates, this sets which one this material uses.

Format: tex coord set <set num>

Example: tex coord set 2

Default: tex coord set 0

tex address mode

Defines what happens when texture coordinates exceed 1.0 for this texture layer.You canuse the simple format to specify the addressing mode for all 3 potential texture coordinatesat once, or you can use the 2/3 parameter extended format to specify a different mode pertexture coordinate.

Simple Format: tex address mode <uvw mode>Extended Format: tex address mode <u mode> <v mode> [<w mode>]

wrap Any value beyond 1.0 wraps back to 0.0. Texture is repeated.

clamp Values beyond 1.0 are clamped to 1.0. Texture ’streaks’ beyond 1.0 since lastline of pixels is used across the rest of the address space. Useful for textureswhich need exact coverage from 0.0 to 1.0 without the ’fuzzy edge’ wrap giveswhen combined with filtering.

mirror Texture flips every boundary, meaning texture is mirrored every 1.0 u or v

border Values outside the range [0.0, 1.0] are set to the border colour, you might alsoset the [tex border colour], page 53 attribute too.

Default: tex address mode wrap

tex border colour

Sets the border colour of border texture address mode (see [tex address mode], page 53).

Format: tex border colour <red> <green> <blue> [<alpha>]NB valid colour values are between 0.0 and 1.0.


Example: tex border colour 0.0 1.0 0.3

Default: tex border colour 0.0 0.0 0.0 1.0

filtering

Sets the type of texture filtering used when magnifying or minifying a texture. There are2 formats to this attribute, the simple format where you simply specify the name of apredefined set of filtering options, and the complex format, where you individually set theminification, magnification, and mip filters yourself.

Simple FormatFormat: filtering <none|bilinear|trilinear|anisotropic>Default: filtering bilinear

With this format, you only need to provide a single parameter which is one of the following:

none No filtering or mipmapping is used. This is equivalent to the complex format’filtering point point none’.

bilinear 2x2 box filtering is performed when magnifying or reducing a texture, and amipmap is picked from the list but no filtering is done between the levels ofthe mipmaps. This is equivalent to the complex format ’filtering linear linearpoint’.

trilinear 2x2 box filtering is performed when magnifying and reducing a texture, andthe closest 2 mipmaps are filtered together. This is equivalent to the complexformat ’filtering linear linear linear’.

anisotropicThis is the same as ’trilinear’, except the filtering algorithm takes account ofthe slope of the triangle in relation to the camera rather than simply doinga 2x2 pixel filter in all cases. This makes triangles at acute angles look lessfuzzy. Equivalent to the complex format ’filtering anisotropic anisotropic lin-ear’. Note that in order for this to make any difference, you must also set the[max anisotropy], page 55 attribute too.

Complex FormatFormat: filtering <minification> <magnification> <mip>Default: filtering linear linear point

This format gives you complete control over the minification, magnification, and mip filters.Each parameter can be one of the following:


none Nothing - only a valid option for the ’mip’ filter , since this turns mipmappingoff completely. The lowest setting for min and mag is ’point’.

point Pick the closet pixel in min or mag modes. In mip mode, this picks the closetmatching mipmap.

linear Filter a 2x2 box of pixels around the closest one. In the ’mip’ filter this enablesfiltering between mipmap levels.

anisotropicOnly valid for min and mag modes, makes the filter compensate for camera-space slope of the triangles. Note that in order for this to make any difference,you must also set the [max anisotropy], page 55 attribute too.

max anisotropy

Sets the maximum degree of anisotropy that the renderer will try to compensate for whenfiltering textures. The degree of anisotropy is the ratio between the height of the texturesegment visible in a screen space region versus the width - so for example a floor plane,which stretches on into the distance and thus the vertical texture coordinates change muchfaster than the horizontal ones, has a higher anisotropy than a wall which is facing you headon (which has an anisotropy of 1 if your line of sight is perfectly perpendicular to it). Youshould set the max anisotropy value to something greater than 1 to begin compensating;higher values can compensate for more acute angles. The maximum value is determined bythe hardware, but it is usually 8 or 16.

In order for this to be used, you have to set the minification and/or the magnification[filtering], page 54 option on this texture to anisotropic.

Format: max anisotropy <value>Default: max anisotropy 1

mipmap bias

Sets the bias value applied to the mipmapping calculation, thus allowing you to alter thedecision of which level of detail of the texture to use at any distance. The bias value isapplied after the regular distance calculation, and adjusts the mipmap level by 1 level foreach unit of bias. Negative bias values force larger mip levels to be used, positive bias valuesforce smaller mip levels to be used. The bias is a floating point value so you can use valuesin between whole numbers for fine tuning.

In order for this option to be used, your hardware has to support mipmap biasing (exposedthrough the render system capabilities), and your minification [filtering], page 54 has to beset to point or linear.

Format: mipmap bias <value>Default: mipmap bias 0

colour op

Determines how the colour of this texture layer is combined with the one below it (or thelighting effect on the geometry if this is the first layer).


Format: colour op <replace|add|modulate|alpha blend>

This method is the simplest way to blend texture layers, because it requires only oneparameter, gives you the most common blending types, and automatically sets up 2 blendingmethods: one for if single-pass multitexturing hardware is available, and another for ifit is not and the blending must be achieved through multiple rendering passes. It is,however, quite limited and does not expose the more flexible multitexturing operations,simply because these can’t be automatically supported in multipass fallback mode. If wantto use the fancier options, use [colour op ex], page 56, but you’ll either have to be sure thatenough multitexturing units will be available, or you should explicitly set a fallback using[colour op multipass fallback], page 58.

replace Replace all colour with texture with no adjustment.

add Add colour components together.

modulate Multiply colour components together.

alpha blendBlend based on texture alpha.

Default: colour op modulate

colour op ex

This is an extended version of the [colour op], page 55 attribute which allows extremelydetailed control over the blending applied between this and earlier layers. Multitexturinghardware can apply more complex blending operations that multipass blending, but youare limited to the number of texture units which are available in hardware.

Format: colour op ex <operation> <source1> <source2> [<manual factor>] [<man-ual colour1>] [<manual colour2>]

Example colour op ex add signed src manual src current 0.5

See the IMPORTANT note below about the issues between multipass and multitexturingthat using this method can create. Texture colour operations determine how the final colourof the surface appears when rendered. Texture units are used to combine colour values fromvarious sources (e.g. the diffuse colour of the surface from lighting calculations, combinedwith the colour of the texture). This method allows you to specify the ’operation’ to beused, i.e. the calculation such as adds or multiplies, and which values to use as arguments,


such as a fixed value or a value from a previous calculation.

Operation optionssource1 Use source1 without modification

source2 Use source2 without modification

modulate Multiply source1 and source2 together.

modulate x2Multiply source1 and source2 together, then by 2 (brightening).

modulate x4Multiply source1 and source2 together, then by 4 (brightening).

add Add source1 and source2 together.

add signedAdd source1 and source2 then subtract 0.5.

add smoothAdd source1 and source2, subtract the product

subtract Subtract source2 from source1

blend diffuse alphaUse interpolated alpha value from vertices to scale source1, thenadd source2 scaled by (1-alpha).

blend texture alphaAs blend diffuse alpha but use alpha from texture

blend current alphaAs blend diffuse alpha but use current alpha from previous stages(same as blend diffuse alpha for first layer)

blend manualAs blend diffuse alpha but use a constant manual alpha value spec-ified in <manual>

dotproductThe dot product of source1 and source2

blend diffuse colourUse interpolated colour value from vertices to scale source1, thenadd source2 scaled by (1-colour).

Source1 and source2 optionssrc current

The colour as built up from previous stages.

src textureThe colour derived from the texture assigned to this layer.


src diffuse The interpolated diffuse colour from the vertices (same as’src current’ for first layer).

src specularThe interpolated specular colour from the vertices.

src manualThe manual colour specified at the end of the command.

For example ’modulate’ takes the colour results of the previous layer, and multiplies themwith the new texture being applied. Bear in mind that colours are RGB values from 0.0-1.0so multiplying them together will result in values in the same range, ’tinted’ by the multiply.Note however that a straight multiply normally has the effect of darkening the textures -for this reason there are brightening operations like modulate x2. Note that because of thelimitations on some underlying APIs (Direct3D included) the ’texture’ argument can onlybe used as the first argument, not the second.

Note that the last parameter is only required if you decide to pass a value manually intothe operation. Hence you only need to fill these in if you use the ’blend manual’ operation.

IMPORTANT: Ogre tries to use multitexturing hardware to blend texture layers to-gether. However, if it runs out of texturing units (e.g. 2 of a GeForce2, 4 on a GeForce3) ithas to fall back on multipass rendering, i.e. rendering the same object multiple times withdifferent textures. This is both less efficient and there is a smaller range of blending oper-ations which can be performed. For this reason, if you use this method you really shouldset the colour op multipass fallback attribute to specify which effect you want to fall backon if sufficient hardware is not available (the default is just ’modulate’ which is unlikely tobe what you want if you’re doing swanky blending here). If you wish to avoid having to dothis, use the simpler colour op attribute which allows less flexible blending options but setsup the multipass fallback automatically, since it only allows operations which have directmultipass equivalents.

Default: none (colour op modulate)

colour op multipass fallback

Sets the multipass fallback operation for this layer, if you used colour op ex and not enoughmultitexturing hardware is available.

Format: colour op multipass fallback <src factor> <dest factor>


Example: colour op multipass fallback one one minus dest alpha

Because some of the effects you can create using colour op ex are only supported undermultitexturing hardware, if the hardware is lacking the system must fallback on multipassrendering, which unfortunately doesn’t support as many effects. This attribute is for youto specify the fallback operation which most suits you.

The parameters are the same as in the scene blend attribute; this is because multipassrendering IS effectively scene blending, since each layer is rendered on top of the last usingthe same mechanism as making an object transparent, it’s just being rendered in the sameplace repeatedly to get the multitexture effect. If you use the simpler (and less flexible)colour op attribute you don’t need to call this as the system sets up the fallback for you.

alpha op ex

Behaves in exactly the same away as [colour op ex], page 56 except that it determineshow alpha values are combined between texture layers rather than colour values.The onlydifference is that the 2 manual colours at the end of colour op ex are just single floating-point values in alpha op ex.

env map

Turns on/off texture coordinate effect that makes this layer an environment map.

Format: env map <off|spherical|planar|cubic reflection|cubic normal>

Environment maps make an object look reflective by using automatic texture coordinategeneration depending on the relationship between the objects vertices or normals and theeye.

spherical A spherical environment map. Requires a single texture which is either a fish-eye lens view of the reflected scene, or some other texture which looks good as aspherical map (a texture of glossy highlights is popular especially in car sims).This effect is based on the relationship between the eye direction and the vertexnormals of the object, so works best when there are a lot of gradually changingnormals, i.e. curved objects.

planar Similar to the spherical environment map, but the effect is based on the po-sition of the vertices in the viewport rather than vertex normals. This effectis therefore useful for planar geometry (where a spherical env map would notlook good because the normals are all the same) or objects without normals.


cubic reflectionA more advanced form of reflection mapping which uses a group of 6 texturesmaking up the inside of a cube, each of which is a view if the scene down eachaxis. Works extremely well in all cases but has a higher technical requirementfrom the card than spherical mapping. Requires that you bind a [cubic texture],page 50 to this texture unit and use the ’combinedUVW’ option.

cubic normalGenerates 3D texture coordinates containing the camera space normal vectorfrom the normal information held in the vertex data. Again, full use of thisfeature requires a [cubic texture], page 50 with the ’combinedUVW’ option.

Default: env map off

scroll

Sets a fixed scroll offset for the texture.

Format: scroll <x> <y>

This method offsets the texture in this layer by a fixed amount. Useful for small ad-justments without altering texture coordinates in models. However if you wish to have ananimated scroll effect, see the [scroll anim], page 60 attribute.

scroll anim

Sets up an animated scroll for the texture layer. Useful for creating fixed-speed scrollingeffects on a texture layer (for varying scroll speeds, see [wave xform], page 61).

Format: scroll anim <xspeed> <yspeed>

rotate

Rotates a texture to a fixed angle. This attribute changes the rotational orientation of atexture to a fixed angle, useful for fixed adjustments. If you wish to animate the rotation,see [rotate anim], page 61.

Format: rotate <angle>


The parameter is a anti-clockwise angle in degrees.

rotate anim

Sets up an animated rotation effect of this layer. Useful for creating fixed-speed rotationanimations (for varying speeds, see [wave xform], page 61).

Format: rotate anim <revs per second>

The parameter is a number of anti-clockwise revolutions per second.

scale

Adjusts the scaling factor applied to this texture layer. Useful for adjusting the size oftextures without making changes to geometry. This is a fixed scaling factor, if you wish toanimate this see [wave xform], page 61.

Format: scale <x scale> <y scale>

Valid scale values are greater than 0, with a scale factor of 2 making the texture twiceas big in that dimension etc.

wave xform

Sets up a transformation animation based on a wave function. Useful for more advancedtexture layer transform effects. You can add multiple instances of this attribute to a singletexture layer if you wish.

Format: wave xform <xform type> <wave type> <base> <frequency> <phase> <ampli-tude>

Example: wave xform scale x sine 1.0 0.2 0.0 5.0

xform typescroll x Animate the x scroll value


scroll y Animate the y scroll value

rotate Animate the rotate value

scale x Animate the x scale value

scale y Animate the y scale value

wave type

sine A typical sine wave which smoothly loops between min and maxvalues

triangle An angled wave which increases & decreases at constant speed,changing instantly at the extremes

square Max for half the wavelength, min for the rest with instant transitionbetween

sawtooth Gradual steady increase from min to max over the period with aninstant return to min at the end.

inverse sawtoothGradual steady decrease from max to min over the period, with aninstant return to max at the end.

base The base value, the minimum if amplitude > 0, the maximum if amplitude < 0

frequency The number of wave iterations per second, i.e. speed

phase Offset of the wave start

amplitude The size of the wave

The range of the output of the wave will be base, base+amplitude. So the example abovescales the texture in the x direction between 1 (normal size) and 5 along a sine wave at onecycle every 5 second (0.2 waves per second).

transform

This attribute allows you to specify a static 4x4 transformation matrix for the texture unit,thus replacing the individual scroll, rotate and scale attributes mentioned above.

Format: transform m00 m01 m02 m03 m10 m11 m12 m13 m20 m21 m22 m23 m30 m31m32 m33

The indexes of the 4x4 matrix value above are expressed as m<row><col>.


3.1.4 Declaring Vertex/Geometry/Fragment Programs

In order to use a vertex, geometry or fragment program in your materials (See Section 3.1.9[Using Vertex/Geometry/Fragment Programs in a Pass], page 79), you first have to definethem. A single program definition can be used by any number of materials, the onlyprerequisite is that a program must be defined before being referenced in the pass sectionof a material.

The definition of a program can either be embedded in the .material script itself (inwhich case it must precede any references to it in the script), or if you wish to use the sameprogram across multiple .material files, you can define it in an external .program script.You define the program in exactly the same way whether you use a .program script or a.material script, the only difference is that all .program scripts are guaranteed to have beenparsed before all .material scripts, so you can guarantee that your program has been definedbefore any .material script that might use it. Just like .material scripts, .program scriptswill be read from any location which is on your resource path, and you can define manyprograms in a single script.

Vertex, geometry and fragment programs can be low-level (i.e. assembler code writtento the specification of a given low level syntax such as vs 1 1 or arbfp1) or high-level suchas DirectX9 HLSL, Open GL Shader Language, or nVidia’s Cg language (See [High-levelPrograms], page 67). High level languages give you a number of advantages, such as beingable to write more intuitive code, and possibly being able to target multiple architectures ina single program (for example, the same Cg program might be able to be used in both D3Dand GL, whilst the equivalent low-level programs would require separate techniques, eachtargeting a different API). High-level programs also allow you to use named parametersinstead of simply indexed ones, although parameters are not defined here, they are used inthe Pass.

Here is an example of a definition of a low-level vertex program:

vertex_program myVertexProgram asm{

source myVertexProgram.asmsyntax vs_1_1

}

As you can see, that’s very simple, and defining a fragment or geometry program isexactly the same, just with vertex program replaced with fragment program or geome-try program, respectively. You give the program a name in the header, followed by theword ’asm’ to indicate that this is a low-level program. Inside the braces, you specify wherethe source is going to come from (and this is loaded from any of the resource locations aswith other media), and also indicate the syntax being used. You might wonder why thesyntax specification is required when many of the assembler syntaxes have a header iden-tifying them anyway - well the reason is that the engine needs to know what syntax the


program is in before reading it, because during compilation of the material, we want to skipprograms which use an unsupportable syntax quickly, without loading the program first.

The current supported syntaxes are:

vs 1 1 This is one of the DirectX vertex shader assembler syntaxes.Supported on cards from: ATI Radeon 8500, nVidia GeForce 3

vs 2 0 Another one of the DirectX vertex shader assembler syntaxes.Supported on cards from: ATI Radeon 9600, nVidia GeForce FX 5 series

vs 2 x Another one of the DirectX vertex shader assembler syntaxes.Supported on cards from: ATI Radeon X series, nVidia GeForce FX 6 series

vs 3 0 Another one of the DirectX vertex shader assembler syntaxes.Supported on cards from: ATI Radeon HD 2000+, nVidia GeForce FX 6 series

arbvp1 This is the OpenGL standard assembler format for vertex programs. It’sroughly equivalent to DirectX vs 1 1.

vp20 This is an nVidia-specific OpenGL vertex shader syntax which is a superset ofvs 1.1. ATI Radeon HD 2000+ also supports it.

vp30 Another nVidia-specific OpenGL vertex shader syntax. It is a superset of vs2.0, which is supported on nVidia GeForce FX 5 series and higher. ATI RadeonHD 2000+ also supports it.

vp40 Another nVidia-specific OpenGL vertex shader syntax. It is a superset of vs3.0, which is supported on nVidia GeForce FX 6 series and higher.

ps 1 1, ps 1 2, ps 1 3DirectX pixel shader (ie fragment program) assembler syntax.Supported on cards from: ATI Radeon 8500, nVidia GeForce 3NOTE: for ATI 8500, 9000, 9100, 9200 hardware, this profile can also be usedin OpenGL. The ATI 8500 to 9200 do not support arbfp1 but do support atifsextension in OpenGL which is very similar in function to ps 1 4 in DirectX.Ogre has a built in ps 1 x to atifs compiler that is automatically invoked whenps 1 x is used in OpenGL on ATI hardware.

ps 1 4 DirectX pixel shader (ie fragment program) assembler syntax.Supported on cards from: ATI Radeon 8500, nVidia GeForce FX 5 seriesNOTE: for ATI 8500, 9000, 9100, 9200 hardware, this profile can also be usedin OpenGL. The ATI 8500 to 9200 do not support arbfp1 but do support atifsextension in OpenGL which is very similar in function to ps 1 4 in DirectX.Ogre has a built in ps 1 x to atifs compiler that is automatically invoked whenps 1 x is used in OpenGL on ATI hardware.

ps 2 0 DirectX pixel shader (ie fragment program) assembler syntax.Supported cards: ATI Radeon 9600, nVidia GeForce FX 5 series


ps 2 x DirectX pixel shader (ie fragment program) assembler syntax. This is basicallyps 2 0 with a higher number of instructions.Supported cards: ATI Radeon X series, nVidia GeForce FX 6 series

ps 3 0 DirectX pixel shader (ie fragment program) assembler syntax.Supported cards: ATI Radeon HD 2000+, nVidia GeForce FX6 series

ps 3 x DirectX pixel shader (ie fragment program) assembler syntax.Supported cards: nVidia GeForce FX7 series

arbfp1 This is the OpenGL standard assembler format for fragment programs. It’sroughly equivalent to ps 2 0, which means that not all cards that support basicpixel shaders under DirectX support arbfp1 (for example neither the GeForce3or GeForce4 support arbfp1, but they do support ps 1 1).

fp20 This is an nVidia-specific OpenGL fragment syntax which is a supersetof ps 1.3. It allows you to use the ’nvparse’ format for basic fragmentprograms. It actually uses NV texture shader and NV register combinersto provide functionality equivalent to DirectX’s ps 1 1 under GL, but onlyfor nVidia cards. However, since ATI cards adopted arbfp1 a little earlierthan nVidia, it is mainly nVidia cards like the GeForce3 and GeForce4 thatthis will be useful for. You can find more information about nvparse athttp://developer.nvidia.com/object/nvparse.html.

fp30 Another nVidia-specific OpenGL fragment shader syntax. It is a superset of ps2.0, which is supported on nVidia GeForce FX 5 series and higher. ATI RadeonHD 2000+ also supports it.

fp40 Another nVidia-specific OpenGL fragment shader syntax. It is a superset of ps3.0, which is supported on nVidia GeForce FX 6 series and higher.

gpu gp, gp4 gpAn nVidia-specific OpenGL geometry shader syntax.Supported cards: nVidia GeForce FX8 series

You can get a definitive list of the syntaxes supported by the current card by callingGpuProgramManager::getSingleton().getSupportedSyntax().

Specifying Named Constants for Assembler Shaders

Assembler shaders don’t have named constants (also called uniform parameters) becausethe language does not support them - however if you for example decided to precompileyour shaders from a high-level language down to assembler for performance or obscurity, youmight still want to use the named parameters. Well, you actually can - GpuNamedConstantswhich contains the named parameter mappings has a ’save’ method which you can use towrite this data to disk, where you can reference it later using the manual named constantsdirective inside your assembler program declaration, e.g.


vertex_program myVertexProgram asm{

source myVertexProgram.asmsyntax vs_1_1

manual_named_constants myVertexProgram.constants}

In this case myVertexProgram.constants has been created by callinghighLevelGpuProgram->getNamedConstants().save("myVertexProgram.constants");sometime earlier as preparation, from the original high-level program. Once you’ve usedthis directive, you can use named parameters here even though the assembler programitself has no knowledge of them.

Default Program Parameters

While defining a vertex, geometry or fragment program, you can also specify the defaultparameters to be used for materials which use it, unless they specifically override them.You do this by including a nested ’default params’ section, like so:vertex_program Ogre/CelShadingVP cg{

source Example_CelShading.cgentry_point main_vpprofiles vs_1_1 arbvp1

default_params{

param_named_auto lightPosition light_position_object_space 0param_named_auto eyePosition camera_position_object_spaceparam_named_auto worldViewProj worldviewproj_matrixparam_named shininess float 10

}}

The syntax of the parameter definition is exactly the same as when you define parameterswhen using programs, See [Program Parameter Specification], page 80. Defining defaultparameters allows you to avoid rebinding common parameters repeatedly (clearly in theabove example, all but ’shininess’ are unlikely to change between uses of the program)which makes your material declarations shorter.

Declaring Shared Parameters

Often, not every parameter you want to pass to a shader is unique to that program, andperhaps you want to give the same value to a number of different programs, and a numberof different materials using that program. Shared parameter sets allow you to define a’holding area’ for shared parameters that can then be referenced when you need them inparticular shaders, while keeping the definition of that value in one place. To define a setof shared parameters, you do this:shared_params YourSharedParamsName{

shared_param_named mySharedParam1 float4 0.1 0.2 0.3 0.4


...}

As you can see, you need to use the keyword ’shared params’ and follow it with thename that you will use to identify these shared parameters. Inside the curly braces, youcan define one parameter per line, in a way which is very similar to the [param named],page 92 syntax. The definition of these lines is:

Format: shared param name <param name> <param type> [<[array size]>] [<ini-tial values>]

The param name must be unique within the set, and the param type can be any one offloat, float2, float3, float4, int, int2, int3, int4, matrix2x2, matrix2x3, matrix2x4, matrix3x2,matrix3x3, matrix3x4, matrix4x2, matrix4x3 and matrix4x4. The array size option allowsyou to define arrays of param type should you wish, and if present must be a numberenclosed in square brackets (and note, must be separated from the param type with white-space). If you wish, you can also initialise the parameters by providing a list of values.

Once you have defined the shared parameters, you can reference them insidedefault params and params blocks using [shared params ref], page 93. You can alsoobtain a reference to them in your code via GpuProgramManager::getSharedParameters,and update the values for all instances using them.

High-level Programs

Support for high level vertex and fragment programs is provided through plugins; this is tomake sure that an application using OGRE can use as little or as much of the high-levelprogram functionality as they like. OGRE currently supports 3 high-level program types,Cg (Section 3.1.5 [Cg], page 69) (an API- and card-independent, high-level language whichlets you write programs for both OpenGL and DirectX for lots of cards), DirectX 9 High-Level Shader Language (Section 3.1.6 [HLSL], page 70), and OpenGL Shader Language(Section 3.1.7 [GLSL], page 71). HLSL can only be used with the DirectX rendersystem,and GLSL can only be used with the GL rendersystem. Cg can be used with both, althoughexperience has shown that more advanced programs, particularly fragment programs whichperform a lot of texture fetches, can produce better code in the rendersystem-specific shaderlanguage.

One way to support both HLSL and GLSL is to include separate techniques in thematerial script, each one referencing separate programs. However, if the programs arebasically the same, with the same parameters, and the techniques are complex this can bloatyour material scripts with duplication fairly quickly. Instead, if the only difference is thelanguage of the vertex & fragment program you can use OGRE’s Section 3.1.8 [Unified High-level Programs], page 76 to automatically pick a program suitable for your rendersystemwhilst using a single technique.


Skeletal Animation in Vertex Programs

You can implement skeletal animation in hardware by writing a vertex program whichuses the per-vertex blending indices and blending weights, together with an array of worldmatrices (which will be provided for you by Ogre if you bind the automatic parameter’world matrix array 3x4’). However, you need to communicate this support to Ogre so itdoes not perform skeletal animation in software for you. You do this by adding the followingattribute to your vertex program definition:

includes_skeletal_animation true

When you do this, any skeletally animated entity which uses this material will forgo theusual animation blend and will expect the vertex program to do it, for both vertex positionsand normals. Note that ALL submeshes must be assigned a material which implementsthis, and that if you combine skeletal animation with vertex animation (See Chapter 8[Animation], page 197) then all techniques must be hardware accelerated for any to be.

Morph Animation in Vertex Programs

You can implement morph animation in hardware by writing a vertex program which lin-early blends between the first and second position keyframes passed as positions and thefirst free texture coordinate set, and by binding the animation parametric value to a pa-rameter (which tells you how far to interpolate between the two). However, you need tocommunicate this support to Ogre so it does not perform morph animation in software foryou. You do this by adding the following attribute to your vertex program definition:

includes_morph_animation true

When you do this, any skeletally animated entity which uses this material will forgo theusual software morph and will expect the vertex program to do it. Note that if your modelincludes both skeletal animation and morph animation, they must both be implemented inthe vertex program if either is to be hardware acceleration. Note that ALL submeshes mustbe assigned a material which implements this, and that if you combine skeletal animationwith vertex animation (See Chapter 8 [Animation], page 197) then all techniques must behardware accelerated for any to be.

Pose Animation in Vertex Programs

You can implement pose animation (blending between multiple poses based on weight) ina vertex program by pulling in the original vertex data (bound to position), and as manypose offset buffers as you’ve defined in your ’includes pose animation’ declaration, whichwill be in the first free texture unit upwards. You must also use the animation parametricparameter to define the starting point of the constants which will contain the pose weights;they will start at the parameter you define and fill ’n’ constants, where ’n’ is the maxnumber of poses this shader can blend, i.e. the parameter to includes pose animation.

includes_pose_animation 4

Note that ALL submeshes must be assigned a material which implements this, andthat if you combine skeletal animation with vertex animation (See Chapter 8 [Animation],page 197) then all techniques must be hardware accelerated for any to be.


Vertex texture fetching in vertex programs

If your vertex program makes use of Section 3.1.10 [Vertex Texture Fetch], page 95, youshould declare that with the ’uses vertex texture fetch’ directive. This is enough to tellOgre that your program uses this feature and that hardware support for it should be checked.

uses_vertex_texture_fetch true

Adjacency information in Geometry Programs

Some geometry programs require adjacency information from the geometry. It means thata geometry shader doesn’t only get the information of the primitive it operates on, it alsohas access to its neighbors (in the case of lines or triangles). This directive will tell Ogre tosend the information to the geometry shader.

uses_adjacency_information true

Vertex Programs With Shadows

When using shadows (See Chapter 7 [Shadows], page 180), the use of vertex programs canadd some additional complexities, because Ogre can only automatically deal with everythingwhen using the fixed-function pipeline. If you use vertex programs, and you are also usingshadows, you may need to make some adjustments.

If you use stencil shadows, then any vertex programs which do vertex deformation canbe a problem, because stencil shadows are calculated on the CPU, which does not haveaccess to the modified vertices. If the vertex program is doing standard skeletal animation,this is ok (see section above) because Ogre knows how to replicate the effect in software,but any other vertex deformation cannot be replicated, and you will either have to acceptthat the shadow will not reflect this deformation, or you should turn off shadows for thatobject.

If you use texture shadows, then vertex deformation is acceptable; however, when ren-dering the object into a shadow texture (the shadow caster pass), the shadow has to berendered in a solid colour (linked to the ambient colour for modulative shadows, black foradditive shadows). You must therefore provide an alternative vertex program, so Ogre pro-vides you with a way of specifying one to use when rendering the caster, See [Shadows andVertex Programs], page 93.

3.1.5 Cg programs

In order to define Cg programs, you have to have to load Plugin CgProgramManager.so/.dllat startup, either through plugins.cfg or through your own plugin loading code. They arevery easy to define:fragment_program myCgFragmentProgram cg{

source myCgFragmentProgram.cgentry_point mainprofiles ps_2_0 arbfp1


}

There are a few differences between this and the assembler program - to begin with, wedeclare that the fragment program is of type ’cg’ rather than ’asm’, which indicates thatit’s a high-level program using Cg. The ’source’ parameter is the same, except this timeit’s referencing a Cg source file instead of a file of assembler.

Here is where things start to change. Firstly, we need to define an ’entry point’, which isthe name of a function in the Cg program which will be the first one called as part of thefragment program. Unlike assembler programs, which just run top-to-bottom, Cg programscan include multiple functions and as such you must specify the one which start the ballrolling.

Next, instead of a fixed ’syntax’ parameter, you specify one or more ’profiles’; profiles arehow Cg compiles a program down to the low-level assembler. The profiles have the samenames as the assembler syntax codes mentioned above; the main difference is that youcan list more than one, thus allowing the program to be compiled down to more low-levelsyntaxes so you can write a single high-level program which runs on both D3D and GL. Youare advised to just enter the simplest profiles under which your programs can be compiledin order to give it the maximum compatibility. The ordering also matters; if a card supportsmore than one syntax then the one listed first will be used.

Lastly, there is a final option called ’compile arguments’, where you can specify argu-ments exactly as you would to the cgc command-line compiler, should you wish to.

3.1.6 DirectX9 HLSL

DirectX9 HLSL has a very similar language syntax to Cg but is tied to the DirectX API.The only benefit over Cg is that it only requires the DirectX 9 render system plugin, notany additional plugins. Declaring a DirectX9 HLSL program is very similar to Cg. Here’san example:vertex_program myHLSLVertexProgram hlsl{

source myHLSLVertexProgram.txtentry_point maintarget vs_2_0

}

As you can see, the main syntax is almost identical, except that instead of ’profiles’ witha list of assembler formats, you have a ’target’ parameter which allows a single assemblertarget to be specified - obviously this has to be a DirectX assembler format syntax code.

Important Matrix Ordering Note: One thing to bear in mind is that HLSL allows youto use 2 different ways to multiply a vector by a matrix - mul(v,m) or mul(m,v). Theonly difference between them is that the matrix is effectively transposed. You should usemul(m,v) with the matrices passed in from Ogre - this agrees with the shaders producedfrom tools like RenderMonkey, and is consistent with Cg too, but disagrees with the Dx9


SDK and FX Composer which use mul(v,m) - you will have to switch the parameters tomul() in those shaders.

Note that if you use the float3x4 / matrix3x4 type in your shader, bound to an OGREauto-definition (such as bone matrices) you should use the column major matrices = falseoption (discussed below) in your program definition. This is because OGRE passes float3x4as row-major to save constant space (3 float4’s rather than 4 float4’s with only the top 3values used) and this tells OGRE to pass all matrices like this, so that you can use mul(m,v)consistently for all calculations. OGRE will also to tell the shader to compile in row-majorform (you don’t have to set the /Zpr compile option or #pragma pack(row-major) option,OGRE does this for you). Note that passing bones in float4x3 form is not supported byOGRE, but you don’t need it given the above.

Advanced options

preprocessor defines <defines>This allows you to define symbols which can be used inside the HLSL shadercode to alter the behaviour (through #ifdef or #if clauses). Definitions areseparated by ’;’ or ’,’ and may optionally have a ’=’ operator within them tospecify a definition value. Those without an ’=’ will implicitly have a definitionof 1.

column major matrices <true|false>The default for this option is ’true’ so that OGRE passes matrices auto-boundmatrices in a form where mul(m,v) works. Setting this option to false does2 things - it transpose auto-bound 4x4 matrices and also sets the /Zpr(row-major) option on the shader compilation. This means you can still usemul(m,v), but the matrix layout is row-major instead. This is only useful ifyou need to use bone matrices (float3x4) in a shader since it saves a float4constant for every bone involved.

optimisation level <opt>Set the optimisation level, which can be one of ’default’, ’none’, ’0’, ’1’, ’2’, or’3’. This corresponds to the /O parameter of fxc.exe, except that in ’default’mode, optimisation is disabled in debug mode and set to 1 in release mode(fxc.exe uses 1 all the time). Unsurprisingly the default value is ’default’. Youmay want to change this if you want to tweak the optimisation, for exampleif your shader gets so complex that it will not longer compile without someminimum level of optimisation.

3.1.7 OpenGL GLSL

OpenGL GLSL has a similar language syntax to HLSL but is tied to the OpenGL API. Theare a few benefits over Cg in that it only requires the OpenGL render system plugin, notany additional plugins. Declaring a OpenGL GLSL program is similar to Cg but simpler.Here’s an example:


vertex_program myGLSLVertexProgram glsl{

source myGLSLVertexProgram.txt}

In GLSL, no entry point needs to be defined since it is always ’main()’ and there is notarget definition since GLSL source is compiled into native GPU code and not intermediateassembly.

GLSL supports the use of modular shaders. This means you can write GLSL externalfunctions that can be used in multiple shaders.

vertex_program myExternalGLSLFunction1 glsl{

source myExternalGLSLfunction1.txt}

vertex_program myExternalGLSLFunction2 glsl{

source myExternalGLSLfunction2.txt}

vertex_program myGLSLVertexProgram1 glsl{

source myGLSLfunction.txtattach myExternalGLSLFunction1 myExternalGLSLFunction2

}

vertex_program myGLSLVertexProgram2 glsl{

source myGLSLfunction.txtattach myExternalGLSLFunction1

}

External GLSL functions are attached to the program that needs them by using ’attach’and including the names of all external programs required on the same line separated byspaces. This can be done for both vertex and fragment programs.

GLSL Texture Samplers

To pass texture unit index values from the material script to texture samplers in glsl use’int’ type named parameters. See the example below:

excerpt from GLSL example.frag source:

varying vec2 UV;uniform sampler2D diffuseMap;

void main(void)


{gl_FragColor = texture2D(diffuseMap, UV);

}

In material script:fragment_program myFragmentShader glsl{source example.frag

}

material exampleGLSLTexturing{technique{

pass{fragment_program_ref myFragmentShader{param_named diffuseMap int 0

}

texture_unit{

texture myTexture.jpg 2d}

}}

}

An index value of 0 refers to the first texture unit in the pass, an index value of 1 refersto the second unit in the pass and so on.

Matrix parameters

Here are some examples of passing matrices to GLSL mat2, mat3, mat4 uniforms:material exampleGLSLmatrixUniforms{technique matrix_passing{

pass examples{vertex_program_ref myVertexShader{

// mat4 uniformparam_named OcclusionMatrix matrix4x4 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0// orparam_named ViewMatrix float16 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0


// mat3param_named TextRotMatrix float9 1 0 0 0 1 0 0 0 1

}

fragment_program_ref myFragmentShader{

// mat2 uniformparam_named skewMatrix float4 0.5 0 -0.5 1.0

}

}}

}

Accessing OpenGL states in GLSL

GLSL can access most of the GL states directly so you do not need to pass these statesthrough [param named auto], page 93 in the material script. This includes lights, materialstate, and all the matrices used in the openGL state i.e. model view matrix, worldviewprojection matrix etc.

Binding vertex attributes

GLSL natively supports automatic binding of the most common incoming per-vertex at-tributes (e.g. gl Vertex, gl Normal, gl MultiTexCoord0 etc). However, there are somewhich are not automatically bound, which must be declared in the shader using the ’at-tribute <type> <name>’ syntax, and the vertex data bound to it by Ogre.

In addition to the built in attributes described in section 7.3 of the GLSL manual,Ogre supports a number of automatically bound custom vertex attributes. There are somedrivers that do not behave correctly when mixing built-in vertex attributes like gl Normaland custom vertex attributes, so for maximum compatibility you may well wish to use allcustom attributes in shaders where you need at least one (e.g. for skeletal animation).

vertex Binds VES POSITION, declare as ’attribute vec4 vertex;’.

normal Binds VES NORMAL, declare as ’attribute vec3 normal;’.

colour Binds VES DIFFUSE, declare as ’attribute vec4 colour;’.

secondary colourBinds VES SPECULAR, declare as ’attribute vec4 secondary colour;’.

uv0 - uv7 Binds VES TEXTURE COORDINATES, declare as ’attribute vec4 uv0;’. Notethat uv6 and uv7 share attributes with tangent and binormal respectively socannot both be present.

tangent Binds VES TANGENT, declare as ’attribute vec3 tangent;’.


binormal Binds VES BINORMAL, declare as ’attribute vec3 binormal;’.

blendIndicesBinds VES BLEND INDICES, declare as ’attribute vec4 blendIndices;’.

blendWeightsBinds VES BLEND WEIGHTS, declare as ’attribute vec4 blendWeights;’.

Preprocessor definitions

GLSL supports using preprocessor definitions in your code - some are defined by the imple-mentation, but you can also define your own, say in order to use the same source code fora few different variants of the same technique. In order to use this feature, include prepro-cessor conditions in your GLSL code, of the kind #ifdef SYMBOL, #if SYMBOL==2 etc.Then in your program definition, use the ’preprocessor defines’ option, following it with astring if definitions. Definitions are separated by ’;’ or ’,’ and may optionally have a ’=’operator within them to specify a definition value. Those without an ’=’ will implicitlyhave a definition of 1. For example:

// in your GLSL

#ifdef CLEVERTECHNIQUE// some clever stuff here

#else// normal technique

#endif

#if NUM_THINGS==2// Some specific code

#else// something else

#endif

// in your program definitionpreprocessor_defines CLEVERTECHNIQUE,NUMTHINGS=2

This way you can use the same source code but still include small variations, each onedefined as a different Ogre program name but based on the same source code.

GLSL Geometry shader specification

GLSL allows the same shader to run on different types of geometry primitives. In order toproperly link the shaders together, you have to specify which primitives it will receive asinput, which primitives it will emit and how many vertices a single run of the shader cangenerate. The GLSL geometry program definition requires three additional parameters :

input operation typeThe operation type of the geometry that the shader will receive. Canbe ’point list’, ’line list’, ’line strip’, ’triangle list’, ’triangle strip’ or’triangle fan’.


output operation typeThe operation type of the geometry that the shader will emit. Can be’point list’, ’line strip’ or ’triangle strip’.

max output verticesThe maximum number of vertices that the shader can emit. There is an upperlimit for this value, it is exposed in the render system capabilities.

For example:geometry_program Ogre/GPTest/Swizzle_GP_GLSL glsl{

source SwizzleGP.glslinput_operation_type triangle_listoutput_operation_type line_stripmax_output_vertices 6

}

3.1.8 Unified High-level Programs

As mentioned above, it can often be useful to write both HLSL and GLSL programs tospecifically target each platform, but if you do this via multiple material techniques thiscan cause a bloated material definition when the only difference is the program language.Well, there is another option. You can ’wrap’ multiple programs in a ’unified’ programdefinition, which will automatically choose one of a series of ’delegate’ programs dependingon the rendersystem and hardware support.vertex_program myVertexProgram unified{

delegate realProgram1delegate realProgram2... etc

}

This works for both vertex and fragment programs, and you can list as many delegatesas you like - the first one to be supported by the current rendersystem & hardware willbe used as the real program. This is almost like a mini-technique system, but for a singleprogram and with a much tighter purpose. You can only use this where the programs takeall the same inputs, particularly textures and other pass / sampler state. Where the onlydifference between the programs is the language (or possibly the target in HLSL - you caninclude multiple HLSL programs with different targets in a single unified program too if youwant, or indeed any number of other high-level programs), this can become a very powerfulfeature. For example, without this feature here’s how you’d have to define a programmablematerial which supported HLSL and GLSL:vertex_program myVertexProgramHLSL hlsl{

source prog.hlslentry_point main_vptarget vs_2_0

}fragment_program myFragmentProgramHLSL hlsl


{source prog.hlslentry_point main_fptarget ps_2_0

}vertex_program myVertexProgramGLSL glsl{

source prog.vert}fragment_program myFragmentProgramGLSL glsl{

source prog.fragdefault_params{

param_named tex int 0}

}material SupportHLSLandGLSLwithoutUnified{

// HLSL techniquetechnique{

pass{

vertex_program_ref myVertexProgramHLSL{

param_named_auto worldViewProj world_view_proj_matrixparam_named_auto lightColour light_diffuse_colour 0param_named_auto lightSpecular light_specular_colour 0param_named_auto lightAtten light_attenuation 0

}fragment_program_ref myFragmentProgramHLSL{}

}}// GLSL techniquetechnique{

pass{

vertex_program_ref myVertexProgramHLSL{



}fragment_program_ref myFragmentProgramHLSL{}

}}

}

And that’s a really small example. Everything you added to the HLSL technique, you’dhave to duplicate in the GLSL technique too. So instead, here’s how you’d do it with unifiedprogram definitions:

vertex_program myVertexProgramHLSL hlsl{

source prog.hlslentry_point main_vptarget vs_2_0

}fragment_program myFragmentProgramHLSL hlsl{

source prog.hlslentry_point main_fptarget ps_2_0

}vertex_program myVertexProgramGLSL glsl{

source prog.vert}fragment_program myFragmentProgramGLSL glsl{

source prog.fragdefault_params{

param_named tex int 0}

}// Unified definitionvertex_program myVertexProgram unified{

delegate myVertexProgramGLSLdelegate myVertexProgramHLSL

}fragment_program myFragmentProgram unified{

delegate myFragmentProgramGLSLdelegate myFragmentProgramHLSL

}material SupportHLSLandGLSLwithUnified


{// HLSL techniquetechnique{

pass{

vertex_program_ref myVertexProgram{


}fragment_program_ref myFragmentProgram{}

}}

}

At runtime, when myVertexProgram or myFragmentProgram are used, OGRE automat-ically picks a real program to delegate to based on what’s supported on the current hardware/ rendersystem. If none of the delegates are supported, the entire technique referencing theunified program is marked as unsupported and the next technique in the material is checkedfro fallback, just like normal. As your materials get larger, and you find you need to supportHLSL and GLSL specifically (or need to write multiple interface-compatible versions of aprogram for whatever other reason), unified programs can really help reduce duplication.

3.1.9 Using Vertex/Geometry/Fragment Programs in a Pass

Within a pass section of a material script, you can reference a vertex, geometry and / or afragment program which is been defined in a .program script (See Section 3.1.4 [DeclaringVertex/Geometry/Fragment Programs], page 63). The programs are defined separatelyfrom the usage of them in the pass, since the programs are very likely to be reused betweenmany separate materials, probably across many different .material scripts, so this approachlets you define the program only once and use it many times.

As well as naming the program in question, you can also provide parameters to it. Here’sa simple example:vertex_program_ref myVertexProgram{

param_indexed_auto 0 worldviewproj_matrixparam_indexed 4 float4 10.0 0 0 0

}

In this example, we bind a vertex program called ’myVertexProgram’ (which will bedefined elsewhere) to the pass, and give it 2 parameters, one is an ’auto’ parameter, meaningwe do not have to supply a value as such, just a recognised code (in this case it’s the


world/view/projection matrix which is kept up to date automatically by Ogre). The secondparameter is a manually specified parameter, a 4-element float. The indexes are describedlater.

The syntax of the link to a vertex program and a fragment or geometry program areidentical, the only difference is that ’fragment program ref’ and ’geometry program ref’are used respectively instead of ’vertex program ref’.

For many situations vertex, geometry and fragment programs are associated with eachother in a pass but this is not cast in stone. You could have a vertex program that canbe used by several different fragment programs. Another situation that arises is that youcan mix fixed pipeline and programmable pipeline (shaders) together. You could use thenon-programable vertex fixed function pipeline and then provide a fragment program refin a pass i.e. there would be no vertex program ref section in the pass. The fragmentprogram referenced in the pass must meet the requirements as defined in the related APIin order to read from the outputs of the vertex fixed pipeline. You could also just have avertex program that outputs to the fragment fixed function pipeline.

The requirements to read from or write to the fixed function pipeline are similar betweenrendering API’s (DirectX and OpenGL) but how its actually done in each type of shader(vertex, geometry or fragment) depends on the shader language. For HLSL (DirectXAPI) and associated asm consult MSDN at http://msdn.microsoft.com/library/.For GLSL (OpenGL), consult section 7.6 of the GLSL spec 1.1 available athttp://developer.3dlabs.com/documents/index.htm. The built in varying variablesprovided in GLSL allow your program to read/write to the fixed function pipeline varyings.For Cg consult the Language Profiles section in CgUsersManual.pdf that comes with theCg Toolkit available at http://developer.nvidia.com/object/cg_toolkit.html. ForHLSL and Cg its the varying bindings that allow your shader programs to read/write tothe fixed function pipeline varyings.

Parameter specification

Parameters can be specified using one of 4 commands as shown below. The same syntax isused whether you are defining a parameter just for this particular use of the program, orwhen specifying the [Default Program Parameters], page 66. Parameters set in the specificuse of the program override the defaults.• [param indexed], page 80• [param indexed auto], page 81• [param named], page 92• [param named auto], page 93• [shared params ref], page 93

http://msdn.microsoft.com/library/

http://developer.3dlabs.com/documents/index.htm

http://developer.nvidia.com/object/cg_toolkit.html


param indexed

This command sets the value of an indexed parameter.

format: param indexed <index> <type> <value>

example: param indexed 0 float4 10.0 0 0 0

The ’index’ is simply a number representing the position in the parameter list whichthe value should be written, and you should derive this from your program definition. Theindex is relative to the way constants are stored on the card, which is in 4-element blocks.For example if you defined a float4 parameter at index 0, the next index would be 1. If youdefined a matrix4x4 at index 0, the next usable index would be 4, since a 4x4 matrix takesup 4 indexes.

The value of ’type’ can be float4, matrix4x4, float<n>, int4, int<n>. Note that ’int’parameters are only available on some more advanced program syntaxes, check the D3D orGL vertex / fragment program documentation for full details. Typically the most usefulones will be float4 and matrix4x4. Note that if you use a type which is not a multiple of4, then the remaining values up to the multiple of 4 will be filled with zeroes for you (sinceGPUs always use banks of 4 floats per constant even if only one is used).

’value’ is simply a space or tab-delimited list of values which can be converted into thetype you have specified.

param indexed auto

This command tells Ogre to automatically update a given parameter with a derived value.This frees you from writing code to update program parameters every frame when they arealways changing.

format: param indexed auto <index> <value code> <extra params>

example: param indexed auto 0 worldviewproj matrix

’index’ has the same meaning as [param indexed], page 80; note this time you do nothave to specify the size of the parameter because the engine knows this already. In theexample, the world/view/projection matrix is being used so this is implicitly a matrix4x4.


’value code’ is one of a list of recognised values:

world matrixThe current world matrix.

inverse world matrixThe inverse of the current world matrix.

transpose world matrixThe transpose of the world matrix

inverse transpose world matrixThe inverse transpose of the world matrix

world matrix array 3x4An array of world matrices, each represented as only a 3x4 matrix (3 rowsof 4columns) usually for doing hardware skinning. You should make enoughentries available in your vertex program for the number of bones in use, ie anarray of numBones*3 float4’s.

view matrixThe current view matrix.

inverse view matrixThe inverse of the current view matrix.

transpose view matrixThe transpose of the view matrix

inverse transpose view matrixThe inverse transpose of the view matrix

projection matrixThe current projection matrix.

inverse projection matrixThe inverse of the projection matrix

transpose projection matrixThe transpose of the projection matrix

inverse transpose projection matrixThe inverse transpose of the projection matrix

worldview matrixThe current world and view matrices concatenated.

inverse worldview matrixThe inverse of the current concatenated world and view matrices.

transpose worldview matrixThe transpose of the world and view matrices

inverse transpose worldview matrixThe inverse transpose of the current concatenated world and view matrices.


viewproj matrixThe current view and projection matrices concatenated.

inverse viewproj matrixThe inverse of the view & projection matrices

transpose viewproj matrixThe transpose of the view & projection matrices

inverse transpose viewproj matrixThe inverse transpose of the view & projection matrices

worldviewproj matrixThe current world, view and projection matrices concatenated.

inverse worldviewproj matrixThe inverse of the world, view and projection matrices

transpose worldviewproj matrixThe transpose of the world, view and projection matrices

inverse transpose worldviewproj matrixThe inverse transpose of the world, view and projection matrices

texture matrixThe transform matrix of a given texture unit, as it would usually be seen in thefixed-function pipeline. This requires an index in the ’extra params’ field, andrelates to the ’nth’ texture unit of the pass in question. NB if the given indexexceeds the number of texture units available for this pass, then the parameterwill be set to Matrix4::IDENTITY.

render target flippingThe value use to adjust transformed y position if bypassed projection matrixtransform. It’s -1 if the render target requires texture flipping, +1 otherwise.

vertex windingIndicates what vertex winding mode the render state is in at this point; +1 forstandard, -1 for inverted (e.g. when processing reflections).

light diffuse colourThe diffuse colour of a given light; this requires an index in the ’extra params’field, and relates to the ’nth’ closest light which could affect this object (i.e. 0refers to the closest light - note that directional lights are always first in the listand always present). NB if there are no lights this close, then the parameterwill be set to black.

light specular colourThe specular colour of a given light; this requires an index in the ’extra params’field, and relates to the ’nth’ closest light which could affect this object (i.e.0 refers to the closest light). NB if there are no lights this close, then theparameter will be set to black.

light attenuationA float4 containing the 4 light attenuation variables for a given light. Thisrequires an index in the ’extra params’ field, and relates to the ’nth’ closest


light which could affect this object (i.e. 0 refers to the closest light). NBif there are no lights this close, then the parameter will be set to all zeroes.The order of the parameters is range, constant attenuation, linear attenuation,quadric attenuation.

spotlight paramsA float4 containing the 3 spotlight parameters and a control value. The order ofthe parameters is cos(inner angle /2 ), cos(outer angle / 2), falloff, and the finalw value is 1.0f. For non-spotlights the value is float4(1,0,0,1). This requiresan index in the ’extra params’ field, and relates to the ’nth’ closest light whichcould affect this object (i.e. 0 refers to the closest light). If there are less lightsthan this, the details are like a non-spotlight.

light positionThe position of a given light in world space. This requires an index in the’extra params’ field, and relates to the ’nth’ closest light which could affect thisobject (i.e. 0 refers to the closest light). NB if there are no lights this close,then the parameter will be set to all zeroes. Note that this property will workwith all kinds of lights, even directional lights, since the parameter is set asa 4D vector. Point lights will be (pos.x, pos.y, pos.z, 1.0f) whilst directionallights will be (-dir.x, -dir.y, -dir.z, 0.0f). Operations like dot products will workconsistently on both.

light directionThe direction of a given light in world space. This requires an index in the’extra params’ field, and relates to the ’nth’ closest light which could affect thisobject (i.e. 0 refers to the closest light). NB if there are no lights this close,then the parameter will be set to all zeroes. DEPRECATED - this propertyonly works on directional lights, and we recommend that you use light positioninstead since that returns a generic 4D vector.

light position object spaceThe position of a given light in object space (i.e. when the object is at (0,0,0)).This requires an index in the ’extra params’ field, and relates to the ’nth’ closestlight which could affect this object (i.e. 0 refers to the closest light). NB if thereare no lights this close, then the parameter will be set to all zeroes. Note thatthis property will work with all kinds of lights, even directional lights, since theparameter is set as a 4D vector. Point lights will be (pos.x, pos.y, pos.z, 1.0f)whilst directional lights will be (-dir.x, -dir.y, -dir.z, 0.0f). Operations like dotproducts will work consistently on both.

light direction object spaceThe direction of a given light in object space (i.e. when the object is at (0,0,0)).This requires an index in the ’extra params’ field, and relates to the ’nth’ closestlight which could affect this object (i.e. 0 refers to the closest light). NBif there are no lights this close, then the parameter will be set to all zeroes.DEPRECATED, except for spotlights - for directional lights we recommendthat you use light position object space instead since that returns a generic4D vector.


light distance object spaceThe distance of a given light from the centre of the object - this is a usefulapproximation to per-vertex distance calculations for relatively small objects.This requires an index in the ’extra params’ field, and relates to the ’nth’ closestlight which could affect this object (i.e. 0 refers to the closest light). NB if thereare no lights this close, then the parameter will be set to all zeroes.

light position view spaceThe position of a given light in view space (i.e. when the camera is at (0,0,0)).This requires an index in the ’extra params’ field, and relates to the ’nth’ closestlight which could affect this object (i.e. 0 refers to the closest light). NB if thereare no lights this close, then the parameter will be set to all zeroes. Note thatthis property will work with all kinds of lights, even directional lights, since theparameter is set as a 4D vector. Point lights will be (pos.x, pos.y, pos.z, 1.0f)whilst directional lights will be (-dir.x, -dir.y, -dir.z, 0.0f). Operations like dotproducts will work consistently on both.

light direction view spaceThe direction of a given light in view space (i.e. when the camera is at (0,0,0)).This requires an index in the ’extra params’ field, and relates to the ’nth’closest light which could affect this object (i.e. 0 refers to the closest light).NB if there are no lights this close, then the parameter will be set to all zeroes.DEPRECATED, except for spotlights - for directional lights we recommendthat you use light position view space instead since that returns a generic 4Dvector.

light powerThe ’power’ scaling for a given light, useful in HDR rendering. This requiresan index in the ’extra params’ field, and relates to the ’nth’ closest light whichcould affect this object (i.e. 0 refers to the closest light).

light diffuse colour power scaledAs light diffuse colour, except the RGB channels of the passed colour have beenpre-scaled by the light’s power scaling as given by light power.

light specular colour power scaledAs light specular colour, except the RGB channels of the passed colour havebeen pre-scaled by the light’s power scaling as given by light power.

light numberWhen rendering, there is generally a list of lights available for use by all of thepasses for a given object, and those lights may or may not be referenced inone or more passes. Sometimes it can be useful to know where in that overalllist a given light light (as seen from a pass) is. For example if you use iterateonce per light, the pass always sees the light as index 0, but in each iterationthe actual light referenced is different. This binding lets you pass through theactual index of the light in that overall list. You just need to give it a parameterof the pass-relative light number and it will map it to the overall list index.


light diffuse colour arrayAs light diffuse colour, except that this populates an array of parameters witha number of lights, and the ’extra params’ field refers to the number of ’nthclosest’ lights to be processed. This parameter is not compatible with light-based pass iteration options but can be used for single-pass lighting.

light specular colour arrayAs light specular colour, except that this populates an array of parameterswith a number of lights, and the ’extra params’ field refers to the number of’nth closest’ lights to be processed. This parameter is not compatible withlight-based pass iteration options but can be used for single-pass lighting.

light diffuse colour power scaled arrayAs light diffuse colour power scaled, except that this populates an array ofparameters with a number of lights, and the ’extra params’ field refers to thenumber of ’nth closest’ lights to be processed. This parameter is not compatiblewith light-based pass iteration options but can be used for single-pass lighting.

light specular colour power scaled arrayAs light specular colour power scaled, except that this populates an array ofparameters with a number of lights, and the ’extra params’ field refers to thenumber of ’nth closest’ lights to be processed. This parameter is not compatiblewith light-based pass iteration options but can be used for single-pass lighting.

light attenuation arrayAs light attenuation, except that this populates an array of parameters witha number of lights, and the ’extra params’ field refers to the number of ’nthclosest’ lights to be processed. This parameter is not compatible with light-based pass iteration options but can be used for single-pass lighting.

spotlight params arrayAs spotlight params, except that this populates an array of parameters witha number of lights, and the ’extra params’ field refers to the number of ’nthclosest’ lights to be processed. This parameter is not compatible with light-based pass iteration options but can be used for single-pass lighting.

light position arrayAs light position, except that this populates an array of parameters with anumber of lights, and the ’extra params’ field refers to the number of ’nthclosest’ lights to be processed. This parameter is not compatible with light-based pass iteration options but can be used for single-pass lighting.

light direction arrayAs light direction, except that this populates an array of parameters with anumber of lights, and the ’extra params’ field refers to the number of ’nthclosest’ lights to be processed. This parameter is not compatible with light-based pass iteration options but can be used for single-pass lighting.

light position object space arrayAs light position object space, except that this populates an array of parame-ters with a number of lights, and the ’extra params’ field refers to the number


of ’nth closest’ lights to be processed. This parameter is not compatible withlight-based pass iteration options but can be used for single-pass lighting.

light direction object space arrayAs light direction object space, except that this populates an array of param-eters with a number of lights, and the ’extra params’ field refers to the numberof ’nth closest’ lights to be processed. This parameter is not compatible withlight-based pass iteration options but can be used for single-pass lighting.

light distance object space arrayAs light distance object space, except that this populates an array of parame-ters with a number of lights, and the ’extra params’ field refers to the numberof ’nth closest’ lights to be processed. This parameter is not compatible withlight-based pass iteration options but can be used for single-pass lighting.

light position view space arrayAs light position view space, except that this populates an array of parameterswith a number of lights, and the ’extra params’ field refers to the number of’nth closest’ lights to be processed. This parameter is not compatible withlight-based pass iteration options but can be used for single-pass lighting.

light direction view space arrayAs light direction view space, except that this populates an array of parame-ters with a number of lights, and the ’extra params’ field refers to the numberof ’nth closest’ lights to be processed. This parameter is not compatible withlight-based pass iteration options but can be used for single-pass lighting.

light power arrayAs light power, except that this populates an array of parameters with a num-ber of lights, and the ’extra params’ field refers to the number of ’nth clos-est’ lights to be processed. This parameter is not compatible with light-basedpass iteration options but can be used for single-pass lighting.

light countThe total number of lights active in this pass.

light casts shadowsSets an integer parameter to 1 if the given light casts shadows, 0 otherwise,Requires a light index parameter.

ambient light colourThe colour of the ambient light currently set in the scene.

surface ambient colourThe ambient colour reflectance properties of the pass (See [ambient], page 25).This allows you access to fixed-function pipeline property handily.

surface diffuse colourThe diffuse colour reflectance properties of the pass (See [diffuse], page 26).This allows you access to fixed-function pipeline property handily.

surface specular colourThe specular colour reflectance properties of the pass (See [specular], page 26).This allows you access to fixed-function pipeline property handily.


surface emissive colourThe amount of self-illumination of the pass (See [emissive], page 27). Thisallows you access to fixed-function pipeline property handily.

surface shininessThe shininess of the pass, affecting the size of specular highlights (See [specular],page 26). This allows you bind to fixed-function pipeline property handily.

derived ambient light colourThe derived ambient light colour, with ’r’, ’g’, ’b’ components filled with prod-uct of surface ambient colour and ambient light colour, respectively, and ’a’component filled with surface ambient alpha component.

derived scene colourThe derived scene colour, with ’r’, ’g’ and ’b’ components filled with sum ofderived ambient light colour and surface emissive colour, respectively, and ’a’component filled with surface diffuse alpha component.

derived light diffuse colourThe derived light diffuse colour, with ’r’, ’g’ and ’b’ components filled with prod-uct of surface diffuse colour, light diffuse colour and light power, respectively,and ’a’ component filled with surface diffuse alpha component. This requiresan index in the ’extra params’ field, and relates to the ’nth’ closest light whichcould affect this object (i.e. 0 refers to the closest light).

derived light specular colourThe derived light specular colour, with ’r’, ’g’ and ’b’ components filled withproduct of surface specular colour and light specular colour, respectively, and’a’ component filled with surface specular alpha component. This requires anindex in the ’extra params’ field, and relates to the ’nth’ closest light whichcould affect this object (i.e. 0 refers to the closest light).

derived light diffuse colour arrayAs derived light diffuse colour, except that this populates an array of parame-ters with a number of lights, and the ’extra params’ field refers to the numberof ’nth closest’ lights to be processed. This parameter is not compatible withlight-based pass iteration options but can be used for single-pass lighting.

derived light specular colour arrayAs derived light specular colour, except that this populates an array of param-eters with a number of lights, and the ’extra params’ field refers to the numberof ’nth closest’ lights to be processed. This parameter is not compatible withlight-based pass iteration options but can be used for single-pass lighting.

fog colour The colour of the fog currently set in the scene.

fog paramsThe parameters of the fog currently set in the scene. Packed as (exp density,linear start, linear end, 1.0 / (linear end - linear start)).

camera positionThe current cameras position in world space.


camera position object spaceThe current cameras position in object space (i.e. when the object is at (0,0,0)).

lod camera positionThe current LOD camera position in world space. A LOD camera is a separatecamera associated with the rendering camera which allows LOD calculations tobe calculated separately. The classic example is basing the LOD of the shadowtexture render on the position of the main camera, not the shadow camera.

lod camera position object spaceThe current LOD camera position in object space (i.e. when the object is at(0,0,0)).

time The current time, factored by the optional parameter (or 1.0f if not supplied).

time 0 x Single float time value, which repeats itself based on "cycle time" given as an’extra params’ field

costime 0 xCosine of time 0 x

sintime 0 xSine of time 0 x

tantime 0 xTangent of time 0 x

time 0 x packed4-element vector of time0 x, sintime0 x, costime0 x, tantime0 x

time 0 1 As time0 x but scaled to [0..1]

costime 0 1As costime0 x but scaled to [0..1]

sintime 0 1As sintime0 x but scaled to [0..1]

tantime 0 1As tantime0 x but scaled to [0..1]

time 0 1 packedAs time0 x packed but all values scaled to [0..1]

time 0 2piAs time0 x but scaled to [0..2*Pi]

costime 0 2piAs costime0 x but scaled to [0..2*Pi]

sintime 0 2piAs sintime0 x but scaled to [0..2*Pi]

tantime 0 2piAs tantime0 x but scaled to [0..2*Pi]

time 0 2pi packedAs time0 x packed but scaled to [0..2*Pi]


frame timeThe current frame time, factored by the optional parameter (or 1.0f if notsupplied).

fps The current frames per second

viewport widthThe current viewport width in pixels

viewport heightThe current viewport height in pixels

inverse viewport width1.0/the current viewport width in pixels

inverse viewport height1.0/the current viewport height in pixels

viewport size4-element vector of viewport width, viewport height, inverse viewport width,inverse viewport height

texel offsetsProvides details of the rendersystem-specific texture coordinate offsets requiredto map texels onto pixels. float4(horizontalOffset, verticalOffset, horizontalOff-set / viewport width, verticalOffset / viewport height).

view directionView direction vector in object space

view side vectorView local X axis

view up vectorView local Y axis

fov Vertical field of view, in radians

near clip distanceNear clip distance, in world units

far clip distanceFar clip distance, in world units (may be 0 for infinite view projection)

texture viewproj matrixApplicable to vertex programs which have been specified as the ’shadow re-ceiver’ vertex program alternative, or where a texture unit is marked as con-tent type shadow; this provides details of the view/projection matrix for thecurrent shadow projector. The optional ’extra params’ entry specifies whichlight the projector refers to (for the case of content type shadow where morethan one shadow texture may be present in a single pass), where 0 is the defaultand refers to the first light referenced in this pass.

texture viewproj matrix arrayAs texture viewproj matrix, except an array of matrices is passed, up to thenumber that you specify as the ’extra params’ value.


texture worldviewproj matrixAs texture viewproj matrix except it also includes the world matrix.

texture worldviewproj matrix arrayAs texture worldviewproj matrix, except an array of matrices is passed, up tothe number that you specify as the ’extra params’ value.

spotlight viewproj matrixProvides a view / projection matrix which matches the set up of a given spot-light (requires an ’extra params’ entry to indicate the light index, which mustbe a spotlight). Can be used to project a texture from a given spotlight.

spotlight worldviewproj matrixAs spotlight viewproj matrix except it also includes the world matrix.

scene depth rangeProvides information about the depth range as viewed from the current camerabeing used to render. Provided as float4(minDepth, maxDepth, depthRange, 1/ depthRange).

shadow scene depth rangeProvides information about the depth range as viewed from the shadow camerarelating to a selected light. Requires a light index parameter. Provided asfloat4(minDepth, maxDepth, depthRange, 1 / depthRange).

shadow colourThe shadow colour (for modulative shadows) as set via SceneMan-ager::setShadowColour.

shadow extrusion distanceThe shadow extrusion distance as determined by the range of a non-directionallight or set via SceneManager::setShadowDirectionalLightExtrusionDistance fordirectional lights.

texture sizeProvides texture size of the selected texture unit. Requires a texture unit indexparameter. Provided as float4(width, height, depth, 1). For 2D-texture, depthsets to 1, for 1D-texture, height and depth sets to 1.

inverse texture sizeProvides inverse texture size of the selected texture unit. Requires a textureunit index parameter. Provided as float4(1 / width, 1 / height, 1 / depth, 1).For 2D-texture, depth sets to 1, for 1D-texture, height and depth sets to 1.

packed texture sizeProvides packed texture size of the selected texture unit. Requires a textureunit index parameter. Provided as float4(width, height, 1 / width, 1 / height).For 3D-texture, depth is ignored, for 1D-texture, height sets to 1.

pass numberSets the active pass index number in a gpu parameter. The first pass in atechnique has an index of 0, the second an index of 1 and so on. This is usefulfor multipass shaders (i.e. fur or blur shader) that need to know what pass it is.


By setting up the auto parameter in a [Default Program Parameters], page 66list in a program definition, there is no requirement to set the pass numberparameter in each pass and lose track. (See [fur example], page 42)

pass iteration numberUseful for GPU programs that need to know what the current pass iterationnumber is. The first iteration of a pass is numbered 0. The last iterationnumber is one less than what is set for the pass iteration number. If a pass hasits iteration attribute set to 5 then the last iteration number (5th execution ofthe pass) is 4.(See [iteration], page 41)

animation parametricUseful for hardware vertex animation. For morph animation, sets the paramet-ric value (0..1) representing the distance between the first position keyframe(bound to positions) and the second position keyframe (bound to the first freetexture coordinate) so that the vertex program can interpolate between them.For pose animation, indicates a group of up to 4 parametric weight values ap-plying to a sequence of up to 4 poses (each one bound to x, y, z and w ofthe constant), one for each pose. The original positions are held in the usualposition buffer, and the offsets to take those positions to the pose where weight== 1.0 are in the first ’n’ free texture coordinates; ’n’ being determined by thevalue passed to includes pose animation. If more than 4 simultaneous poses arerequired, then you’ll need more than 1 shader constant to hold the parametricvalues, in which case you should use this binding more than once, referencing adifferent constant entry; the second one will contain the parametrics for poses5-8, the third for poses 9-12, and so on.

custom This allows you to map a custom parameter on an individual Renderable (seeRenderable::setCustomParameter) to a parameter on a GPU program. It re-quires that you complete the ’extra params’ field with the index that was usedin the Renderable::setCustomParameter call, and this will ensure that when-ever this Renderable is used, it will have it’s custom parameter mapped in. It’svery important that this parameter has been defined on all Renderables thatare assigned the material that contains this automatic mapping, otherwise theprocess will fail.

param named

This is the same as param indexed, but uses a named parameter instead of an index. Thiscan only be used with high-level programs which include parameter names; if you’re usingan assembler program then you have no choice but to use indexes. Note that you can useindexed parameters for high-level programs too, but it is less portable since if you reorderyour parameters in the high-level program the indexes will change.

format: param named <name> <type> <value>

example: param named shininess float4 10.0 0 0 0

The type is required because the program is not compiled and loaded when the material


script is parsed, so at this stage we have no idea what types the parameters are. Programsare only loaded and compiled when they are used, to save memory.

param named auto

This is the named equivalent of param indexed auto, for use with high-level programs.

Format: param named auto <name> <value code> <extra params>

Example: param named auto worldViewProj WORLDVIEWPROJ MATRIX

The allowed value codes and the meaning of extra params are detailed in[param indexed auto], page 81.

shared params ref

This option allows you to reference shared parameter sets as defined in [Declaring SharedParameters], page 66.

Format: shared params ref <shared set name>

Example: shared params ref mySharedParams

The only required parameter is a name, which must be the name of an already definedshared parameter set. All named parameters which are present in the program that arealso present in the shared parameter set will be linked, and the shared parameters used asif you had defined them locally. This is dependent on the definitions (type and array size)matching between the shared set and the program.

Shadows and Vertex Programs

When using shadows (See Chapter 7 [Shadows], page 180), the use of vertex programs canadd some additional complexities, because Ogre can only automatically deal with everythingwhen using the fixed-function pipeline. If you use vertex programs, and you are also usingshadows, you may need to make some adjustments.

If you use stencil shadows, then any vertex programs which do vertex deformation canbe a problem, because stencil shadows are calculated on the CPU, which does not haveaccess to the modified vertices. If the vertex program is doing standard skeletal animation,this is ok (see section above) because Ogre knows how to replicate the effect in software,but any other vertex deformation cannot be replicated, and you will either have to acceptthat the shadow will not reflect this deformation, or you should turn off shadows for thatobject.


If you use texture shadows, then vertex deformation is acceptable; however, when ren-dering the object into the shadow texture (the shadow caster pass), the shadow has to berendered in a solid colour (linked to the ambient colour). You must therefore provide analternative vertex program, so Ogre provides you with a way of specifying one to use whenrendering the caster. Basically you link an alternative vertex program, using exactly thesame syntax as the original vertex program link:shadow_caster_vertex_program_ref myShadowCasterVertexProgram{

param_indexed_auto 0 worldviewproj_matrixparam_indexed_auto 4 ambient_light_colour

}

When rendering a shadow caster, Ogre will automatically use the alternate program.You can bind the same or different parameters to the program - the most important thingis that you bind ambiend light colour, since this determines the colour of the shadow inmodulative texture shadows. If you don’t supply an alternate program, Ogre will fall backon a fixed-function material which will not reflect any vertex deformation you do in yourvertex program.

In addition, when rendering the shadow receivers with shadow textures, Ogre needs toproject the shadow texture. It does this automatically in fixed function mode, but if thereceivers use vertex programs, they need to have a shadow receiver program which does theusual vertex deformation, but also generates projective texture coordinates. The additionalprogram linked into the pass like this:shadow_receiver_vertex_program_ref myShadowReceiverVertexProgram{

param_indexed_auto 0 worldviewproj_matrixparam_indexed_auto 4 texture_viewproj_matrix

}

For the purposes of writing this alternate program, there is an automatic parameterbinding of ’texture viewproj matrix’ which provides the program with texture projectionparameters. The vertex program should do it’s normal vertex processing, and generatetexture coordinates using this matrix and place them in texture coord sets 0 and 1, sincesome shadow techniques use 2 texture units. The colour of the vertices output by this vertexprogram must always be white, so as not to affect the final colour of the rendered shadow.

When using additive texture shadows, the shadow pass render is actually the lightingrender, so if you perform any fragment program lighting you also need to pull in a customfragment program. You use the shadow receiver fragment program ref for this:shadow_receiver_fragment_program_ref myShadowReceiverFragmentProgram{

param_named_auto lightDiffuse light_diffuse_colour 0


}

You should pass the projected shadow coordinates from the custom vertex program. Asfor textures, texture unit 0 will always be the shadow texture. Any other textures whichyou bind in your pass will be carried across too, but will be moved up by 1 unit to makeroom for the shadow texture. Therefore your shadow receiver fragment program is likelyto be the same as the bare lighting pass of your normal material, except that you insert anextra texture sampler at index 0, which you will use to adjust the result by (modulatingdiffuse and specular components).

3.1.10 Vertex Texture Fetch

Introduction

More recent generations of video card allow you to perform a read from a texture in thevertex program rather than just the fragment program, as is traditional. This allows youto, for example, read the contents of a texture and displace vertices based on the intensityof the colour contained within.

Declaring the use of vertex texture fetching

Since hardware support for vertex texture fetching is not ubiquitous, you should use theuses vertex texture fetch (See 〈undefined〉 [Vertex texture fetching in vertex programs],page 〈undefined〉) directive when declaring your vertex programs which use vertex textures,so that if it is not supported, technique fallback can be enabled. This is not strictly necessaryfor DirectX-targeted shaders, since vertex texture fetching is only supported in vs 3 0, whichcan be stated as a required syntax in your shader definition, but for OpenGL (GLSL), thereare cards which support GLSL but not vertex textures, so you should be explicit aboutyour need for them.

Render system texture binding differences

Unfortunately the method for binding textures so that they are available to a vertex programis not well standardised. As at the time of writing, Shader Model 3.0 (SM3.0) hardwareunder DirectX9 include 4 separate sampler bindings for the purposes of vertex textures.OpenGL, on the other hand, is able to access vertex textures in GLSL (and in assemblerthrough NV vertex program 3, although this is less popular), but the textures are sharedwith the fragment pipeline. I expect DirectX to move to the GL model with the advent ofDirectX10, since a unified shader architecture implies sharing of texture resources betweenthe two stages. As it is right now though, we’re stuck with an inconsistent situation.

To reflect this, you should use the [binding type], page 51 attribute in a texture unitto indicate which unit you are targeting with your texture - ’fragment’ (the default) or’vertex’. For render systems that don’t have separate bindings, this actually does nothing.But for those that do, it will ensure your texture gets bound to the right processing unit.

Note that whilst DirectX9 has separate bindings for the vertex and fragment pipelines,binding a texture to the vertex processing unit still uses up a ’slot’ which is then not available


for use in the fragment pipeline. I didn’t manage to find this documented anywhere, butthe nVidia samples certainly avoid binding a texture to the same index on both vertexand fragment units, and when I tried to do it, the texture did not appear correctly in thefragment unit, whilst it did as soon as I moved it into the next unit.

Texture format limitations

Again as at the time of writing, the types of texture you can use in a vertex program arelimited to 1- or 4-component, full precision floating point formats. In code that equates toPF FLOAT32 R or PF FLOAT32 RGBA. No other formats are supported. In addition,the textures must be regular 2D textures (no cube or volume maps) and mipmapping andfiltering is not supported, although you can perform filtering in your vertex program if youwish by sampling multiple times.

Hardware limitations

As at the time of writing (early Q3 2006), ATI do not support texture fetch in their currentcrop of cards (Radeon X1n00). nVidia do support it in both their 6n00 and 7n00 range.ATI support an alternative called ’Render to Vertex Buffer’, but this is not standardisedat this time and is very much different in its implementation, so cannot be considered tobe a drop-in replacement. This is the case even though the Radeon X1n00 cards claim tosupport vs 3 0 (which requires vertex texture fetch).

3.1.11 Script Inheritence

When creating new script objects that are only slight variations of another object, it’s goodto avoid copying and pasting between scripts. Script inheritence lets you do this; in thissection we’ll use material scripts as an example, but this applies to all scripts parsed withthe script compilers in Ogre 1.6 onwards.

For example, to make a new material that is based on one previously defined, add acolon : after the new material name followed by the name of the material that is to becopied.

Format: material <NewUniqueChildName> : <ReferanceParentMaterial>

The only caveat is that a parent material must have been defined/parsed prior to thechild material script being parsed. The easiest way to achieve this is to either place parentsat the beginning of the material script file, or to use the ’import’ directive (See Section 3.1.14[Script Import Directive], page 105). Note that inheritence is actually a copy - after scriptsare loaded into Ogre, objects no longer maintain their copy inheritance structure. If aparent material is modified through code at runtime, the changes have no effect on childmaterials that were copied from it in the script.


Material copying within the script alleviates some drudgery from copy/paste but havingthe ability to identify specific techniques, passes, and texture units to modify makes materialcopying easier. Techniques, passes, texture units can be identified directly in the childmaterial without having to layout previous techniques, passes, texture units by associating aname with them, Techniques and passes can take a name and texture units can be numberedwithin the material script. You can also use variables, See Section 3.1.13 [Script Variables],page 104.

Names become very useful in materials that copy from other materials. In order tooverride values they must be in the correct technique, pass, texture unit etc. The scriptcould be lain out using the sequence of techniques, passes, texture units in the child materialbut if only one parameter needs to change in say the 5th pass then the first four passesprior to the fifth would have to be placed in the script:

Here is an example:material test2 : test1{technique{

pass{}

pass{}

pass{}

pass{}

pass{

ambient 0.5 0.7 0.3 1.0}

}}

This method is tedious for materials that only have slight variations to their parent. Aneasier way is to name the pass directly without listing the previous passes:


material test2 : test1{technique 0{

pass 4{

ambient 0.5 0.7 0.3 1.0}

}}

The parent pass name must be known and the pass must be in the correct technique inorder for this to work correctly. Specifying the technique name and the pass name is thebest method. If the parent technique/pass are not named then use their index values fortheir name as done in the example.

Adding new Techniques, Passes, to copied materials:

If a new technique or pass needs to be added to a copied material then use a unique namefor the technique or pass that does not exist in the parent material. Using an index for thename that is one greater than the last index in the parent will do the same thing. The newtechnique/pass will be added to the end of the techniques/passes copied from the parentmaterial.

Note: if passes or techniques aren’t given a name, they will take on a default name basedon their index. For example the first pass has index 0 so its name will be 0.

Identifying Texture Units to override values

A specific texture unit state (TUS) can be given a unique name within a pass of a materialso that it can be identified later in cloned materials that need to override specified textureunit states in the pass without declaring previous texture units. Using a unique name fora Texture unit in a pass of a cloned material adds a new texture unit at the end of thetexture unit list for the pass.

material BumpMap2 : BumpMap1{technique ati8500{

pass 0{texture_unit NormalMap{

texture BumpyMetalNM.png}


}}

}

Advanced Script Inheritence

Starting with Ogre 1.6, script objects can now inherit from each other more generally.The previous concept of inheritance, material copying, was restricted only to the top-levelmaterial objects. Now, any level of object can take advantage of inheritance (for instance,techniques, passes, and compositor targets).

material Test{

technique{

pass : ParentPass{}

}}

Notice that the pass inherits from ParentPass. This allows for the creation of morefine-grained inheritance hierarchies.

Along with the more generalized inheritance system comes an important new keyword:"abstract." This keyword is used at a top-level object declaration (not inside any otherobject) to denote that it is not something that the compiler should actually attempt tocompile, but rather that it is only for the purpose of inheritance. For example, a materialdeclared with the abstract keyword will never be turned into an actual usable material inthe material framework. Objects which cannot be at a top-level in the document (like apass) but that you would like to declare as such for inheriting purpose must be declaredwith the abstract keyword.

abstract pass ParentPass{

diffuse 1 0 0 1}

That declares the ParentPass object which was inherited from in the above example.Notice the abstract keyword which informs the compiler that it should not attempt toactually turn this object into any sort of Ogre resource. If it did attempt to do so, then itwould obviously fail, since a pass all on its own like that is not valid.

The final matching option is based on wildcards. Using the ’*’ character, you can makea powerful matching scheme and override multiple objects at once, even if you don’t know


exact names or positions of those objects in the inherited object.

abstract technique Overrider{

pass *color*{

diffuse 0 0 0 0}

}

This technique, when included in a material, will override all passes matching the wild-card "*color*" (color has to appear in the name somewhere) and turn their diffuse propertiesblack. It does not matter their position or exact name in the inherited technique, this willmatch them.

3.1.12 Texture Aliases

Texture aliases are useful for when only the textures used in texture units need to be specifiedfor a cloned material. In the source material i.e. the original material to be cloned, eachtexture unit can be given a texture alias name. The cloned material in the script can thenspecify what textures should be used for each texture alias. Note that texture aliases area more specific version of Section 3.1.13 [Script Variables], page 104 which can be used toeasily set other values.

Using texture aliases within texture units:Format:texture alias <name>

Default: <name> will default to texture unit <name> if settexture_unit DiffuseTex{texture diffuse.jpg

}

texture alias defaults to DiffuseTex.

Example: The base material to be cloned:

material TSNormalSpecMapping{technique GLSL{

pass


{ambient 0.1 0.1 0.1diffuse 0.7 0.7 0.7specular 0.7 0.7 0.7 128

vertex_program_ref GLSLDemo/OffsetMappingVS{param_named_auto lightPosition light_position_object_space 0param_named_auto eyePosition camera_position_object_spaceparam_named textureScale float 1.0

}

fragment_program_ref GLSLDemo/TSNormalSpecMappingFS{

param_named normalMap int 0param_named diffuseMap int 1param_named fxMap int 2

}

// Normal maptexture_unit NormalMap{

texture defaultNM.pngtex_coord_set 0filtering trilinear

}

// Base diffuse texture maptexture_unit DiffuseMap{

texture defaultDiff.pngfiltering trilineartex_coord_set 1

}

// spec map for shininesstexture_unit SpecMap{

texture defaultSpec.pngfiltering trilineartex_coord_set 2

}

}

}


technique HLSL_DX9{

pass{

vertex_program_ref FxMap_HLSL_VS{

param_named_auto worldViewProj_matrix worldviewproj_matrixparam_named_auto lightPosition light_position_object_space 0param_named_auto eyePosition camera_position_object_space

}

fragment_program_ref FxMap_HLSL_PS{

param_named ambientColor float4 0.2 0.2 0.2 0.2}

// Normal maptexture_unit{

texture_alias NormalMaptexture defaultNM.pngtex_coord_set 0filtering trilinear

}

// Base diffuse texture maptexture_unit{

texture_alias DiffuseMaptexture defaultDiff.pngfiltering trilineartex_coord_set 1

}

// spec map for shininesstexture_unit{

texture_alias SpecMaptexture defaultSpec.pngfiltering trilineartex_coord_set 2

}

}

}


}

Note that the GLSL and HLSL techniques use the same textures. For each texture usagetype a texture alias is given that describes what the texture is used for. So the first textureunit in the GLSL technique has the same alias as the TUS in the HLSL technique since itsthe same texture used. Same goes for the second and third texture units.For demonstration purposes, the GLSL technique makes use of texture unit naming andtherefore the texture alias name does not have to be set since it defaults to the texture unitname. So why not use the default all the time since its less typing? For most situations youcan. Its when you clone a material that and then want to change the alias that you mustuse the texture alias command in the script. You cannot change the name of a texture unitin a cloned material so texture alias provides a facility to assign an alias name.

Now we want to clone the material but only want to change the textures used. We couldcopy and paste the whole material but if we decide to change the base material later thenwe also have to update the copied material in the script. With set texture alias, copying amaterial is very easy now. set texture alias is specified at the top of the material definition.All techniques using the specified texture alias will be effected by set texture alias.

Format:set texture alias <alias name> <texture name>

material fxTest : TSNormalSpecMapping{set_texture_alias NormalMap fxTestNMap.pngset_texture_alias DiffuseMap fxTestDiff.pngset_texture_alias SpecMap fxTestMap.png

}

The textures in both techniques in the child material will automatically get replacedwith the new ones we want to use.

The same process can be done in code as long you set up the texture alias namesso then there is no need to traverse technique/pass/TUS to change a texture. You justcall myMaterialPtr->applyTextureAliases(myAliasTextureNameList) which will update alltextures in all texture units that match the alias names in the map container reference youpassed as a parameter.

You don’t have to supply all the textures in the copied material.

material fxTest2 : fxTest{set_texture_alias DiffuseMap fxTest2Diff.png


set_texture_alias SpecMap fxTest2Map.png}

Material fxTest2 only changes the diffuse and spec maps of material fxTest and uses thesame normal map.

Another example:

material fxTest3 : TSNormalSpecMapping{set_texture_alias DiffuseMap fxTest2Diff.png

}

fxTest3 will end up with the default textures for the normal map and spec map setupin TSNormalSpecMapping material but will have a different diffuse map. So your basematerial can define the default textures to use and then the child materials can overridespecific textures.

3.1.13 Script Variables

A very powerful new feature in Ogre 1.6 is variables. Variables allow you to parameterizedata in materials so that they can become more generalized. This enables greater reuse ofscripts by targeting specific customization points. Using variables along with inheritanceallows for huge amounts of overrides and easy object reuse.

abstract pass ParentPass{

diffuse $diffuse_colour}

material Test{

technique{

pass : ParentPass{

set $diffuse_colour "1 0 0 1"}

}}

The ParentPass object declares a variable called "diffuse colour" which is then overrid-den in the Test material’s pass. The "set" keyword is used to set the value of that variable.The variable assignment follows lexical scoping rules, which means that the value of "1 0 01" is only valid inside that pass definition. Variable assignment in outer scopes carry overinto inner scopes.


material Test{

set $diffuse_colour "1 0 0 1"technique{

pass : ParentPass{}

}}

The $diffuse colour assignment carries down through the technique and into the pass.

3.1.14 Script Import Directive

Imports are a feature introduced to remove ambiguity from script dependencies. Whenusing scripts that inherit from each other but which are defined in separate files sometimeserrors occur because the scripts are loaded in incorrect order. Using imports removes thisissue. The script which is inheriting another can explicitly import its parent’s definitionwhich will ensure that no errors occur because the parent’s definition was not found.

import * from "parent.material"material Child : Parent{}

The material "Parent" is defined in parent.material and the import ensures that thosedefinitions are found properly. You can also import specific targets from within a file.

import Parent from "parent.material"

If there were other definitions in the parent.material file, they would not be imported.

Note, however that importing does not actually cause objects in the imported script tobe fully parsed & created, it just makes the definitions available for inheritence. This has aspecific ramification for vertex / fragment program definitions, which must be loaded beforeany parameters can be specified. You should continue to put common program definitionsin .program files to ensure they are fully parsed before being referenced in multiple .ma-terial files. The ’import’ command just makes sure you can resolve dependencies betweenequivalent script definitions (e.g. material to material).


3.2 Compositor Scripts

The compositor framework is a subsection of the OGRE API that allows you to easilydefine full screen post-processing effects. Compositor scripts offer you the ability to definecompositor effects in a script which can be reused and modified easily, rather than having touse the API to define them. You still need to use code to instantiate a compositor againstone of your visible viewports, but this is a much simpler process than actually defining thecompositor itself.

Compositor Fundamentals

Performing post-processing effects generally involves first rendering the scene to a texture,either in addition to or instead of the main window. Once the scene is in a texture, youcan then pull the scene image into a fragment program and perform operations on it byrendering it through full screen quad. The target of this post processing render can be themain result (e.g. a window), or it can be another render texture so that you can performmulti-stage convolutions on the image. You can even ’ping-pong’ the render back and forthbetween a couple of render textures to perform convolutions which require many iterations,without using a separate texture for each stage. Eventually you’ll want to render the resultto the final output, which you do with a full screen quad. This might replace the wholewindow (thus the main window doesn’t need to render the scene itself), or it might be acombinational effect.

So that we can discuss how to implement these techniques efficiently, a number of defi-nitions are required:

CompositorDefinition of a fullscreen effect that can be applied to a user viewport. This iswhat you’re defining when writing compositor scripts as detailed in this section.

Compositor InstanceAn instance of a compositor as applied to a single viewport. You create thesebased on compositor definitions, See Section 3.2.4 [Applying a Compositor],page 120.

Compositor ChainIt is possible to enable more than one compositor instance on a viewport at thesame time, with one compositor taking the results of the previous one as input.This is known as a compositor chain. Every viewport which has at least onecompositor attached to it has a compositor chain. See Section 3.2.4 [Applyinga Compositor], page 120

Target This is a RenderTarget, i.e. the place where the result of a series of renderoperations is sent. A target may be the final output (and this is implicit, youdon’t have to declare it), or it may be an intermediate render texture, whichyou declare in your script with the [compositor texture], page 109. A target


which is not the output target has a defined size and pixel format which youcan control.

Output TargetAs Target, but this is the single final result of all operations. The size and pixelformat of this target cannot be controlled by the compositor since it is definedby the application using it, thus you don’t declare it in your script. However,you do declare a Target Pass for it, see below.

Target PassA Target may be rendered to many times in the course of a composition effect.In particular if you ’ping pong’ a convolution between a couple of textures, youwill have more than one Target Pass per Target. Target passes are declared inthe script using a Section 3.2.2 [Compositor Target Passes], page 112, the latterbeing the final output target pass, of which there can be only one.

Pass Within a Target Pass, there are one or more individual Section 3.2.3 [Compos-itor Passes], page 114, which perform a very specific action, such as renderingthe original scene (or pulling the result from the previous compositor in thechain), rendering a fullscreen quad, or clearing one or more buffers. Typicallywithin a single target pass you will use the either a ’render scene’ pass or a’render quad’ pass, not both. Clear can be used with either type.

Loading scripts

Compositor scripts are loaded when resource groups are initialised: OGRE looks in allresource locations associated with the group (see Root::addResourceLocation) for files withthe ’.compositor’ extension and parses them. If you want to parse files manually, useCompositorSerializer::parseScript.

Format

Several compositors may be defined in a single script. The script format is pseudo-C++,with sections delimited by curly braces (’’, ’’), and comments indicated by starting a linewith ’//’ (note, no nested form comments allowed). The general format is shown below inthe example below:

// This is a comment// Black and white effectcompositor B&W{

technique{

// Temporary texturestexture rt0 target_width target_height PF_A8R8G8B8


target rt0{

// Render output from previous compositor (or original scene)input previous

}

target_output{

// Start with clear outputinput none// Draw a fullscreen quad with the black and white imagepass render_quad{

// Renders a fullscreen quad with a materialmaterial Ogre/Compositor/BlackAndWhiteinput 0 rt0

}}

}}

Every compositor in the script must be given a name, which is the line ’compositor<name>’ before the first opening ’’. This name must be globally unique. It can include pathcharacters (as in the example) to logically divide up your compositors, and also to avoidduplicate names, but the engine does not treat the name as hierarchical, just as a string.Names can include spaces but must be surrounded by double quotes ie compositor "MyName".

The major components of a compositor are the Section 3.2.1 [Compositor Techniques],page 108, the Section 3.2.2 [Compositor Target Passes], page 112 and the Section 3.2.3[Compositor Passes], page 114, which are covered in detail in the following sections.

3.2.1 Techniques

A compositor technique is much like a Section 3.1.1 [Techniques], page 21 in that it describesone approach to achieving the effect you’re looking for. A compositor definition can havemore than one technique if you wish to provide some fallback should the hardware notsupport the technique you’d prefer to use. Techniques are evaluated for hardware supportbased on 2 things:

Material supportAll Section 3.2.3 [Compositor Passes], page 114 that render a fullscreen quaduse a material; for the technique to be supported, all of the materials refer-enced must have at least one supported material technique. If they don’t, thecompositor technique is marked as unsupported and won’t be used.


Texture format supportThis one is slightly more complicated. When you request a[compositor texture], page 109 in your technique, you request a pixelformat. Not all formats are natively supported by hardware, especially thefloating point formats. However, in this case the hardware will typicallydowngrade the texture format requested to one that the hardware doessupport - with compositor effects though, you might want to use a differentapproach if this is the case. So, when evaluating techniques, the compositorwill first look for native support for the exact pixel format you’ve asked for,and will skip onto the next technique if it is not supported, thus allowing youto define other techniques with simpler pixel formats which use a differentapproach. If it doesn’t find any techniques which are natively supported, ittries again, this time allowing the hardware to downgrade the texture formatand thus should find at least some support for what you’ve asked for.

As with material techniques, compositor techniques are evaluated in the order you definethem in the script, so techniques declared first are preferred over those declared later.

Format: technique

Techniques can have the following nested elements:

• [compositor texture], page 109

• [compositor texture ref], page 111

• [compositor scheme], page 111

• [compositor logic], page 111

• Section 3.2.2 [Compositor Target Passes], page 112

• Section 3.2.2 [Compositor Target Passes], page 112

texture

This declares a render texture for use in subsequent Section 3.2.2 [Compositor TargetPasses], page 112.

Format: texture <Name> <Width> <Height> <Pixel Format> [<MRT Pixel Format2>][<MRT Pixel FormatN>] [pooled] [gamma] [no fsaa] [<scope>]

Here is a description of the parameters:

Name A name to give the render texture, which must be unique within this compos-itor. This name is used to reference the texture in Section 3.2.2 [CompositorTarget Passes], page 112, when the texture is rendered to, and in Section 3.2.3[Compositor Passes], page 114, when the texture is used as input to a materialrendering a fullscreen quad.


Width, HeightThe dimensions of the render texture. You can either specify a fixed widthand height, or you can request that the texture is based on the physical di-mensions of the viewport to which the compositor is attached. The optionsfor the latter are ’target width’, ’target height’, ’target width scaled <factor>’and ’target height scaled <factor>’ - where ’factor’ is the amount by which youwish to multiply the size of the main target to derive the dimensions.

Pixel FormatThe pixel format of the render texture. This affects how much memory itwill take, what colour channels will be available, and what precision youwill have within those channels. The available options are PF A8R8G8B8,PF R8G8B8A8, PF R8G8B8, PF FLOAT16 RGBA, PF FLOAT16 RGB,PF FLOAT16 R, PF FLOAT32 RGBA, PF FLOAT32 RGB, andPF FLOAT32 R.

pooled If present, this directive makes this texture ’pooled’ among compositor in-stances, which can save some memory.

gamma If present, this directive means that sRGB gamma correction will be enabledon writes to this texture. You should remember to include the opposite sRGBconversion when you read this texture back in another material, such as a quad.This option will automatically enabled if you use a render scene pass on thistexture and the viewport on which the compositor is based has sRGB writesupport enabled.

no fsaa If present, this directive disables the use of anti-aliasing on this texture. FSAAis only used if this texture is subject to a render scene pass and FSAA wasenabled on the original viewport on which this compositor is based; this optionallows you to override it and disable the FSAA if you wish.

scope If present, this directive sets the scope for the texture for being accessed by othercompositors using the [compositor texture ref], page 111 directive. There arethree options : ’local scope’ (which is also the default) means that only thecompositor defining the texture can access it. ’chain scope’ means that thecompositors after this compositor in the chain can reference its textures, and’global scope’ means that the entire application can access the texture. Thisdirective also affects the creation of the textures (global textures are createdonce and thus can’t be used with the pooled directive, and can’t rely on viewportsize).

Example: texture rt0 512 512 PF R8G8B8A8Example: texture rt1 target width target height PF FLOAT32 RGB

You can in fact repeat this element if you wish. If you do so, that means that thisrender texture becomes a Multiple Render Target (MRT), when the GPU writes to multipletextures at once. It is imperative that if you use MRT that the shaders that render to itrender to ALL the targets. Not doing so can cause undefined results. It is also importantto note that although you can use different pixel formats for each target in a MRT, each


one should have the same total bit depth since most cards do not support independent bitdepths. If you try to use this feature on cards that do not support the number of MRTsyou’ve asked for, the technique will be skipped (so you ought to write a fallback technique).

Example : texture mrt output target width target height PF FLOAT16 RGBAPF FLOAT16 RGBA chain scope

texture ref

This declares a reference of a texture from another compositor to be used in this compositor.

Format: texture ref <Local Name> <Reference Compositor> <Reference Texture Name>

Here is a description of the parameters:

Local NameA name to give the referenced texture, which must be unique within this com-positor. This name is used to reference the texture in Section 3.2.2 [CompositorTarget Passes], page 112, when the texture is rendered to, and in Section 3.2.3[Compositor Passes], page 114, when the texture is used as input to a materialrendering a fullscreen quad.

Reference CompositorThe name of the compositor that we are referencing a texture from

Reference Texture NameThe name of the texture in the compositor that we are referencing

Make sure that the texture being referenced is scoped accordingly (either chain or globalscope) and placed accordingly during chain creation (if referencing a chain-scoped texture,the compositor must be present in the chain and placed before the compositor referencingit).

Example : texture ref GBuffer GBufferCompositor mrt output

scheme

This gives a compositor technique a scheme name, allowing you to manually switch be-tween different techniques for this compositor when instantiated on a viewport by callingCompositorInstance::setScheme.

Format: material scheme <Name>

compositor logic

This connects between a compositor and code that it requires in order to function correctly.When an instance of this compositor will be created, the compositor logic will be notifiedand will have the chance to prepare the compositor’s operation (for example, adding alistener).


Format: compositor logic <Name>Registration of compositor logics is done by name through CompositorMan-

ager::registerCompositorLogic.

3.2.2 Target Passes

A target pass is the action of rendering to a given target, either a render texture or the finaloutput. You can update the same render texture multiple times by adding more than onetarget pass to your compositor script - this is very useful for ’ping pong’ renders between acouple of render textures to perform complex convolutions that cannot be done in a singlerender, such as blurring.

There are two types of target pass, the sort that updates a render texture:

Format: target <Name>

... and the sort that defines the final output render:

Format: target output

The contents of both are identical, the only real difference is that you can only have asingle target output entry, whilst you can have many target entries. Here are the attributesyou can use in a ’target’ or ’target output’ section of a .compositor script:• [compositor target input], page 112• [only initial], page 113• [visibility mask], page 113• [compositor lod bias], page 113• [material scheme], page 114• [compositor shadows], page 113• Section 3.2.3 [Compositor Passes], page 114


input

Sets input mode of the target, which tells the target pass what is pulled in before any of itsown passes are rendered.

Format: input (none | previous)

Default: input none


none The target will have nothing as input, all the contents of the target must begenerated using its own passes. Note this does not mean the target will beempty, just no data will be pulled in. For it to truly be blank you’d need a’clear’ pass within this target.

previous The target will pull in the previous contents of the viewport. This will be eitherthe original scene if this is the first compositor in the chain, or it will be theoutput from the previous compositor in the chain if the viewport has multiplecompositors enabled.

only initial

If set to on, this target pass will only execute once initially after the effect has been enabled.This could be useful to perform once-off renders, after which the static contents are usedby the rest of the compositor.

Format: only initial (on | off)

Default: only initial off

visibility mask

Sets the visibility mask for any render scene passes performed in this target pass. Thisis a bitmask (although it must be specified as decimal, not hex) and maps to SceneMan-ager::setVisibilityMask. Format: visibility mask <mask>

Default: visibility mask 4294967295

lod bias

Set the scene LOD bias for any render scene passes performed in this target pass. Thedefault is 1.0, everything below that means lower quality, higher means higher quality.

Format: lod bias <lodbias>

Default: lod bias 1.0

shadows

Sets whether shadows should be rendered during any render scene pass performed in thistarget pass. The default is ’on’.

Format: shadows (on | off)

Default: shadows on


material scheme

If set, indicates the material scheme to use for any render scene pass. Useful for performingspecial-case rendering effects.

Format: material scheme <scheme name>

Default: None

3.2.3 Compositor Passes

A pass is a single rendering action to be performed in a target pass.

Format: ’pass’ (render quad | clear | stencil | render scene | render custom) [customname]

There are four types of pass:

clear This kind of pass sets the contents of one or more buffers in the target to afixed value. So this could clear the colour buffer to a fixed colour, set the depthbuffer to a certain set of contents, fill the stencil buffer with a value, or anycombination of the above.

stencil This kind of pass configures stencil operations for the subsequent passes. Itcan set the stencil compare function, operations and reference values for you toperform your own stencil effects.

render sceneThis kind of pass performs a regular rendering of the scene. It willuse the [visibility mask], page 113, [compositor lod bias], page 113, and[material scheme], page 114 from the parent target pass.

render quadThis kind of pass renders a quad over the entire render target, using a givenmaterial. You will undoubtedly want to pull in the results of other target passesinto this operation to perform fullscreen effects.

render customThis kind of pass is just a callback to user code for the compositionpass specified in the custom name (and registered via CompositorMan-ager::registerCustomCompositionPass) and allows the user to create customrender operations for more advanced effects. This is the only pass type thatrequires the custom name parameter.

Here are the attributes you can use in a ’pass’ section of a .compositor script:


Available Pass Attributes

• [material], page 115• [compositor pass input], page 115• [compositor pass identifier], page 115• [first render queue], page 116• [last render queue], page 116• [compositor pass material scheme], page 116• [compositor clear], page 116• [compositor stencil], page 117

material

For passes of type ’render quad’, sets the material used to render the quad. Youwill want to use shaders in this material to perform fullscreen effects, and use the[compositor pass input], page 115 attribute to map other texture targets into the texturebindings needed by this material.

Format: material <Name>

input

For passes of type ’render quad’, this is how you map one or more local render textures(See [compositor texture], page 109) into the material you’re using to render the fullscreenquad. To bind more than one texture, repeat this attribute with different sampler indexes.

Format: input <sampler> <Name> [<MRTIndex>]

sampler The texture sampler to set, must be a number in the range [0,OGRE MAX TEXTURE LAYERS-1].

Name The name of the local render texture to bind, as declared in[compositor texture], page 109 and rendered to in one or moreSection 3.2.2 [Compositor Target Passes], page 112.

MRTIndexIf the local texture that you’re referencing is a Multiple Render Target (MRT),this identifies the surface from the MRT that you wish to reference (0 is thefirst surface, 1 the second etc).

Example: input 0 rt0

identifier

Associates a numeric identifier with the pass. This is useful for registering a listener withthe compositor (CompositorInstance::addListener), and being able to identify which pass itis that’s being processed when you get events regarding it. Numbers between 0 and 2^32


are allowed.

Format: identifier <number>

Example: identifier 99945

Default: identifier 0

first render queue

For passes of type ’render scene’, this sets the first render queue id that is included in therender. Defaults to the value of RENDER QUEUE SKIES EARLY.

Format: first render queue <id>

Default: first render queue 0

last render queue

For passes of type ’render scene’, this sets the last render queue id that is included in therender. Defaults to the value of RENDER QUEUE SKIES LATE.

Format: last render queue <id>

Default: last render queue 95

material scheme

If set, indicates the material scheme to use for this pass only. Useful for performing special-case rendering effects.

This will overwrite the scheme if set at the target scope as well.

Format: material scheme <scheme name>

Default: None

Clear Section

For passes of type ’clear’, this section defines the buffer clearing parameters.

Format: clear


Here are the attributes you can use in a ’clear’ section of a .compositor script:• [compositor clear buffers], page 117• [compositor clear colour value], page 117• [compositor clear depth value], page 117• [compositor clear stencil value], page 117

buffers

Sets the buffers cleared by this pass.

Format: buffers [colour] [depth] [stencil]

Default: buffers colour depth

colour value

Set the colour used to fill the colour buffer by this pass, if the colour buffer is beingcleared ([compositor clear buffers], page 117).

Format: colour value <red> <green> <blue> <alpha>

Default: colour value 0 0 0 0

depth value

Set the depth value used to fill the depth buffer by this pass, if the depth buffer is beingcleared ([compositor clear buffers], page 117).

Format: depth value <depth>

Default: depth value 1.0

stencil value

Set the stencil value used to fill the stencil buffer by this pass, if the stencil buffer isbeing cleared ([compositor clear buffers], page 117).

Format: stencil value <value>

Default: stencil value 0.0


Stencil Section

For passes of type ’stencil’, this section defines the stencil operation parameters.

Format: stencil

Here are the attributes you can use in a ’stencil’ section of a .compositor script:

• [compositor stencil check], page 118

• [compositor stencil comp func], page 118

• [compositor stencil ref value], page 118

• [compositor stencil mask], page 119

• [compositor stencil fail op], page 119

• [compositor stencil depth fail op], page 119

• [compositor stencil pass op], page 120

• [compositor stencil two sided], page 120

check

Enables or disables the stencil check, thus enabling the use of the rest of the featuresin this section. The rest of the options in this section do nothing if the stencil check isoff. Format: check (on | off)

comp func

Sets the function used to perform the following comparison:

(ref value & mask) comp func (Stencil Buffer Value & mask)

What happens as a result of this comparison will be one of 3 actions on the stencilbuffer, depending on whether the test fails, succeeds but with the depth buffer checkstill failing, or succeeds with the depth buffer check passing too. You set the actionsin the [compositor stencil fail op], page 119, [compositor stencil depth fail op],page 119 and [compositor stencil pass op], page 120 respectively. If the stencil checkfails, no colour or depth are written to the frame buffer.

Format: comp func (always fail | always pass | less | less equal | not equal |greater equal | greater)

Default: comp func always pass


ref value

Sets the reference value used to compare with the stencil buffer as described in[compositor stencil comp func], page 118.

Format: ref value <value>

Default: ref value 0.0

mask

Sets the mask used to compare with the stencil buffer as described in[compositor stencil comp func], page 118.

Format: mask <value>

Default: mask 4294967295

fail op

Sets what to do with the stencil buffer value if the result of the stencil comparison([compositor stencil comp func], page 118) and depth comparison is that both fail.

Format: fail op (keep | zero | replace | increment | decrement | increment wrap |decrement wrap | invert)

Default: depth fail op keep

These actions mean:

keep Leave the stencil buffer unchanged.

zero Set the stencil value to zero.

replace Set the stencil value to the reference value.

increment Add one to the stencil value, clamping at the maximum value.

decrement Subtract one from the stencil value, clamping at 0.

increment wrapAdd one to the stencil value, wrapping back to 0 at the maximum.

decrement wrapSubtract one from the stencil value, wrapping to the maximum below 0.

invert invert the stencil value.

depth fail op

Sets what to do with the stencil buffer value if the result of the stencil comparison([compositor stencil comp func], page 118) passes but the depth comparison fails.


Format: depth fail op (keep | zero | replace | increment | decrement | increment wrap| decrement wrap | invert)

Default: depth fail op keep

pass op

Sets what to do with the stencil buffer value if the result of the stencil comparison([compositor stencil comp func], page 118) and the depth comparison pass.

Format: pass op (keep | zero | replace | increment | decrement | increment wrap |decrement wrap | invert)

Default: pass op keep

two sided

Enables or disables two-sided stencil operations, which means the inverse of the oper-ations applies to back-facing polygons.

Format: two sided (on | off)

Default: two sided off

3.2.4 Applying a Compositor

Adding a compositor instance to a viewport is very simple. All you need to do is:

CompositorManager::getSingleton().addCompositor(viewport, compositorName);

Where viewport is a pointer to your viewport, and compositorName is the name of thecompositor to create an instance of. By doing this, a new instance of a compositor willbe added to a new compositor chain on that viewport. You can call the method multipletimes to add further compositors to the chain on this viewport. By default, each compositorwhich is added is disabled, but you can change this state by calling:

CompositorManager::getSingleton().setCompositorEnabled(viewport, compositorName, enabledOrDisabled);


For more information on defining and using compositors, see Demo Compositor in theSamples area, together with the Examples.compositor script in the media area.

3.3 Particle Scripts

Particle scripts allow you to define particle systems to be instantiated in your code withouthaving to hard-code the settings themselves in your source code, allowing a very quickturnaround on any changes you make. Particle systems which are defined in scripts areused as templates, and multiple actual systems can be created from them at runtime.

Loading scripts

Particle system scripts are loaded at initialisation time by the system: by default it looks inall common resource locations (see Root::addResourceLocation) for files with the ’.particle’extension and parses them. If you want to parse files with a different extension, use the Par-ticleSystemManager::getSingleton().parseAllSources method with your own extension, or ifyou want to parse an individual file, use ParticleSystemManager::getSingleton().parseScript.

Once scripts have been parsed, your code is free to instantiate systems based on themusing the SceneManager::createParticleSystem() method which can take both a name forthe new system, and the name of the template to base it on (this template name is in thescript).

Format

Several particle systems may be defined in a single script. The script format is pseudo-C++,with sections delimited by curly braces (), and comments indicated by starting a line with’//’ (note, no nested form comments allowed). The general format is shown below in atypical example:// A sparkly purple fountainparticle_system Examples/PurpleFountain{

material Examples/Flare2particle_width 20particle_height 20cull_each falsequota 10000billboard_type oriented_self

// Area emitteremitter Point


{angle 15emission_rate 75time_to_live 3direction 0 1 0velocity_min 250velocity_max 300colour_range_start 1 0 0colour_range_end 0 0 1

}

// Gravityaffector LinearForce{

force_vector 0 -100 0force_application add

}

// Faderaffector ColourFader{

red -0.25green -0.25blue -0.25

}}

Every particle system in the script must be given a name, which is the line before thefirst opening ’’, in the example this is ’Examples/PurpleFountain’. This name must beglobally unique. It can include path characters (as in the example) to logically divide upyour particle systems, and also to avoid duplicate names, but the engine does not treat thename as hierarchical, just as a string.

A system can have top-level attributes set using the scripting commands available, suchas ’quota’ to set the maximum number of particles allowed in the system. Emitters (whichcreate particles) and affectors (which modify particles) are added as nested definitions withinthe script. The parameters available in the emitter and affector sections are entirely depen-dent on the type of emitter / affector.

For a detailed description of the core particle system attributes, see the list below:

Available Particle System Attributes

• [quota], page 123


• [particle material], page 123• [particle width], page 124• [particle height], page 124• [cull each], page 124• [billboard type], page 125• [billboard origin], page 126• [billboard rotation type], page 127• [common direction], page 127• [common up vector], page 128• [particle renderer], page 124• [particle sorted], page 125• [particle localspace], page 125• [particle point rendering], page 128• [particle accurate facing], page 129• [iteration interval], page 129• [nonvisible update timeout], page 129

See also: Section 3.3.2 [Particle Emitters], page 130, Section 3.3.5 [Particle Affectors],page 137

3.3.1 Particle System Attributes

This section describes to attributes which you can set on every particle system using scripts.All attributes have default values so all settings are optional in your script.

quota

Sets the maximum number of particles this system is allowed to contain at one time. Whenthis limit is exhausted, the emitters will not be allowed to emit any more particles untilsome destroyed (e.g. through their time to live running out). Note that you will almostalways want to change this, since it defaults to a very low value (particle pools are onlyever increased in size, never decreased).

format: quota <max particles>example: quota 10000default: 10

material

Sets the name of the material which all particles in this system will use. All particles in asystem use the same material, although each particle can tint this material through the useof it’s colour property.


format: material <material name>example: material Examples/Flaredefault: none (blank material)

particle width

Sets the width of particles in world coordinates. Note that this property is absolute whenbillboard type (see below) is set to ’point’ or ’perpendicular self’, but is scaled by thelength of the direction vector when billboard type is ’oriented common’, ’oriented self’ or’perpendicular common’.

format: particle width <width>example: particle width 20default: 100

particle height

Sets the height of particles in world coordinates. Note that this property is absolute whenbillboard type (see below) is set to ’point’ or ’perpendicular self’, but is scaled by thelength of the direction vector when billboard type is ’oriented common’, ’oriented self’ or’perpendicular common’.

format: particle height <height>example: particle height 20default: 100

cull each

All particle systems are culled by the bounding box which contains all the particles in thesystem. This is normally sufficient for fairly locally constrained particle systems wheremost particles are either visible or not visible together. However, for those that spreadparticles over a wider area (e.g. a rain system), you may want to actually cull each particleindividually to save on time, since it is far more likely that only a subset of the particleswill be visible. You do this by setting the cull each parameter to true.

format: cull each <true|false>example: cull each truedefault: false

renderer

Particle systems do not render themselves, they do it through ParticleRenderer classes.Those classes are registered with a manager in order to provide particle systems with a


particular ’look’. OGRE comes configured with a default billboard-based renderer, butmore can be added through plugins. Particle renders are registered with a unique name,and you can use that name in this attribute to determine the renderer to use. The defaultis ’billboard’.

Particle renderers can have attributes, which can be passed by setting them on the rootparticle system.

format: renderer <renderer name>default: billboard

sorted

By default, particles are not sorted. By setting this attribute to ’true’, the particles will besorted with respect to the camera, furthest first. This can make certain rendering effectslook better at a small sorting expense.

format: sorted <true|false>default: false

local space

By default, particles are emitted into world space, such that if you transform the node towhich the system is attached, it will not affect the particles (only the emitters). This tendsto give the normal expected behaviour, which is to model how real world particles travelindependently from the objects they are emitted from. However, to create some effects youmay want the particles to remain attached to the local space the emitter is in and to followthem directly. This option allows you to do that.

format: local space <true|false>default: false

billboard type

This is actually an attribute of the ’billboard’ particle renderer (the default), and is anexample of passing attributes to a particle renderer by declaring them directly within thesystem declaration. Particles using the default renderer are rendered using billboards, whichare rectangles formed by 2 triangles which rotate to face the given direction. However, thereis more than 1 way to orient a billboard. The classic approach is for the billboard to directlyface the camera: this is the default behaviour. However this arrangement only looks goodfor particles which are representing something vaguely spherical like a light flare. For morelinear effects like laser fire, you actually want the particle to have an orientation of it’s own.


format: billboard type <point|oriented common|oriented self|perpendicular common|perpendicular self>

example: billboard type oriented selfdefault: point

The options for this parameter are:

point The default arrangement, this approximates spherical particles and the bill-boards always fully face the camera.

oriented commonParticles are oriented around a common, typically fixed direction vector (see[common direction], page 127), which acts as their local Y axis. The billboardrotates only around this axis, giving the particle some sense of direction. Goodfor rainstorms, starfields etc where the particles will traveling in one direction- this is slightly faster than oriented self (see below).

oriented selfParticles are oriented around their own direction vector, which acts as theirlocal Y axis. As the particle changes direction, so the billboard reorients itselfto face this way. Good for laser fire, fireworks and other ’streaky’ particles thatshould look like they are traveling in their own direction.

perpendicular commonParticles are perpendicular to a common, typically fixed direction vector (see[common direction], page 127), which acts as their local Z axis, and their lo-cal Y axis coplanar with common direction and the common up vector (see[common up vector], page 128). The billboard never rotates to face the cam-era, you might use double-side material to ensure particles never culled byback-facing. Good for aureolas, rings etc where the particles will perpendicularto the ground - this is slightly faster than perpendicular self (see below).

perpendicular selfParticles are perpendicular to their own direction vector, which acts as theirlocal Z axis, and their local Y axis coplanar with their own direction vectorand the common up vector (see [common up vector], page 128). The billboardnever rotates to face the camera, you might use double-side material to en-sure particles never culled by back-facing. Good for rings stack etc where theparticles will perpendicular to their traveling direction.

billboard origin

Specifying the point which acts as the origin point for all billboard particles, controls thefine tuning of where a billboard particle appears in relation to it’s position.

format: billboard origin <top left|top center|top right|center left|center|center right|bottom left|bottom center|bottom right>


example: billboard origin top rightdefault: center


top left The billboard origin is the top-left corner.

top center The billboard origin is the center of top edge.

top right The billboard origin is the top-right corner.

center left The billboard origin is the center of left edge.

center The billboard origin is the center.

center rightThe billboard origin is the center of right edge.

bottom leftThe billboard origin is the bottom-left corner.

bottom centerThe billboard origin is the center of bottom edge.

bottom rightThe billboard origin is the bottom-right corner.

billboard rotation type

By default, billboard particles will rotate the texture coordinates to according with particlerotation. But rotate texture coordinates has some disadvantage, e.g. the corners of thetexture will lost after rotate, and the corners of the billboard will fill with unwanted texturearea when using wrap address mode or sub-texture sampling. This settings allow youspecifying other rotation type.

format: billboard rotation type <vertex|texcoord>example: billboard rotation type vertexdefault: texcoord


vertex Billboard particles will rotate the vertices around their facing direction to ac-cording with particle rotation. Rotate vertices guarantee texture corners exactlymatch billboard corners, thus has advantage mentioned above, but should takemore time to generate the vertices.

texcoord Billboard particles will rotate the texture coordinates to according with particlerotation. Rotate texture coordinates is faster than rotate vertices, but has somedisadvantage mentioned above.


common direction

Only required if [billboard type], page 125 is set to oriented common or perpendicu-lar common, this vector is the common direction vector used to orient all particles in thesystem.

format: common direction <x> <y> <z>example: common direction 0 -1 0default: 0 0 1


common up vector

Only required if [billboard type], page 125 is set to perpendicular self or perpendicu-lar common, this vector is the common up vector used to orient all particles in the system.

format: common up vector <x> <y> <z>example: common up vector 0 1 0default: 0 1 0


point rendering

This is actually an attribute of the ’billboard’ particle renderer (the default), and setswhether or not the BillboardSet will use point rendering rather than manually generatedquads.

By default a BillboardSet is rendered by generating geometry for a textured quad inmemory, taking into account the size and orientation settings, and uploading it to thevideo card. The alternative is to use hardware point rendering, which means that only oneposition needs to be sent per billboard rather than 4 and the hardware sorts out how thisis rendered based on the render state.

Using point rendering is faster than generating quads manually, but is more restrictive.The following restrictions apply:• Only the ’point’ orientation type is supported• Size and appearance of each particle is controlled by the material pass ([point size],

page 44, [point size attenuation], page 45, [point sprites], page 44)


• Per-particle size is not supported (stems from the above)

• Per-particle rotation is not supported, and this can only be controlled through textureunit rotation in the material definition

• Only ’center’ origin is supported

• Some drivers have an upper limit on the size of points they support - this can evenvary between APIs on the same card! Don’t rely on point sizes that cause the pointsprites to get very large on screen, since they may get clamped on some cards. Uppersizes can range from 64 to 256 pixels.

You will almost certainly want to enable in your material pass both point attenuationand point sprites if you use this option.

accurate facing

This is actually an attribute of the ’billboard’ particle renderer (the default), and setswhether or not the BillboardSet will use a slower but more accurate calculation for facingthe billboard to the camera. Bt default it uses the camera direction, which is faster butmeans the billboards don’t stay in the same orientation as you rotate the camera. The’accurate facing true’ option makes the calculation based on a vector from each billboardto the camera, which means the orientation is constant even whilst the camera rotates.

format: accurate facing on|offdefault: accurate facing off 0

iteration interval

Usually particle systems are updated based on the frame rate; however this can give variableresults with more extreme frame rate ranges, particularly at lower frame rates. You can usethis option to make the update frequency a fixed interval, whereby at lower frame rates,the particle update will be repeated at the fixed interval until the frame time is used up. Avalue of 0 means the default frame time iteration.

format: iteration interval <secs>example: iteration interval 0.01default: iteration interval 0


nonvisible update timeout

Sets when the particle system should stop updating after it hasn’t been visible for a while.By default, visible particle systems update all the time, even when not in view. This meansthat they are guaranteed to be consistent when they do enter view. However, this comes ata cost, updating particle systems can be expensive, especially if they are perpetual.

This option lets you set a ’timeout’ on the particle system, so that if it isn’t visible forthis amount of time, it will stop updating until it is next visible. A value of 0 disables thetimeout and always updates.

format: nonvisible update timeout <secs>example: nonvisible update timeout 10default: nonvisible update timeout 0

3.3.2 Particle Emitters

Particle emitters are classified by ’type’ e.g. ’Point’ emitters emit from a single pointwhilst ’Box’ emitters emit randomly from an area. New emitters can be added to Ogreby creating plugins. You add an emitter to a system by nesting another section withinit, headed with the keyword ’emitter’ followed by the name of the type of emitter (casesensitive). Ogre currently supports ’Point’, ’Box’, ’Cylinder’, ’Ellipsoid’, ’HollowEllipsoid’and ’Ring’ emitters.

It is also possible to ’emit emitters’ - that is, have new emitters spawned based on theposition of particles. See [Emitting Emitters], page 137

Particle Emitter Universal Attributes

• [angle], page 131• [colour], page 131• [colour range start], page 131• [colour range end], page 131• [direction], page 132• [emission rate], page 132• [position], page 132• [velocity], page 132• [velocity min], page 133• [velocity max], page 133• [time to live], page 133• [time to live min], page 133


• [time to live max], page 133• [duration], page 133• [duration min], page 134• [duration max], page 134• [repeat delay], page 134• [repeat delay min], page 134• [repeat delay max], page 134

See also: Section 3.3 [Particle Scripts], page 121, Section 3.3.5 [Particle Affectors], page 137

3.3.3 Particle Emitter Attributes

This section describes the common attributes of all particle emitters. Specific emitter typesmay also support their own extra attributes.

angle

Sets the maximum angle (in degrees) which emitted particles may deviate from the directionof the emitter (see direction). Setting this to 10 allows particles to deviate up to 10 degreesin any direction away from the emitter’s direction. A value of 180 means emit in anydirection, whilst 0 means emit always exactly in the direction of the emitter.

format: angle <degrees>example: angle 30default: 0

colour

Sets a static colour for all particle emitted. Also see the colour range start andcolour range end attributes for setting a range of colours. The format of the colourparameter is "r g b a", where each component is a value from 0 to 1, and the alpha valueis optional (assumes 1 if not specified).

format: colour <r> <g> <b> [<a>]example: colour 1 0 0 1default: 1 1 1 1

colour range start & colour range end

As the ’colour’ attribute, except these 2 attributes must be specified together, and indicatethe range of colours available to emitted particles. The actual colour will be randomly


chosen between these 2 values.

format: as colourexample (generates random colours between red and blue):

colour range start 1 0 0colour range end 0 0 1

default: both 1 1 1 1

direction

Sets the direction of the emitter. This is relative to the SceneNode which the particle systemis attached to, meaning that as with other movable objects changing the orientation of thenode will also move the emitter.

format: direction <x> <y> <z>example: direction 0 1 0default: 1 0 0

emission rate

Sets how many particles per second should be emitted. The specific emitter does not haveto emit these in a continuous burst - this is a relative parameter and the emitter may chooseto emit all of the second’s worth of particles every half-second for example, the behaviourdepends on the emitter. The emission rate will also be limited by the particle system’s’quota’ setting.

format: emission rate <particles per second>example: emission rate 50default: 10

position

Sets the position of the emitter relative to the SceneNode the particle system is attachedto.

format: position <x> <y> <z>example: position 10 0 40default: 0 0 0


velocity

Sets a constant velocity for all particles at emission time. See also the velocity min andvelocity max attributes which allow you to set a range of velocities instead of a fixed one.

format: velocity <world units per second>example: velocity 100default: 1

velocity min & velocity max

As ’velocity’ except these attributes set a velocity range and each particle is emitted witha random velocity within this range.

format: as velocityexample:

velocity min 50velocity max 100

default: both 1

time to live

Sets the number of seconds each particle will ’live’ for before being destroyed. NB it ispossible for particle affectors to alter this in flight, but this is the value given to particleson emission. See also the time to live min and time to live max attributes which let youset a lifetime range instead of a fixed one.

format: time to live <seconds>example: time to live 10default: 5

time to live min & time to live max

As time to live, except this sets a range of lifetimes and each particle gets a random valuein-between on emission.

format: as time to liveexample:

time to live min 2time to live max 5

default: both 5


duration

Sets the number of seconds the emitter is active. The emitter can be started again, see[repeat delay], page 134. A value of 0 means infinite duration. See also the duration minand duration max attributes which let you set a duration range instead of a fixed one.

format: duration <seconds>example:

duration 2.5default: 0

duration min & duration max

As duration, except these attributes set a variable time range between the min and maxvalues each time the emitter is started.

format: as durationexample:

duration min 2duration max 5

default: both 0

repeat delay

Sets the number of seconds to wait before the emission is repeated when stopped by a limited[duration], page 133. See also the repeat delay min and repeat delay max attributes whichallow you to set a range of repeat delays instead of a fixed one.

format: repeat delay <seconds>example:

repeat delay 2.5default: 0

repeat delay min & repeat delay max

As repeat delay, except this sets a range of repeat delays and each time the emitter isstarted it gets a random value in-between.

format: as repeat delayexample:


repeat delay 2repeat delay 5

default: both 0

See also: Section 3.3.4 [Standard Particle Emitters], page 135, Section 3.3 [ParticleScripts], page 121, Section 3.3.5 [Particle Affectors], page 137

3.3.4 Standard Particle Emitters

Ogre comes preconfigured with a few particle emitters. New ones can be added by creatingplugins: see the Plugin ParticleFX project as an example of how you would do this (this iswhere these emitters are implemented).• [Point Emitter], page 135• [Box Emitter], page 135• [Cylinder Emitter], page 136• [Ellipsoid Emitter], page 136• [Hollow Ellipsoid Emitter], page 136• [Ring Emitter], page 137

Point Emitter

This emitter emits particles from a single point, which is it’s position. This emitter has noadditional attributes over an above the standard emitter attributes.

To create a point emitter, include a section like this within your particle system script:

emitter Point{

// Settings go here}

Please note that the name of the emitter (’Point’) is case-sensitive.

Box Emitter

This emitter emits particles from a random location within a 3-dimensional box. It’s extraattributes are:

width Sets the width of the box (this is the size of the box along it’s local X axis,which is dependent on the ’direction’ attribute which forms the box’s local Z).


format: width <units>example: width 250default: 100

height Sets the height of the box (this is the size of the box along it’s local Y axis,which is dependent on the ’direction’ attribute which forms the box’s local Z).format: height <units>example: height 250default: 100

depth Sets the depth of the box (this is the size of the box along it’s local Z axis,which is the same as the ’direction’ attribute).format: depth <units>example: depth 250default: 100

To create a box emitter, include a section like this within your particle system script:

emitter Box{


Cylinder Emitter

This emitter emits particles in a random direction from within a cylinder area, where thecylinder is oriented along the Z-axis. This emitter has exactly the same parameters as the[Box Emitter], page 135 so there are no additional parameters to consider here - the widthand height determine the shape of the cylinder along it’s axis (if they are different it is anellipsoid cylinder), the depth determines the length of the cylinder.

Ellipsoid Emitter

This emitter emits particles from within an ellipsoid shaped area, i.e. a sphere or squashed-sphere area. The parameters are again identical to the [Box Emitter], page 135, except thatthe dimensions describe the widest points along each of the axes.

Hollow Ellipsoid Emitter

This emitter is just like [Ellipsoid Emitter], page 136 except that there is a hollow area inthe centre of the ellipsoid from which no particles are emitted. Therefore it has 3 extraparameters in order to define this area:

inner widthThe width of the inner area which does not emit any particles.

inner heightThe height of the inner area which does not emit any particles.


inner depthThe depth of the inner area which does not emit any particles.

Ring Emitter

This emitter emits particles from a ring-shaped area, i.e. a little like [Hollow EllipsoidEmitter], page 136 except only in 2 dimensions.

inner widthThe width of the inner area which does not emit any particles.

inner heightThe height of the inner area which does not emit any particles.

See also: Section 3.3 [Particle Scripts], page 121, Section 3.3.2 [Particle Emitters],page 130

Emitting Emitters

It is possible to spawn new emitters on the expiry of particles, for example to product’firework’ style effects. This is controlled via the following directives:

emit emitter quotaThis parameter is a system-level parameter telling the system how many emittedemitters may be in use at any one time. This is just to allow for the spaceallocation process.

name This parameter is an emitter-level parameter, giving a name to an emitter. Thiscan then be referred to in another emitter as the new emitter type to spawnwhen an emitted particle dies.

emit emitterThis is an emitter-level parameter, and if specified, it means that when particlesemitted by this emitter die, they spawn a new emitter of the named type.

3.3.5 Particle Affectors

Particle affectors modify particles over their lifetime. They are classified by ’type’ e.g.’LinearForce’ affectors apply a force to all particles, whilst ’ColourFader’ affectors alter thecolour of particles in flight. New affectors can be added to Ogre by creating plugins. Youadd an affector to a system by nesting another section within it, headed with the keyword’affector’ followed by the name of the type of affector (case sensitive). Ogre currentlysupports ’LinearForce’ and ’ColourFader’ affectors.

Particle affectors actually have no universal attributes; they are all specific to the typeof affector.


See also: Section 3.3.6 [Standard Particle Affectors], page 138, Section 3.3 [ParticleScripts], page 121, Section 3.3.2 [Particle Emitters], page 130

3.3.6 Standard Particle Affectors

Ogre comes preconfigured with a few particle affectors. New ones can be added by creatingplugins: see the Plugin ParticleFX project as an example of how you would do this (this iswhere these affectors are implemented).• [Linear Force Affector], page 138• [ColourFader Affector], page 139• [ColourFader2 Affector], page 139• [Scaler Affector], page 141• [Rotator Affector], page 141• [ColourInterpolator Affector], page 142• [ColourImage Affector], page 143• [DeflectorPlane Affector], page 143• [DirectionRandomiser Affector], page 144

Linear Force Affector

This affector applies a force vector to all particles to modify their trajectory. Can be usedfor gravity, wind, or any other linear force. It’s extra attributes are:

force vectorSets the vector for the force to be applied to every particle. The magnitude ofthis vector determines how strong the force is.

format: force vector <x> <y> <z>example: force vector 50 0 -50default: 0 -100 0 (a fair gravity effect)

force applicationSets the way in which the force vector is applied to particle momentum.

format: force application <add|average>example: force application averagedefault: add

The options are:

average The resulting momentum is the average of the force vector and theparticle’s current motion. Is self-stabilising but the speed at whichthe particle changes direction is non-linear.

add The resulting momentum is the particle’s current motion plus theforce vector. This is traditional force acceleration but can poten-tially result in unlimited velocity.

To create a linear force affector, include a section like this within your particle system script:


affector LinearForce{


Please note that the name of the affector type (’LinearForce’) is case-sensitive.

ColourFader Affector

This affector modifies the colour of particles in flight. It’s extra attributes are:

red Sets the adjustment to be made to the red component of the particle colour persecond.

format: red <delta value>example: red -0.1default: 0

green Sets the adjustment to be made to the green component of the particle colourper second.

format: green <delta value>example: green -0.1default: 0

blue Sets the adjustment to be made to the blue component of the particle colourper second.

format: blue <delta value>example: blue -0.1default: 0

alpha Sets the adjustment to be made to the alpha component of the particle colourper second.

format: alpha <delta value>example: alpha -0.1default: 0

To create a colour fader affector, include a section like this within your particle systemscript:

affector ColourFader{


ColourFader2 Affector

This affector is similar to the [ColourFader Affector], page 139, except it introduces twostates of colour changes as opposed to just one. The second colour change state is activatedonce a specified amount of time remains in the particles life.


red1 Sets the adjustment to be made to the red component of the particle colour persecond for the first state.


green1 Sets the adjustment to be made to the green component of the particle colourper second for the first state.


blue1 Sets the adjustment to be made to the blue component of the particle colourper second for the first state.


alpha1 Sets the adjustment to be made to the alpha component of the particle colourper second for the first state.


red2 Sets the adjustment to be made to the red component of the particle colour persecond for the second state.


green2 Sets the adjustment to be made to the green component of the particle colourper second for the second state.


blue2 Sets the adjustment to be made to the blue component of the particle colourper second for the second state.


alpha2 Sets the adjustment to be made to the alpha component of the particle colourper second for the second state.



state changeWhen a particle has this much time left to live, it will switch to state 2.

format: state change <seconds>example: state change 2default: 1

To create a ColourFader2 affector, include a section like this within your particle systemscript:

affector ColourFader2{


Scaler Affector

This affector scales particles in flight. It’s extra attributes are:

rate The amount by which to scale the particles in both the x and y direction persecond.

To create a scale affector, include a section like this within your particle system script:

affector Scaler{


Rotator Affector

This affector rotates particles in flight. This is done by rotating the texture. It’s extraattributes are:

rotation speed range startThe start of a range of rotation speeds to be assigned to emitted particles.

format: rotation speed range start <degrees per second>example: rotation speed range start 90default: 0

rotation speed range endThe end of a range of rotation speeds to be assigned to emitted particles.

format: rotation speed range end <degrees per second>example: rotation speed range end 180default: 0


rotation range startThe start of a range of rotation angles to be assigned to emitted particles.

format: rotation range start <degrees>example: rotation range start 0default: 0

rotation range endThe end of a range of rotation angles to be assigned to emitted particles.

format: rotation range end <degrees>example: rotation range end 360default: 0

To create a rotate affector, include a section like this within your particle system script:

affector Rotator{


ColourInterpolator Affector

Similar to the ColourFader and ColourFader2 Affector?s, this affector modifies the colourof particles in flight, except it has a variable number of defined stages. It swaps the particlecolour for several stages in the life of a particle and interpolates between them. It’s extraattributes are:

time0 The point in time of stage 0.format: time0 <0-1 based on lifetime>

example: time0 0default: 1

colour0 The colour at stage 0.format: colour0 <r> <g> <b> [<a>]

example: colour0 1 0 0 1default: 0.5 0.5 0.5 0.0


example: time1 0.5default: 1





example: time2 1default: 1



[...]

The number of stages is variable. The maximal number of stages is 6; where time5 andcolour5 are the last possible parameters. To create a colour interpolation affector, includea section like this within your particle system script:

affector ColourInterpolator{


ColourImage Affector

This is another affector that modifies the colour of particles in flight, but instead of pro-grammatically defining colours, the colours are taken from a specified image file. The rangeof colour values begins from the left side of the image and move to the right over the life-time of the particle, therefore only the horizontal dimension of the image is used. Its extraattributes are:

image The start of a range of rotation speed to be assigned to emitted particles.format: image <image name>

example: image rainbow.pngdefault: none

To create a ColourImage affector, include a section like this within your particle systemscript:

affector ColourImage{


DeflectorPlane Affector

This affector defines a plane which deflects particles which collide with it. The attributesare:

plane pointA point on the deflector plane. Together with the normal vector it defines theplane.


default: plane point 0 0 0

plane normalThe normal vector of the deflector plane. Together with the point it defines theplane.default: plane normal 0 1 0

bounce The amount of bouncing when a particle is deflected. 0 means no deflectionand 1 stands for 100 percent reflection.default: bounce 1.0

DirectionRandomiser Affector

This affector applies randomness to the movement of the particles. Its extra attributes are:

randomnessThe amount of randomness to introduce in each axial direction.example: randomness 5default: randomness 1

scope The percentage of particles affected in each run of the affector.example: scope 0.5default: scope 1.0

keep velocityDetermines whether the velocity of particles is unchanged.example: keep velocity truedefault: keep velocity false

3.4 Overlay Scripts

Overlay scripts offer you the ability to define overlays in a script which can be reusedeasily. Whilst you could set up all overlays for a scene in code using the methods of theSceneManager, Overlay and OverlayElement classes, in practice it’s a bit unwieldy. Insteadyou can store overlay definitions in text files which can then be loaded whenever required.

Loading scripts

Overlay scripts are loaded at initialisation time by the system: by default it looks in allcommon resource locations (see Root::addResourceLocation) for files with the ’.overlay’extension and parses them. If you want to parse files with a different extension, use theOverlayManager::getSingleton().parseAllSources method with your own extension, or if youwant to parse an individual file, use OverlayManager::getSingleton().parseScript.


Format

Several overlays may be defined in a single script. The script format is pseudo-C++, withsections delimited by curly braces (), comments indicated by starting a line with ’//’ (note,no nested form comments allowed), and inheritance through the use of templates. Thegeneral format is shown below in a typical example:

// The name of the overlay comes firstMyOverlays/ANewOverlay{

zorder 200

container Panel(MyOverlayElements/TestPanel){

// Center it horizontally, put it at the topleft 0.25top 0width 0.5height 0.1material MyMaterials/APanelMaterial

// Another panel nested in this onecontainer Panel(MyOverlayElements/AnotherPanel){

left 0top 0width 0.1height 0.1material MyMaterials/NestedPanel

}}

}

The above example defines a single overlay called ’MyOverlays/ANewOverlay’, with2 panels in it, one nested under the other. It uses relative metrics (the default if nometrics mode option is found).

Every overlay in the script must be given a name, which is the line before the firstopening ’’. This name must be globally unique. It can include path characters (as in theexample) to logically divide up your overlays, and also to avoid duplicate names, but theengine does not treat the name a hierarchical, just as a string. Within the braces are theproperties of the overlay, and any nested elements. The overlay itself only has a singleproperty ’zorder’ which determines how ’high’ it is in the stack of overlays if more than oneis displayed at the same time. Overlays with higher zorder values are displayed on top.


Adding elements to the overlay

Within an overlay, you can include any number of 2D or 3D elements. You do this bydefining a nested block headed by:

’element’ if you want to define a 2D element which cannot have children of it’s own

’container’ if you want to define a 2D container object (which may itself have nested con-tainers or elements)

The element and container blocks are pretty identical apart from their ability to store nestedblocks.

’container’ / ’element’ blocks

These are delimited by curly braces. The format for the header preceding the first brace is:

[container | element] <type name> ( <instance name>) [: <template name>]...

type nameMust resolve to the name of a OverlayElement type which has been registeredwith the OverlayManager. Plugins register with the OverlayManager to ad-vertise their ability to create elements, and at this time advertise the name ofthe type. OGRE comes preconfigured with types ’Panel’, ’BorderPanel’ and’TextArea’.

instance nameMust be a name unique among all other elements / containers by which toidentify the element. Note that you can obtain a pointer to any named elementby calling OverlayManager::getSingleton().getOverlayElement(name).

template nameOptional template on which to base this item. See templates.

The properties which can be included within the braces depend on the custom type.However the following are always valid:• [metrics mode], page 149• [horz align], page 149• [vert align], page 150• [left], page 150• [top], page 151• [width], page 151• [height], page 151• [overlay material], page 152• [caption], page 152


Templates

You can use templates to create numerous elements with the same properties. A template isan abstract element and it is not added to an overlay. It acts as a base class that elements caninherit and get its default properties. To create a template, the keyword ’template’ must bethe first word in the element definition (before container or element). The template elementis created in the topmost scope - it is NOT specified in an Overlay. It is recommended thatyou define templates in a separate overlay though this is not essential. Having templatesdefined in a separate file will allow different look & feels to be easily substituted.

Elements can inherit a template in a similar way to C++ inheritance - by using the :operator on the element definition. The : operator is placed after the closing bracket of thename (separated by a space). The name of the template to inherit is then placed after the: operator (also separated by a space).

A template can contain template children which are created when the template is sub-classed and instantiated. Using the template keyword for the children of a template isoptional but recommended for clarity, as the children of a template are always going to betemplates themselves.

template container BorderPanel(MyTemplates/BasicBorderPanel){

left 0top 0width 1height 1

// setup the texture UVs for a borderpanel

// do this in a template so it doesn’t need to be redone everywherematerial Core/StatsBlockCenterborder_size 0.05 0.05 0.06665 0.06665border_material Core/StatsBlockBorderborder_topleft_uv 0.0000 1.0000 0.1914 0.7969border_top_uv 0.1914 1.0000 0.8086 0.7969border_topright_uv 0.8086 1.0000 1.0000 0.7969border_left_uv 0.0000 0.7969 0.1914 0.2148border_right_uv 0.8086 0.7969 1.0000 0.2148border_bottomleft_uv 0.0000 0.2148 0.1914 0.0000border_bottom_uv 0.1914 0.2148 0.8086 0.0000border_bottomright_uv 0.8086 0.2148 1.0000 0.0000

}template container Button(MyTemplates/BasicButton) : MyTemplates/BasicBorderPanel{


left 0.82top 0.45width 0.16height 0.13material Core/StatsBlockCenterborder_up_material Core/StatsBlockBorder/Upborder_down_material Core/StatsBlockBorder/Down

}template element TextArea(MyTemplates/BasicText){

font_name Ogrechar_height 0.08colour_top 1 1 0colour_bottom 1 0.2 0.2left 0.03top 0.02width 0.12height 0.09

}

MyOverlays/AnotherOverlay{

zorder 490container BorderPanel(MyElements/BackPanel) : MyTemplates/BasicBorderPanel{

left 0top 0width 1height 1

container Button(MyElements/HostButton) : MyTemplates/BasicButton{

left 0.82top 0.45caption MyTemplates/BasicText HOST

}

container Button(MyElements/JoinButton) : MyTemplates/BasicButton{

left 0.82top 0.60caption MyTemplates/BasicText JOIN

}}

}


The above example uses templates to define a button. Note that the button templateinherits from the borderPanel template. This reduces the number of attributes needed toinstantiate a button.

Also note that the instantiate of a Button needs a template name for the caption at-tribute. So templates can also be used by elements that need dynamic creation of childrenelements (the button creates a TextAreaElement in this case for its caption).

See Section 3.4.1 [OverlayElement Attributes], page 149, Section 3.4.2 [Standard Over-layElements], page 153

3.4.1 OverlayElement Attributes

These attributes are valid within the braces of a ’container’ or ’element’ block in an overlayscript. They must each be on their own line. Ordering is unimportant.

metrics mode

Sets the units which will be used to size and position this element.

Format: metrics mode <pixels|relative>Example: metrics mode pixels

This can be used to change the way that all measurement attributes in the rest of thiselement are interpreted. In relative mode, they are interpreted as being a parametric valuefrom 0 to 1, as a proportion of the width / height of the screen. In pixels mode, they aresimply pixel offsets.

Default: metrics mode relative

horz align

Sets the horizontal alignment of this element, in terms of where the horizontal origin is.

Format: horz align <left|center|right>Example: horz align center

This can be used to change where the origin is deemed to be for the purposes of anyhorizontal positioning attributes of this element. By default the origin is deemed to be the


left edge of the screen, but if you change this you can center or right-align your elements.Note that setting the alignment to center or right does not automatically force your elementsto appear in the center or the right edge, you just have to treat that point as the originand adjust your coordinates appropriately. This is more flexible because you can choose toposition your element anywhere relative to that origin. For example, if your element was10 pixels wide, you would use a ’left’ property of -10 to align it exactly to the right edge,or -20 to leave a gap but still make it stick to the right edge.

Note that you can use this property in both relative and pixel modes, but it is mostuseful in pixel mode.

Default: horz align left

vert align

Sets the vertical alignment of this element, in terms of where the vertical origin is.

Format: vert align <top|center|bottom>Example: vert align center

This can be used to change where the origin is deemed to be for the purposes of anyvertical positioning attributes of this element. By default the origin is deemed to be thetop edge of the screen, but if you change this you can center or bottom-align your elements.Note that setting the alignment to center or bottom does not automatically force yourelements to appear in the center or the bottom edge, you just have to treat that point asthe origin and adjust your coordinates appropriately. This is more flexible because youcan choose to position your element anywhere relative to that origin. For example, if yourelement was 50 pixels high, you would use a ’top’ property of -50 to align it exactly to thebottom edge, or -70 to leave a gap but still make it stick to the bottom edge.

Note that you can use this property in both relative and pixel modes, but it is mostuseful in pixel mode.

Default: vert align top

left

Sets the horizontal position of the element relative to it’s parent.


Format: left <value>Example: left 0.5

Positions are relative to the parent (the top-left of the screen if the parent is an overlay,the top-left of the parent otherwise) and are expressed in terms of a proportion of screensize. Therefore 0.5 is half-way across the screen.

Default: left 0

top

Sets the vertical position of the element relative to it’s parent.

Format: top <value>Example: top 0.5

Positions are relative to the parent (the top-left of the screen if the parent is an overlay,the top-left of the parent otherwise) and are expressed in terms of a proportion of screensize. Therefore 0.5 is half-way down the screen.

Default: top 0

width

Sets the width of the element as a proportion of the size of the screen.

Format: width <value>Example: width 0.25

Sizes are relative to the size of the screen, so 0.25 is a quarter of the screen. Sizes arenot relative to the parent; this is common in windowing systems where the top and left arerelative but the size is absolute.

Default: width 1


height

Sets the height of the element as a proportion of the size of the screen.

Format: height <value>Example: height 0.25

Sizes are relative to the size of the screen, so 0.25 is a quarter of the screen. Sizes arenot relative to the parent; this is common in windowing systems where the top and left arerelative but the size is absolute.

Default: height 1

material

Sets the name of the material to use for this element.

Format: material <name>Example: material Examples/TestMaterial

This sets the base material which this element will use. Each type of element may inter-pret this differently; for example the OGRE element ’Panel’ treats this as the backgroundof the panel, whilst ’BorderPanel’ interprets this as the material for the center area only.Materials should be defined in .material scripts.

Note that using a material in an overlay element automatically disables lighting and depthchecking on this material. Therefore you should not use the same material as is used forreal 3D objects for an overlay.

Default: none

caption

Sets a text caption for the element.

Format: caption <string>Example: caption This is a caption


Not all elements support captions, so each element is free to disregard this if it wants.However, a general text caption is so common to many elements that it is included in thegeneric interface to make it simpler to use. This is a common feature in GUI systems.

Default: blank

rotation

Sets the rotation of the element.

Format: rotation <angle in degrees> <axis x> <axis y> <axis z> Example: rotation 300 0 1

Default: none

3.4.2 Standard OverlayElements

Although OGRE’s OverlayElement and OverlayContainer classes are designed to be ex-tended by applications developers, there are a few elements which come as standard withOgre. These include:

• [Panel], page 153• [BorderPanel], page 154• [TextArea], page 154

This section describes how you define their custom attributes in an .overlay script, butyou can also change these custom properties in code if you wish. You do this by callingsetParameter(paramname, value). You may wish to use the StringConverter class to convertyour types to and from strings.

Panel (container)

This is the most bog-standard container you can use. It is a rectangular area which cancontain other elements (or containers) and may or may not have a background, which canbe tiled however you like. The background material is determined by the material attribute,but is only displayed if transparency is off.

Attributes:

transparent <true | false>If set to ’true’ the panel is transparent and is not rendered itself, it is just usedas a grouping level for it’s children.

tiling <layer> <x tile> <y tile>Sets the number of times the texture(s) of the material are tiled across the panelin the x and y direction. <layer> is the texture layer, from 0 to the number of


texture layers in the material minus one. By setting tiling per layer you cancreate some nice multitextured backdrops for your panels, this works especiallywell when you animate one of the layers.

uv coords <topleft u> <topleft v> <bottomright u> <bottomright v>Sets the texture coordinates to use for this panel.

BorderPanel (container)

This is a slightly more advanced version of Panel, where instead of just a single flat panel, thepanel has a separate border which resizes with the panel. It does this by taking an approachvery similar to the use of HTML tables for bordered content: the panel is rendered as 9square areas, with the center area being rendered with the main material (as with Panel)and the outer 8 areas (the 4 corners and the 4 edges) rendered with a separate bordermaterial. The advantage of rendering the corners separately from the edges is that the edgetextures can be designed so that they can be stretched without distorting them, meaningthe single texture can serve any size panel.

Attributes:

border size <left> <right> <top> <bottom>The size of the border at each edge, as a proportion of the size of the screen.This lets you have different size borders at each edge if you like, or you can usethe same value 4 times to create a constant size border.

border material <name>The name of the material to use for the border. This is normally a differentmaterial to the one used for the center area, because the center area is oftentiled which means you can’t put border areas in there. You must put all theimages you need for all the corners and the sides into a single texture.

border topleft uv <u1> <v1> <u2> <v2>[also border topright uv, border bottomleft uv, border bottomright uv]; Thetexture coordinates to be used for the corner areas of the border. 4 coordinatesare required, 2 for the top-left corner of the square, 2 for the bottom-right ofthe square.

border left uv <u1> <v1> <u2> <v2>[also border right uv, border top uv, border bottom uv]; The texture coordi-nates to be used for the edge areas of the border. 4 coordinates are required,2 for the top-left corner, 2 for the bottom-right. Note that you should designthe texture so that the left & right edges can be stretched / squashed verticallyand the top and bottom edges can be stretched / squashed horizontally withoutdetrimental effects.

TextArea (element)

This is a generic element that you can use to render text. It uses fonts which can be definedin code using the FontManager and Font classes, or which have been predefined in .fontdeffiles. See the font definitions section for more information.


Attributes:

font name <name>The name of the font to use. This font must be defined in a .fontdef file toensure it is available at scripting time.

char height <height>The height of the letters as a proportion of the screen height. Character widthsmay vary because OGRE supports proportional fonts, but will be based on thisconstant height.

colour <red> <green> <blue>A solid colour to render the text in. Often fonts are defined in monochrome, sothis allows you to colour them in nicely and use the same texture for multipledifferent coloured text areas. The colour elements should all be expressed asvalues between 0 and 1. If you use predrawn fonts which are already full colourthen you don’t need this.

colour bottom <red> <green> <blue> / colour top <red> <green> <blue>As an alternative to a solid colour, you can colour the text differently at thetop and bottom to create a gradient colour effect which can be very effective.

alignment <left | center | right>Sets the horizontal alignment of the text. This is different from the horz alignparameter.

space width <width>Sets the width of a space in relation to the screen.

3.5 Font Definition Scripts

Ogre uses texture-based fonts to render the TextAreaOverlayElement. You can also use theFont object for your own purpose if you wish. The final form of a font is a Material objectgenerated by the font, and a set of ’glyph’ (character) texture coordinate information.

There are 2 ways you can get a font into OGRE:1. Design a font texture yourself using an art package or font generator tool2. Ask OGRE to generate a font texture based on a truetype font

The former gives you the most flexibility and the best performance (in terms of startuptimes), but the latter is convenient if you want to quickly use a font without having togenerate the texture yourself. I suggest prototyping using the latter and change to theformer for your final solution.

All font definitions are held in .fontdef files, which are parsed by the system at startuptime. Each .fontdef file can contain multiple font definitions. The basic format of an entryin the .fontdef file is:


<font_name>{

type <image | truetype>source <image file | truetype font file>...... custom attributes depending on type

}

Using an existing font texture

If you have one or more artists working with you, no doubt they can produce you a verynice font texture. OGRE supports full colour font textures, or alternatively you can keepthem monochrome / greyscale and use TextArea’s colouring feature. Font textures shouldalways have an alpha channel, preferably an 8-bit alpha channel such as that supported byTGA and PNG files, because it can result in much nicer edges. To use an existing texture,here are the settings you need:

type imageThis just tells OGRE you want a pre-drawn font.

source <filename>This is the name of the image file you want to load. This will be loaded fromthe standard TextureManager resource locations and can be of any type OGREsupports, although JPEG is not recommended because of the lack of alpha andthe lossy compression. I recommend PNG format which has both good losslesscompression and an 8-bit alpha channel.

glyph <character> <u1> <v1> <u2> <v2>This provides the texture coordinates for the specified character. You mustrepeat this for every character you have in the texture. The first 2 numbersare the x and y of the top-left corner, the second two are the x and y of thebottom-right corner. Note that you really should use a common height for allcharacters, but widths can vary because of proportional fonts.

’character’ is either an ASCII character for non-extended 7-bit ASCII, or forextended glyphs, a unicode decimal value, which is identified by preceding thenumber with a ’u’ - e.g. ’u0546’ denotes unicode value 546.

A note for Windows users: I recommend using BitmapFontBuilder(http://www.lmnopc.com/bitmapfontbuilder/), a free tool which will generatea texture and export character widths for you, you can find a tool for converting thebinary output from this into ’glyph’ lines in the Tools folder.

Generating a font texture

You can also generate font textures on the fly using truetype fonts. I don’t recommend heavyuse of this in production work because rendering the texture can take a several seconds perfont which adds to the loading times. However it is a very nice way of quickly getting text

http://www.lmnopc.com/bitmapfontbuilder/


output in a font of your choice.

Here are the attributes you need to supply:

type truetypeTells OGRE to generate the texture from a font

source <ttf file>The name of the ttf file to load. This will be searched for in the commonresource locations and in any resource locations added to FontManager.

size <size in points>The size at which to generate the font, in standard points. Note this onlyaffects how big the characters are in the font texture, not how big they are onthe screen. You should tailor this depending on how large you expect to renderthe fonts because generating a large texture will result in blurry characterswhen they are scaled very small (because of the mipmapping), and converselygenerating a small font will result in blocky characters if large text is rendered.

resolution <dpi>The resolution in dots per inch, this is used in conjunction with the point sizeto determine the final size. 72 / 96 dpi is normal.

antialias colour <true|false>This is an optional flag, which defaults to ’false’. The generator will antialiasthe font by default using the alpha component of the texture, which will lookfine if you use alpha blending to render your text (this is the default assumedby TextAreaOverlayElement for example). If, however you wish to use a colourbased blend like add or modulate in your own code, you should set this to ’true’so the colour values are anti-aliased too. If you set this to true and use alphablending, you’ll find the edges of your font are antialiased too quickly resultingin a ’thin’ look to your fonts, because not only is the alpha blending the edges,the colour is fading too. Leave this option at the default if in doubt.

code points nn-nn [nn-nn] ..This directive allows you to specify which unicode code points should be gen-erated as glyphs into the font texture. If you don’t specify this, code points33-166 will be generated by default which covers the basic Latin 1 glyphs. Ifyou use this flag, you should specify a space-separated list of inclusive codepoint ranges of the form ’start-end’. Numbers must be decimal.

You can also create new fonts at runtime by using the FontManager if you wish.

Chapter 4: Mesh Tools 158

4 Mesh Tools

There are a number of mesh tools available with OGRE to help you manipulate your meshes.

Section 4.1 [Exporters], page 158For getting data out of modellers and into OGRE.

Section 4.2 [XmlConverter], page 159For converting meshes and skeletons to/from XML.

Section 4.3 [MeshUpgrader], page 159For upgrading binary meshes from one version of OGRE to another.

4.1 Exporters

Exporters are plugins to 3D modelling tools which write meshes and skeletal animation tofile formats which OGRE can use for realtime rendering. The files the exporters write endin .mesh and .skeleton respectively.

Each exporter has to be written specifically for the modeller in question, although they alluse a common set of facilities provided by the classes MeshSerializer and SkeletonSerializer.They also normally require you to own the modelling tool.

All the exporters here can be built from the source code, or you can download precom-piled versions from the OGRE web site.

A Note About Modelling / Animation For OGRE

There are a few rules when creating an animated model for OGRE:

• You must have no more than 4 weighted bone assignments per vertex. If you havemore, OGRE will eliminate the lowest weighted assignments and re-normalise the otherweights. This limit is imposed by hardware blending limitations.

• All vertices must be assigned to at least one bone - assign static vertices to the rootbone.

• At the very least each bone must have a keyframe at the beginning and end of theanimation.

If you’re creating unanimated meshes, then you do not need to be concerned with theabove.

Full documentation for each exporter is provided along with the exporter itself,and there is a list of the currently supported modelling tools in the OGRE Wiki athttp://www.ogre3d.org/wiki/index.php/Exporters.

http://www.ogre3d.org/wiki/index.php/Exporters

Chapter 4: Mesh Tools 159

4.2 XmlConverter

The OgreXmlConverter tool can converter binary .mesh and .skeleton files to XML and backagain - this is a very useful tool for debugging the contents of meshes, or for exchangingmesh data easily - many of the modeller mesh exporters export to XML because it is simplerto do, and OgreXmlConverter can then produce a binary from it. Other than simplicity,the other advantage is that OgreXmlConverter can generate additional information for themesh, like bounding regions and level-of-detail reduction.

Syntax:Usage: OgreXMLConverter sourcefile [destfile]sourcefile = name of file to convertdestfile = optional name of file to write to. If you don’t

specify this OGRE works it out through the extensionand the XML contents if the source is XML. For exampletest.mesh becomes test.xml, test.xml becomes test.meshif the XML document root is <mesh> etc.

When converting XML to .mesh, you will be prompted to (re)generate level-of-detail(LOD) information for the mesh - you can choose to skip this part if you wish, butdoing it will allow you to make your mesh reduce in detail automatically when it is loadedinto the engine. The engine uses a complex algorithm to determine the best parts of themesh to reduce in detail depending on many factors such as the curvature of the surface,the edges of the mesh and seams at the edges of textures and smoothing groups - takingadvantage of it is advised to make your meshes more scalable in real scenes.

4.3 MeshUpgrader

This tool is provided to allow you to upgrade your meshes when the binary format changes- sometimes we alter it to add new features and as such you need to keep your own assetsup to date. This tools has a very simple syntax:OgreMeshUpgrade <oldmesh> <newmesh>

The OGRE release notes will notify you when this is necessary with a new release.

Chapter 5: Hardware Buffers 160

5 Hardware Buffers

Vertex buffers, index buffers and pixel buffers inherit most of their features from the Hard-wareBuffer class. The general premise with a hardware buffer is that it is an area of memorywith which you can do whatever you like; there is no format (vertex or otherwise) associatedwith the buffer itself - that is entirely up to interpretation by the methods that use it - inthat way, a HardwareBuffer is just like an area of memory you might allocate using ’malloc’- the difference being that this memory is likely to be located in GPU or AGP memory.

5.1 The Hardware Buffer Manager

The HardwareBufferManager class is the factory hub of all the objects in the new ge-ometry system. You create and destroy the majority of the objects you use to definegeometry through this class. It’s a Singleton, so you access it by doing HardwareBuffer-Manager::getSingleton() - however be aware that it is only guaranteed to exist after theRenderSystem has been initialised (after you call Root::initialise); this is because the ob-jects created are invariably API-specific, although you will deal with them through onecommon interface.

For example:VertexDeclaration* decl = HardwareBufferManager::getSingleton().createVertexDeclaration();

HardwareVertexBufferSharedPtr vbuf =HardwareBufferManager::getSingleton().createVertexBuffer(

3*sizeof(Real), // size of one whole vertexnumVertices, // number of verticesHardwareBuffer::HBU_STATIC_WRITE_ONLY, // usagefalse); // no shadow buffer

Don’t worry about the details of the above, we’ll cover that in the later sections. The im-portant thing to remember is to always create objects through the HardwareBufferManager,don’t use ’new’ (it won’t work anyway in most cases).

5.2 Buffer Usage

Because the memory in a hardware buffer is likely to be under significant contention duringthe rendering of a scene, the kind of access you need to the buffer over the time it is usedis extremely important; whether you need to update the contents of the buffer regularly,whether you need to be able to read information back from it, these are all importantfactors to how the graphics card manages the buffer. The method and exact parametersused to create a buffer depends on whether you are creating an index or vertex buffer(See Section 5.6 [Hardware Vertex Buffers], page 163 and See Section 5.7 [Hardware IndexBuffers], page 168), however one creation parameter is common to them both - the ’usage’.

The most optimal type of hardware buffer is one which is not updated often, and is neverread from. The usage parameter of createVertexBuffer or createIndexBuffer can be one ofthe following:


HBU_STATICThis means you do not need to update the buffer very often, but you mightoccasionally want to read from it.

HBU_STATIC_WRITE_ONLYThis means you do not need to update the buffer very often, and you do notneed to read from it. However, you may read from it’s shadow buffer if you setone up (See Section 5.3 [Shadow Buffers], page 161). This is the optimal bufferusage setting.

HBU_DYNAMICThis means you expect to update the buffer often, and that you may wish toread from it. This is the least optimal buffer setting.

HBU_DYNAMIC_WRITE_ONLYThis means you expect to update the buffer often, but that you never wantto read from it. However, you may read from it’s shadow buffer if you setone up (See Section 5.3 [Shadow Buffers], page 161). If you use this option,and replace the entire contents of the buffer every frame, then you shoulduse HBU DYNAMIC WRITE ONLY DISCARDABLE instead, since that hasbetter performance characteristics on some platforms.

HBU_DYNAMIC_WRITE_ONLY_DISCARDABLEThis means that you expect to replace the entire contents of the buffer on an ex-tremely regular basis, most likely every frame. By selecting this option, you freethe system up from having to be concerned about losing the existing contents ofthe buffer at any time, because if it does lose them, you will be replacing themnext frame anyway. On some platforms this can make a significant performancedifference, so you should try to use this whenever you have a buffer you needto update regularly. Note that if you create a buffer this way, you should usethe HBL DISCARD flag when locking the contents of it for writing.

Choosing the usage of your buffers carefully is important to getting optimal performanceout of your geometry. If you have a situation where you need to update a vertex bufferoften, consider whether you actually need to update all the parts of it, or just some. If it’sthe latter, consider using more than one buffer, with only the data you need to modify inthe HBU DYNAMIC buffer.

Always try to use the WRITE ONLY forms. This just means that you cannot read directlyfrom the hardware buffer, which is good practice because reading from hardware buffers isvery slow. If you really need to read data back, use a shadow buffer, described in the nextsection.

5.3 Shadow Buffers

As discussed in the previous section, reading data back from a hardware buffer performsvery badly. However, if you have a cast-iron need to read the contents of the vertex buffer,you should set the ’shadowBuffer’ parameter of createVertexBuffer or createIndexBuffer to’true’. This causes the hardware buffer to be backed with a system memory copy, whichyou can read from with no more penalty than reading ordinary memory. The catch is that


when you write data into this buffer, it will first update the system memory copy, then itwill update the hardware buffer, as separate copying process - therefore this technique hasan additional overhead when writing data. Don’t use it unless you really need it.

5.4 Locking buffers

In order to read or update a hardware buffer, you have to ’lock’ it. This performs 2 functions- it tells the card that you want access to the buffer (which can have an effect on its renderingqueue), and it returns a pointer which you can manipulate. Note that if you’ve asked toread the buffer (and remember, you really shouldn’t unless you’ve set the buffer up witha shadow buffer), the contents of the hardware buffer will have been copied into systemmemory somewhere in order for you to get access to it. For the same reason, when you’refinished with the buffer you must unlock it; if you locked the buffer for writing this willtrigger the process of uploading the modified information to the graphics hardware.

Lock parameters

When you lock a buffer, you call one of the following methods:// Lock the entire bufferpBuffer->lock(lockType);// Lock only part of the bufferpBuffer->lock(start, length, lockType);

The first call locks the entire buffer, the second locks only the section from ’start’ (asa byte offset), for ’length’ bytes. This could be faster than locking the entire buffer sinceless is transferred, but not if you later update the rest of the buffer too, because doing it insmall chunks like this means you cannot use HBL DISCARD (see below).

The lockType parameter can have a large effect on the performance of your application,especially if you are not using a shadow buffer.

HBL_NORMALThis kind of lock allows reading and writing from the buffer - it’s also the leastoptimal because basically you’re telling the card you could be doing anything atall. If you’re not using a shadow buffer, it requires the buffer to be transferredfrom the card and back again. If you’re using a shadow buffer the effect isminimal.

HBL_READ_ONLYThis means you only want to read the contents of the buffer. Best used whenyou created the buffer with a shadow buffer because in that case the data doesnot have to be downloaded from the card.

HBL_DISCARDThis means you are happy for the card to discard the entire current contentsof the buffer. Implicitly this means you are not going to read the data - italso means that the card can avoid any stalls if the buffer is currently being


rendered from, because it will actually give you an entirely different one. Usethis wherever possible when you are locking a buffer which was not created witha shadow buffer. If you are using a shadow buffer it matters less, although witha shadow buffer it’s preferable to lock the entire buffer at once, because thatallows the shadow buffer to use HBL DISCARD when it uploads the updatedcontents to the real buffer.

HBL_NO_OVERWRITEThis is useful if you are locking just part of the buffer and thus cannot useHBL DISCARD. It tells the card that you promise not to modify any sectionof the buffer which has already been used in a rendering operation this frame.Again this is only useful on buffers with no shadow buffer.

Once you have locked a buffer, you can use the pointer returned however you wish (justdon’t bother trying to read the data that’s there if you’ve used HBL DISCARD, or writethe data if you’ve used HBL READ ONLY). Modifying the contents depends on the type ofbuffer, See Section 5.6 [Hardware Vertex Buffers], page 163 and See Section 5.7 [HardwareIndex Buffers], page 168

5.5 Practical Buffer Tips

The interplay of usage mode on creation, and locking options when reading / updating isimportant for performance. Here’s some tips:

1. Aim for the ’perfect’ buffer by creating with HBU STATIC WRITE ONLY, with noshadow buffer, and locking all of it once only with HBL DISCARD to populate it.Never touch it again.

2. If you need to update a buffer regularly, you will have to compromise. UseHBU DYNAMIC WRITE ONLY when creating (still no shadow buffer),and use HBL DISCARD to lock the entire buffer, or if you can’t then useHBL NO OVERWRITE to lock parts of it.

3. If you really need to read data from the buffer, create it with a shadow buffer. Makesure you use HBL READ ONLY when locking for reading because it will avoid theupload normally associated with unlocking the buffer. You can also combine this witheither of the 2 previous points, obviously try for static if you can - remember that theWRITE ONLY’ part refers to the hardware buffer so can be safely used with a shadow

buffer you read from.

4. Split your vertex buffers up if you find that your usage patterns for different elementsof the vertex are different. No point having one huge updateable buffer with all thevertex data in it, if all you need to update is the texture coordinates. Split that partout into it’s own buffer and make the rest HBU STATIC WRITE ONLY.

5.6 Hardware Vertex Buffers

This section covers specialised hardware buffers which contain vertex data. For a generaldiscussion of hardware buffers, along with the rules for creating and locking them, see theChapter 5 [Hardware Buffers], page 160 section.


5.6.1 The VertexData class

The VertexData class collects together all the vertex-related information used to rendergeometry. The new RenderOperation requires a pointer to a VertexData object, and it isalso used in Mesh and SubMesh to store the vertex positions, normals, texture coordinatesetc. VertexData can either be used alone (in order to render unindexed geometry, wherethe stream of vertices defines the triangles), or in combination with IndexData where thetriangles are defined by indexes which refer to the entries in VertexData.

It’s worth noting that you don’t necessarily have to use VertexData to store your applica-tions geometry; all that is required is that you can build a VertexData structure when itcomes to rendering. This is pretty easy since all of VertexData’s members are pointers, soyou could maintain your vertex buffers and declarations in alternative structures if you like,so long as you can convert them for rendering.

The VertexData class has a number of important members:

vertexStartThe position in the bound buffers to start reading vertex data from. This allowsyou to use a single buffer for many different renderables.

vertexCountThe number of vertices to process in this particular rendering group

vertexDeclarationA pointer to a VertexDeclaration object which defines the format of the vertexinput; note this is created for you by VertexData. See Section 5.6.2 [VertexDeclarations], page 164

vertexBufferBindingA pointer to a VertexBufferBinding object which defines which vertex buffersare bound to which sources - again, this is created for you by VertexData. SeeSection 5.6.3 [Vertex Buffer Bindings], page 166

5.6.2 Vertex Declarations

Vertex declarations define the vertex inputs used to render the geometry you want to appearon the screen. Basically this means that for each vertex, you want to feed a certain set ofdata into the graphics pipeling, which (you hope) will affect how it all looks when thetriangles are drawn. Vertex declarations let you pull items of data (which we call vertexelements, represented by the VertexElement class) from any number of buffers, both sharedand dedicated to that particular element. It’s your job to ensure that the contents of thebuffers make sense when interpreted in the way that your VertexDeclaration indicates thatthey should.

To add an element to a VertexDeclaration, you call it’s addElement method. The parametersto this method are:

source This tells the declaration which buffer the element is to be pulled from. Notethat this is just an index, which may range from 0 to one less than the numberof buffers which are being bound as sources of vertex data. See Section 5.6.3


[Vertex Buffer Bindings], page 166 for information on how a real buffer is boundto a source index. Storing the source of the vertex element this way (ratherthan using a buffer pointer) allows you to rebind the source of a vertex veryeasily, without changing the declaration of the vertex format itself.

offset Tells the declaration how far in bytes the element is offset from the start ofeach whole vertex in this buffer. This will be 0 if this is the only element beingsourced from this buffer, but if other elements are there then it may be higher.A good way of thinking of this is the size of all vertex elements which precedethis element in the buffer.

type This defines the data type of the vertex input, including it’s size. This isan important element because as GPUs become more advanced, we can nolonger assume that position input will always require 3 floating point numbers,because programmable vertex pipelines allow full control over the inputs andoutuputs. This part of the element definition covers the basic type and size,e.g. VET FLOAT3 is 3 floating point numbers - the meaning of the data isdealt with in the next paramter.

semantic This defines the meaning of the element - the GPU will use this to determinewhat to use this input for, and programmable vertex pipelines will use this toidentify which semantic to map the input to. This can identify the elementas positional data, normal data, texture coordinate data, etc. See the APIreference for full details of all the options.

index This parameter is only required when you supply more than one element ofthe same semantic in one vertex declaration. For example, if you supply morethan one set of texture coordinates, you would set first sets index to 0, and thesecond set to 1.

You can repeat the call to addElement for as many elements as you have in your vertexinput structures. There are also useful methods on VertexDeclaration for locating elementswithin a declaration - see the API reference for full details.

Important Considerations

Whilst in theory you have completely full reign over the format of you vertices, in realitythere are some restrictions. Older DirectX hardware imposes a fixed ordering on the ele-ments which are pulled from each buffer; specifically any hardware prior to DirectX 9 mayimpose the following restrictions:

• VertexElements should be added in the following order, and the order of the elementswithin any shared buffer should be as follows:

1. Positions

2. Blending weights

3. Normals

4. Diffuse colours

5. Specular colours

6. Texture coordinates (starting at 0, listed in order, with no gaps)


• You must not have unused gaps in your buffers which are not referenced by any Ver-texElement

• You must not cause the buffer & offset settings of 2 VertexElements to overlap

OpenGL and DirectX 9 compatible hardware are not required to follow these strictlimitations, so you might find, for example that if you broke these rules your applicationwould run under OpenGL and under DirectX on recent cards, but it is not guaranteed torun on older hardware under DirectX unless you stick to the above rules. For this reasonyou’re advised to abide by them!

5.6.3 Vertex Buffer Bindings

Vertex buffer bindings are about associating a vertex buffer with a source index used inSection 5.6.2 [Vertex Declarations], page 164.

Creating the Vertex Buffer

Firstly, lets look at how you create a vertex buffer:HardwareVertexBufferSharedPtr vbuf =

HardwareBufferManager::getSingleton().createVertexBuffer(3*sizeof(Real), // size of one whole vertexnumVertices, // number of verticesHardwareBuffer::HBU_STATIC_WRITE_ONLY, // usagefalse); // no shadow buffer

Notice that we use Section 5.1 [The Hardware Buffer Manager], page 160 to create ourvertex buffer, and that a class called HardwareVertexBufferSharedPtr is returned from themethod, rather than a raw pointer. This is because vertex buffers are reference counted -you are able to use a single vertex buffer as a source for multiple pieces of geometry thereforea standard pointer would not be good enough, because you would not know when all thedifferent users of it had finished with it. The HardwareVertexBufferSharedPtr class managesits own destruction by keeping a reference count of the number of times it is being used -when the last HardwareVertexBufferSharedPtr is destroyed, the buffer itself automaticallydestroys itself.

The parameters to the creation of a vertex buffer are as follows:

vertexSize The size in bytes of a whole vertex in this buffer. A vertex may include multipleelements, and in fact the contents of the vertex data may be reinterpreted bydifferent vertex declarations if you wish. Therefore you must tell the buffermanager how large a whole vertex is, but not the internal format of the vertex,since that is down to the declaration to interpret. In the above example, thesize is set to the size of 3 floating point values - this would be enough to holda standard 3D position or normal, or a 3D texture coordinate, per vertex.

numVerticesThe number of vertices in this buffer. Remember, not all the vertices have tobe used at once - it can be beneficial to create large buffers which are sharedbetween many chunks of geometry because changing vertex buffer bindings isa render state switch, and those are best minimised.


usage This tells the system how you intend to use the buffer. See Section 5.2 [BufferUsage], page 160

useShadowBufferTells the system whether you want this buffer backed by a system-memory copy.See Section 5.3 [Shadow Buffers], page 161

Binding the Vertex Buffer

The second part of the process is to bind this buffer which you have created to a sourceindex. To do this, you call:vertexBufferBinding->setBinding(0, vbuf);

This results in the vertex buffer you created earlier being bound to source index 0, soany vertex element which is pulling its data from source index 0 will retrieve data from thisbuffer.

There are also methods for retrieving buffers from the binding data - see the API referencefor full details.

5.6.4 Updating Vertex Buffers

The complexity of updating a vertex buffer entirely depends on how its contents are laidout. You can lock a buffer (See Section 5.4 [Locking buffers], page 162), but how you writedata into it vert much depends on what it contains.

Lets start with a vert simple example. Lets say you have a buffer which only contains vertexpositions, so it only contains sets of 3 floating point numbers per vertex. In this case, allyou need to do to write data into it is:Real* pReal = static_cast<Real*>(vbuf->lock(HardwareBuffer::HBL_DISCARD));

... then you just write positions in chunks of 3 reals. If you have other floating pointdata in there, it’s a little more complex but the principle is largely the same, you just needto write alternate elements. But what if you have elements of different types, or you needto derive how to write the vertex data from the elements themselves? Well, there are someuseful methods on the VertexElement class to help you out.

Firstly, you lock the buffer but assign the result to a unsigned char* rather thana specific type. Then, for each element whcih is sourcing from this buffer (whichyou can find out by calling VertexDeclaration::findElementsBySource) you callVertexElement::baseVertexPointerToElement. This offsets a pointer which points at thebase of a vertex in a buffer to the beginning of the element in question, and allows you touse a pointer of the right type to boot. Here’s a full example:// Get base pointerunsigned char* pVert = static_cast<unsigned char*>(vbuf->lock(HardwareBuffer::HBL_READ_ONLY));Real* pReal;for (size_t v = 0; v < vertexCount; ++v){

// Get elementsVertexDeclaration::VertexElementList elems = decl->findElementsBySource(bufferIdx);


VertexDeclaration::VertexElementList::iterator i, iend;for (i = elems.begin(); i != elems.end(); ++i){

VertexElement& elem = *i;if (elem.getSemantic() == VES_POSITION){

elem.baseVertexPointerToElement(pVert, &pReal);// write position using pReal

}

...

}pVert += vbuf->getVertexSize();

}vbuf->unlock();

See the API docs for full details of all the helper methods on VertexDeclaration andVertexElement to assist you in manipulating vertex buffer data pointers.

5.7 Hardware Index Buffers

Index buffers are used to render geometry by building triangles out of vertices indirectly byreference to their position in the buffer, rather than just building triangles by sequentiallyreading vertices. Index buffers are simpler than vertex buffers, since they are just a list ofindexes at the end of the day, howeverthey can be held on the hardware and shared betweenmultiple pieces of geometry in the same way vertex buffers can, so the rules on creation andlocking are the same. See Chapter 5 [Hardware Buffers], page 160 for information.

5.7.1 The IndexData class

This class summarises the information required to use a set of indexes to render geometry.It’s members are as follows:

indexStart The first index used by this piece of geometry; this can be useful for sharing asingle index buffer among several geometry pieces.

indexCountThe number of indexes used by this particular renderable.

indexBufferThe index buffer which is used to source the indexes.

Creating an Index Buffer

Index buffers are created using See Section 5.1 [The Hardware Buffer Manager], page 160just like vertex buffers, here’s how:HardwareIndexBufferSharedPtr ibuf = HardwareBufferManager::getSingleton().

createIndexBuffer(


HardwareIndexBuffer::IT_16BIT, // type of indexnumIndexes, // number of indexesHardwareBuffer::HBU_STATIC_WRITE_ONLY, // usagefalse); // no shadow buffer

Once again, notice that the return type is a class rather than a pointer; this is referencecounted so that the buffer is automatically destroyed when no more references are made toit. The parameters to the index buffer creation are:

indexType There are 2 types of index; 16-bit and 32-bit. They both perform the same way,except that the latter can address larger vertex buffers. If your buffer includesmore than 65526 vertices, then you will need to use 32-bit indexes. Note thatyou should only use 32-bit indexes when you need to, since they incur moreoverhead than 16-bit vertices, and are not supported on some older hardware.

numIndexesThe number of indexes in the buffer. As with vertex buffers, you should considerwhether you can use a shared index buffer which is used by multiple pieces ofgeometry, since there can be performance advantages to switching index buffersless often.

usage This tells the system how you intend to use the buffer. See Section 5.2 [BufferUsage], page 160

useShadowBufferTells the system whether you want this buffer backed by a system-memory copy.See Section 5.3 [Shadow Buffers], page 161

5.7.2 Updating Index Buffers

Updating index buffers can only be done when you lock the buffer for writing; See Section 5.4[Locking buffers], page 162 for details. Locking returns a void pointer, which must be cast tothe apropriate type; with index buffers this is either an unsigned short (for 16-bit indexes)or an unsigned long (for 32-bit indexes). For example:unsigned short* pIdx = static_cast<unsigned short*>(ibuf->lock(HardwareBuffer::HBL_DISCARD));

You can then write to the buffer using the usual pointer semantics, just remember tounlock the buffer when you’re finished!

5.8 Hardware Pixel Buffers

Hardware Pixel Buffers are a special kind of buffer that stores graphical data in graphicscard memory, generally for use as textures. Pixel buffers can represent a one dimensional,two dimensional or three dimensional image. A texture can consist of a multiple of thesebuffers.

In contrary to vertex and index buffers, pixel buffers are not constructed directly. Whencreating a texture, the necessary pixel buffers to hold its data are constructed automatically.

5.8.1 Textures

A texture is an image that can be applied onto the surface of a three dimensional model.In Ogre, textures are represented by the Texture resource class.


Creating a texture

Textures are created through the TextureManager. In most cases they are created fromimage files directly by the Ogre resource system. If you are reading this, you most probablywant to create a texture manually so that you can provide it with image data yourself. Thisis done through TextureManager::createManual:ptex = TextureManager::getSingleton().createManual(

"MyManualTexture", // Name of texture"General", // Name of resource group in which the texture should be createdTEX_TYPE_2D, // Texture type256, // Width256, // Height1, // Depth (Must be 1 for two dimensional textures)0, // Number of mipmapsPF_A8R8G8B8, // Pixel formatTU_DYNAMIC_WRITE_ONLY // usage

);

This example creates a texture named MyManualTexture in resource group General. Itis a square two dimensional texture, with width 256 and height 256. It has no mipmaps,internal format PF A8R8G8B8 and usage TU DYNAMIC WRITE ONLY.

The different texture types will be discussed in Section 5.8.3 [Texture Types], page 172.Pixel formats are summarised in Section 5.8.4 [Pixel Formats], page 173.

Texture usages

In addition to the hardware buffer usages as described in See Section 5.2 [Buffer Usage],page 160 there are some usage flags specific to textures:

TU AUTOMIPMAPMipmaps for this texture will be automatically generated by the graphics hard-ware. The exact algorithm used is not defined, but you can assume it to be a2x2 box filter.

TU RENDERTARGETThis texture will be a render target, ie. used as a target for render to texture.Setting this flag will ignore all other texture usages except TU AUTOMIPMAP.

TU DEFAULTThis is actualy a combination of usage flags, and is equivalent toTU AUTOMIPMAP | TU STATIC WRITE ONLY. The resource systemuses these flags for textures that are loaded from images.

Getting a PixelBuffer

A Texture can consist of multiple PixelBuffers, one for each combo if mipmap level and facenumber. To get a PixelBuffer from a Texture object the method Texture::getBuffer(face,mipmap) is used:

face should be zero for non-cubemap textures. For cubemap textures it identifies theface to use, which is one of the cube faces described in See Section 5.8.3 [Texture Types],page 172.


mipmap is zero for the zeroth mipmap level, one for the first mipmap level, and so on.On textures that have automatic mipmap generation (TU AUTOMIPMAP) only level 0should be accessed, the rest will be taken care of by the rendering API.

A simple example of using getBuffer is// Get the PixelBuffer for face 0, mipmap 0.HardwarePixelBufferSharedPtr ptr = tex->getBuffer(0,0);

5.8.2 Updating Pixel Buffers

Pixel Buffers can be updated in two different ways; a simple, convient way and a moredifficult (but in some cases faster) method. Both methods make use of PixelBox objects(See Section 5.8.5 [Pixel boxes], page 174) to represent image data in memory.

blitFromMemory

The easy method to get an image into a PixelBuffer is by using HardwarePixel-Buffer::blitFromMemory. This takes a PixelBox object and does all necessary pixel formatconversion and scaling for you. For example, to create a manual texture and load an imageinto it, all you have to do is// Manually loads an image and puts the contents in a manually created textureImage img;img.load("elephant.png", "General");// Create RGB texture with 5 mipmapsTexturePtr tex = TextureManager::getSingleton().createManual(

"elephant","General",TEX_TYPE_2D,img.getWidth(), img.getHeight(),5, PF_X8R8G8B8);

// Copy face 0 mipmap 0 of the image to face 0 mipmap 0 of the texture.tex->getBuffer(0,0)->blitFromMemory(img.getPixelBox(0,0));

Direct memory locking

A more advanced method to transfer image data from and to a PixelBuffer is to use locking.By locking a PixelBuffer you can directly access its contents in whatever the internal formatof the buffer inside the GPU is./// Lock the buffer so we can write to itbuffer->lock(HardwareBuffer::HBL_DISCARD);const PixelBox &pb = buffer->getCurrentLock();

/// Update the contents of pb here/// Image data starts at pb.data and has format pb.format/// Here we assume data.format is PF_X8R8G8B8 so we can address pixels as uint32.uint32 *data = static_cast<uint32*>(pb.data);size_t height = pb.getHeight();size_t width = pb.getWidth();size_t pitch = pb.rowPitch; // Skip between rows of imagefor(size_t y=0; y<height; ++y)


{for(size_t x=0; x<width; ++x)

{// 0xRRGGBB -> fill the buffer with yellow pixelsdata[pitch*y + x] = 0x00FFFF00;

}}

/// Unlock the buffer again (frees it for use by the GPU)buffer->unlock();

5.8.3 Texture Types

There are four types of textures supported by current hardware, three of them only differin the amount of dimensions they have (one, two or three). The fourth one is special. Thedifferent texture types are:

TEX TYPE 1DOne dimensional texture, used in combination with 1D texture coordinates.

TEX TYPE 2DTwo dimensional texture, used in combination with 2D texture coordinates.

TEX TYPE 3DThree dimensional volume texture, used in combination with 3D texture coor-dinates.

TEX TYPE CUBE MAPCube map (six two dimensional textures, one for each cube face), used in com-bination with 3D texture coordinates.

Cube map textures

The cube map texture type (TEX TYPE CUBE MAP) is a different beast from the others;a cube map texture represents a series of six two dimensional images addressed by 3D texturecoordinates.

+X (face 0)Represents the positive x plane (right).

-X (face 1)Represents the negative x plane (left).

+Y (face 2)Represents the positive y plane (top).

-Y (face 3)Represents the negative y plane (bottom).

+Z (face 4)Represents the positive z plane (front).

-Z (face 5) Represents the negative z plane (back).


5.8.4 Pixel Formats

A pixel format described the storage format of pixel data. It defines the way pixels areencoded in memory. The following classes of pixel formats (PF *) are defined:

Native endian formats (PF A8R8G8B8 and other formats with bit counts)These are native endian (16, 24 and 32 bit) integers in memory. This meansthat an image with format PF A8R8G8B8 can be seen as an array of 32 bitintegers, defined as 0xAARRGGBB in hexadecimal. The meaning of the lettersis described below.

Byte formats (PF BYTE *)These formats have one byte per channel, and their channels in memory areorganized in the order they are specified in the format name. For example,PF BYTE RGBA consists of blocks of four bytes, one for red, one for green,one for blue, one for alpha.

Short formats (PF SHORT *)These formats have one unsigned short (16 bit integer) per channel, and theirchannels in memory are organized in the order they are specified in the for-mat name. For example, PF SHORT RGBA consists of blocks of four 16 bitintegers, one for red, one for green, one for blue, one for alpha.

Float16 formats (PF FLOAT16 *)These formats have one 16 bit floating point number per channel, and theirchannels in memory are organized in the order they are specified in the formatname. For example, PF FLOAT16 RGBA consists of blocks of four 16 bitfloats, one for red, one for green, one for blue, one for alpha. The 16 bit floats,also called half float) are very similar to the IEEE single-precision floating-pointstandard of the 32 bits floats, except that they have only 5 exponent bits and10 mantissa. Note that there is no standard C++ data type or CPU supportto work with these efficiently, but GPUs can calculate with these much moreefficiently than with 32 bit floats.

Float32 formats (PF FLOAT32 *)These formats have one 32 bit floating point number per channel, and theirchannels in memory are organized in the order they are specified in the formatname. For example, PF FLOAT32 RGBA consists of blocks of four 32 bitfloats, one for red, one for green, one for blue, one for alpha. The C++ datatype for these 32 bits floats is just "float".

Compressed formats (PF DXT[1-5])S3TC compressed texture formats, a good description can be found at |Wikipedia (http://en.wikipedia.org/wiki/S3TC)

Colour channels

The meaning of the channels R,G,B,A,L and X is defined as

R Red colour component, usually ranging from 0.0 (no red) to 1.0 (full red).

G Green colour component, usually ranging from 0.0 (no green) to 1.0 (full green).

B Blue colour component, usually ranging from 0.0 (no blue) to 1.0 (full blue).


A Alpha component, usually ranging from 0.0 (entire transparent) to 1.0 (opaque).

L Luminance component, usually ranging from 0.0 (black) to 1.0 (white). Theluminance component is duplicated in the R, G, and B channels to achieve agreyscale image.

X This component is completely ignored.

If none of red, green and blue components, or luminance is defined in a format, thesedefault to 0. For the alpha channel this is different; if no alpha is defined, it defaults to 1.

Complete list of pixel formats

This pixel formats supported by the current version of Ogre are

Byte formatsPF BYTE RGB, PF BYTE BGR, PF BYTE BGRA, PF BYTE RGBA,PF BYTE L, PF BYTE LA, PF BYTE A

Short formatsPF SHORT RGBA

Float16 formatsPF FLOAT16 R, PF FLOAT16 RGB, PF FLOAT16 RGBA

Float32 formatsPF FLOAT32 R, PF FLOAT32 RGB, PF FLOAT32 RGBA

8 bit native endian formatsPF L8, PF A8, PF A4L4, PF R3G3B2

16 bit native endian formatsPF L16, PF R5G6B5, PF B5G6R5, PF A4R4G4B4, PF A1R5G5B5

24 bit native endian formatsPF R8G8B8, PF B8G8R8

32 bit native endian formatsPF A8R8G8B8, PF A8B8G8R8, PF B8G8R8A8, PF R8G8B8A8,PF X8R8G8B8, PF X8B8G8R8, PF A2R10G10B10 PF A2B10G10R10

Compressed formatsPF DXT1, PF DXT2, PF DXT3, PF DXT4, PF DXT5

5.8.5 Pixel boxes

All methods in Ogre that take or return raw image data return a PixelBox object.A PixelBox is a primitive describing a volume (3D), image (2D) or line (1D) of pixels

in CPU memory. It describes the location and data format of a region of memory used forimage data, but does not do any memory management in itself.

Inside the memory pointed to by the data member of a pixel box, pixels are stored asa succession of "depth" slices (in Z), each containing "height" rows (Y) of "width" pixels(X).

Dimensions that are not used must be 1. For example, a one dimensional image willhave extents (width,1,1). A two dimensional image has extents (width,height,1).

A PixelBox has the following members:


data The pointer to the first component of the image data in memory.

format The pixel format (See Section 5.8.4 [Pixel Formats], page 173) of the imagedata.

rowPitch The number of elements between the leftmost pixel of one row and the left pixelof the next. This value must always be equal to getWidth() (consecutive) forcompressed formats.

slicePitch The number of elements between the top left pixel of one (depth) slice andthe top left pixel of the next. Must be a multiple of rowPitch. This valuemust always be equal to getWidth()*getHeight() (consecutive) for compressedformats.

left, top, right, bottom, front, backExtents of the box in three dimensional integer space. Note that the left, top,and front edges are included but the right, bottom and top ones are not. leftmust always be smaller or equal to right, top must always be smaller or equalto bottom, and front must always be smaller or equal to back.

It also has some useful methods:

getWidth()Get the width of this box

getHeight()Get the height of this box. This is 1 for one dimensional images.

getDepth()Get the depth of this box. This is 1 for one and two dimensional images.

setConsecutive()Set the rowPitch and slicePitch so that the buffer is laid out consecutive inmemory.

getRowSkip()Get the number of elements between one past the rightmost pixel of one rowand the leftmost pixel of the next row. This is zero if rows are consecutive.

getSliceSkip()Get the number of elements between one past the right bottom pixel of one sliceand the left top pixel of the next slice. This is zero if slices are consecutive.

isConsecutive()Return whether this buffer is laid out consecutive in memory (ie the pitches areequal to the dimensions)

getConsecutiveSize()Return the size (in bytes) this image would take if it was laid out consecutivein memory

getSubVolume(const Box &def)Return a subvolume of this PixelBox, as a PixelBox.

For more information about these methods consult the API documentation.

Chapter 6: External Texture Sources 176

6 External Texture Sources

Introduction

This tutorial will provide a brief introduction of ExternalTextureSource and ExternalTex-tureSourceManager classes, their relationship, and how the PlugIns work. For those inter-ested in developing a Texture Source Plugin or maybe just wanting to know more aboutthis system, take a look the ffmpegVideoSystem plugin, which you can find more about onthe OGRE forums.

What Is An External Texture Source?

What is a texture source? Well, a texture source could be anything - png, bmp, jpeg,etc. However, loading textures from traditional bitmap files is already handled by anotherpart OGRE. There are, however, other types of sources to get texture data from - i.e.mpeg/avi/etc movie files, flash, run-time generated source, user defined, etc.

How do external texture source plugins benefit OGRE? Well, the main answer is: addingsupport for any type of texture source does not require changing OGRE to support it...all that is involved is writing a new plugin. Additionally, because the manager uses theStringInterface class to issue commands/params, no change to the material script readeris needs to be made. As a result, if a plugin needs a special parameter set, it just createsa new command in it’s Parameter Dictionary. - see ffmpegVideoSystem plugin for anexample. To make this work, two classes have been added to OGRE: ExternalTextureSource& ExternalTextureSourceManager.

ExternalTextureSource Class

The ExternalTextureSource class is the base class that Texture Source PlugIns must be de-rived from. It provides a generic framework (via StringInterface class) with a very limitedamount of functionality. The most common of parameters can be set through the Tex-turePlugInSource class interface or via the StringInterface commands contained within thisclass. While this may seem like duplication of code, it is not. By using the string commandinterface, it becomes extremely easy for derived plugins to add any new types of parametersthat it may need.

Default Command Parameters defined in ExternalTextureSource base class are:• Parameter Name: "filename" Argument Type: Ogre::String Sets a filename plugin will

read from• Parameter Name: "play mode" Argument Type: Ogre::String Sets initial play mode

to be used by the plugin - "play", "loop", "pause"• Parameter Name: "set T P S" Argument Type: Ogre::String Used to set the tech-

nique, pass, and texture unit level to apply this texture to. As an example: To set atechnique level of 1, a pass level of 2, and a texture unit level of 3, send this string "12 3".


• Parameter Name: "frames per second" Argument Type: Ogre::String Set a Framesper second update speed. (Integer Values only)

ExternalTextureSourceManager Class

ExternalTextureSourceManager is responsible for keeping track of loaded Texture SourcePlugIns. It also aids in the creation of texture source textures from scripts. It also is theinterface you should use when dealing with texture source plugins.

Note: The function prototypes shown below are mockups - param names are simplifiedto better illustrate purpose here... Steps needed to create a new texture via ExternalTex-tureSourceManager:• Obviously, the first step is to have the desired plugin included in plugin.cfg for it to be

loaded.• Set the desired PlugIn as Active via AdvancedTextureManager::getSingleton().SetCurrentPlugIn(

String Type ); – type is whatever the plugin registers as handling (e.g. "video","flash", "whatever", etc).

• Note: Consult Desired PlugIn to see what params it needs/expects. Setparams/value pairs via AdvancedTextureManager::getSingleton().getCurrentPlugIn()->setParameter( String Param, String Value );

• After required params are set, a simple call to AdvancedTextureManager::getSingleton().getCurrentPlugIn()->createDefinedTexture( sMaterialName ); will create a texture to the material namegiven.

The manager also provides a method for deleting a texture source material: Advanced-TextureManager::DestroyAdvancedTexture( String sTextureName ); The destroy methodworks by broadcasting the material name to all loaded TextureSourcePlugIns, and the Plu-gIn who actually created the material is responsible for the deletion, while other PlugInswill just ignore the request. What this means is that you do not need to worry aboutwhich PlugIn created the material, or activating the PlugIn yourself. Just call the managermethod to remove the material. Also, all texture plugins should handle cleanup when theyare shutdown.

Texture Source Material Script

As mentioned earlier, the process of defining/creating texture sources can be done withinmaterial script file. Here is an example of a material script definition - Note: This exampleis based off the ffmpegVideoSystem plugin parameters.material Example/MyVideoExample{

technique{

pass


{texture_unit{

texture_source video{

filename mymovie.mpegplay_mode playsound_mode on

}}

}}

}

Notice that the first two param/value pairs are defined in the ExternalTextureSourcebase class and that the third parameter/value pair is not defined in the base class... Thatparameter is added to the param dictionary by the ffmpegVideoPlugin... This shows thatextending the functionality with the plugins is extremely easy. Also, pay particular attentionto the line: texture source video. This line identifies that this texture unit will come from atexture source plugin. It requires one parameter that determines which texture plugin willbe used. In the example shown, the plugin requested is one that registered with "video"name.

Simplified Diagram of Process

This diagram uses ffmpegVideoPlugin as example, but all plug ins will work the same in howthey are registered/used here. Also note that TextureSource Plugins are loaded/registeredbefore scripts are parsed. This does not mean that they are initialized... Plugins are notinitialized until they are set active! This is to ensure that a rendersystem is setup beforethe plugins might make a call the rendersystem.

Chapter 7: Shadows 180

7 Shadows

Shadows are clearly an important part of rendering a believable scene - they provide a moretangible feel to the objects in the scene, and aid the viewer in understanding the spatialrelationship between objects. Unfortunately, shadows are also one of the most challengingaspects of 3D rendering, and they are still very much an active area of research. Whilst thereare many techniques to render shadows, none is perfect and they all come with advantagesand disadvantages. For this reason, Ogre provides multiple shadow implementations, withplenty of configuration settings, so you can choose which technique is most appropriate foryour scene.

Shadow implementations fall into basically 2 broad categories: Section 7.1 [Stencil Shad-ows], page 181 and Section 7.2 [Texture-based Shadows], page 185. This describes themethod by which the shape of the shadow is generated. In addition, there is more than oneway to render the shadow into the scene: Section 7.3 [Modulative Shadows], page 190, whichdarkens the scene in areas of shadow, and Section 7.4 [Additive Light Masking], page 191which by contrast builds up light contribution in areas which are not in shadow. You alsohave the option of [Integrated Texture Shadows], page 189 which gives you complete controlover texture shadow application, allowing for complex single-pass shadowing shaders. Ogresupports all these combinations.

Enabling shadows

Shadows are disabled by default, here’s how you turn them on and configure them in thegeneral sense:1. Enable a shadow technique on the SceneManager as the first thing you doing your

scene setup. It is important that this is done first because the shadow technique canalter the way meshes are loaded. Here’s an example:mSceneMgr->setShadowTechnique(SHADOWTYPE_STENCIL_ADDITIVE);

2. Create one or more lights. Note that not all light types are necessarily supported byall shadow techniques, you should check the sections about each technique to check.Note that if certain lights should not cast shadows, you can turn that off by callingsetCastShadows(false) on the light, the default is true.

3. Disable shadow casting on objects which should not cast shadows. Call setCastShad-ows(false) on objects you don’t want to cast shadows, the default for all objects is tocast shadows.

4. Configure shadow far distance. You can limit the distance at which shadows are con-sidered for performance reasons, by calling SceneManager::setShadowFarDistance.

5. Turn off the receipt of shadows on materials that should not receive them. You canturn off the receipt of shadows (note, not the casting of shadows - that is done per-object) by calling Material::setReceiveShadows or using the receive shadows materialattribute. This is useful for materials which should be considered self-illuminated forexample. Note that transparent materials are typically excluded from receiving and


casting shadows, although see the [transparency casts shadows], page 20 option forexceptions.

Opting out of shadows

By default Ogre treats all non-transparent objects as shadow casters and receivers (depend-ing on the shadow technique they may not be able to be both at once, check the docs foryour chosen technique first). You can disable shadows in various ways:

Turning off shadow casting on the lightCalling Light::setCastsShadows(false) will mean this light casts no shadows atall.

Turn off shadow receipt on a materialCalling Material::setReceiveShadows(false) will prevent any objects using thismaterial from receiving shadows.

Turn off shadow casting on individual objectsCalling MovableObject::setCastsShadows(false) will disable shadow casting forthis object.

Turn off shadows on an entire rendering queue groupCalling RenderQueueGroup::setShadowsEnabled(false) will turn off bothshadow casting and receiving on an entire rendering queue group. This isuseful because Ogre has to do light setup tasks per group in order to preservethe inter-group ordering. Ogre automatically disables shadows on a numberof groups automatically, such as RENDER QUEUE BACKGROUND,RENDER QUEUE OVERLAY, RENDER QUEUE SKIES EARLY andRENDER QUEUE SKIES LATE. If you choose to use more rendering queues(and by default, you won’t be using any more than this plus the ’standard’queue, so ignore this if you don’t know what it means!), be aware that eachone can incur a light setup cost, and you should disable shadows on theadditional ones you use if you can.

7.1 Stencil Shadows

Stencil shadows are a method by which a ’mask’ is created for the screen using a featurecalled the stencil buffer. This mask can be used to exclude areas of the screen from sub-sequent renders, and thus it can be used to either include or exclude areas in shadow.They are enabled by calling SceneManager::setShadowTechnique with a parameter of ei-ther SHADOWTYPE_STENCIL_ADDITIVE or SHADOWTYPE_STENCIL_MODULATIVE. Because thestencil can only mask areas to be either ’enabled’ or ’disabled’, stencil shadows have ’hard’edges, that is to say clear dividing lines between light and shadow - it is not possible tosoften these edges.

In order to generate the stencil, ’shadow volumes’ are rendered by extruding the silhou-ette of the shadow caster away from the light. Where these shadow volumes intersect otherobjects (or the caster, since self-shadowing is supported using this technique), the stencilis updated, allowing subsequent operations to differentiate between light and shadow. How


exactly this is used to render the shadows depends on whether Section 7.3 [ModulativeShadows], page 190 or Section 7.4 [Additive Light Masking], page 191 is being used. Ob-jects can both cast and receive stencil shadows, so self-shadowing is inbuilt.

The advantage of stencil shadows is that they can do self-shadowing simply on low-end hardware, provided you keep your poly count under control. In contrast doing self-shadowing with texture shadows requires a fairly modern machine (See Section 7.2 [Texture-based Shadows], page 185). For this reason, you’re likely to pick stencil shadows if you needan accurate shadowing solution for an application aimed at older or lower-spec machines.

The disadvantages of stencil shadows are numerous though, especially on more modernhardware. Because stencil shadows are a geometric technique, they are inherently morecostly the higher the number of polygons you use, meaning you are penalized the moredetailed you make your meshes. The fillrate cost, which comes from having to rendershadow volumes, also escalates the same way. Since more modern applications are likely touse higher polygon counts, stencil shadows can start to become a bottleneck. In addition,the visual aspects of stencil shadows are pretty primitive - your shadows will always behard-edged, and you have no possibility of doing clever things with shaders since the stencilis not available for manipulation there. Therefore, if your application is aimed at higher-end machines you should definitely consider switching to texture shadows (See Section 7.2[Texture-based Shadows], page 185).

There are a number of issues to consider which are specific to stencil shadows:

• [CPU Overhead], page 182• [Extrusion distance], page 183• [Camera far plane positioning], page 183• [Mesh edge lists], page 183• [The Silhouette Edge], page 183• [Be realistic], page 184• [Stencil Optimisations Performed By Ogre], page 184

CPU Overhead

Calculating the shadow volume for a mesh can be expensive, and it has to be done on theCPU, it is not a hardware accelerated feature. Therefore, you can find that if you overusethis feature, you can create a CPU bottleneck for your application. Ogre quite aggressivelyeliminates objects which cannot be casting shadows on the frustum, but there are limitsto how much it can do, and large, elongated shadows (e.g. representing a very low sunposition) are very difficult to cull efficiently. Try to avoid having too many shadow castersaround at once, and avoid long shadows if you can. Also, make use of the ’shadow fardistance’ parameter on the SceneManager, this can eliminate distant shadow casters fromthe shadow volume construction and save you some time, at the expense of only havingshadows for closer objects. Lastly, make use of Ogre’s Level-Of-Detail (LOD) features; youcan generate automatically calculated LODs for your meshes in code (see the Mesh API


docs) or when using the mesh tools such as OgreXmlConverter and OgreMeshUpgrader.Alternatively, you can assign your own manual LODs by providing alternative mesh files atlower detail levels. Both methods will cause the shadow volume complexity to decrease asthe object gets further away, which saves you valuable volume calculation time.

Extrusion distance

When vertex programs are not available, Ogre can only extrude shadow volumes a finitedistance from the object. If an object gets too close to a light, any finite extrusion dis-tance will be inadequate to guarantee all objects will be shadowed properly by this object.Therefore, you are advised not to let shadow casters pass too close to light sources if youcan avoid it, unless you can guarantee that your target audience will have vertex programcapable hardware (in this case, Ogre extrudes the volume to infinity using a vertex programso the problem does not occur).

When infinite extrusion is not possible, Ogre uses finite extrusion, either derived from theattenuation range of a light (in the case of a point light or spotlight), or a fixed extrusiondistance set in the application in the case of directional lights. To change the directionallight extrusion distance, use SceneManager::setShadowDirectionalLightExtrusionDistance.

Camera far plane positioning

Stencil shadow volumes rely very much on not being clipped by the far plane. When youenable stencil shadows, Ogre internally changes the far plane settings of your cameras suchthat there is no far plane - i.e. it is placed at infinity (Camera::setFarClipDistance(0)). Thisavoids artifacts caused by clipping the dark caps on shadow volumes, at the expense of a(very) small amount of depth precision.

Mesh edge lists

Stencil shadows can only be calculated when an ’edge list’ has been built for all the geometryin a mesh. The official exporters and tools automatically build this for you (or have an optionto do so), but if you create your own meshes, you must remember to build edge lists forthem before using them with stencil shadows - you can do that by using OgreMeshUpgradeor OgreXmlConverter, or by calling Mesh::buildEdgeList before you export or use the mesh.If a mesh doesn’t have edge lists, OGRE assumes that it is not supposed to cast stencilshadows.

The Silhouette Edge

Stencil shadowing is about finding a silhouette of the mesh, and projecting it away to form avolume. What this means is that there is a definite boundary on the shadow caster betweenlight and shadow; a set of edges where where the triangle on one side is facing toward thelight, and one is facing away. This produces a sharp edge around the mesh as the transitionoccurs. Provided there is little or no other light in the scene, and the mesh has smoothnormals to produce a gradual light change in its underlying shading, the silhouette edgecan be hidden - this works better the higher the tessellation of the mesh. However, if thescene includes ambient light, then the difference is far more marked. This is especially truewhen using Section 7.3 [Modulative Shadows], page 190, because the light contribution ofeach shadowed area is not taken into account by this simplified approach, and so using 2


or more lights in a scene using modulative stencil shadows is not advisable; the silhouetteedges will be very marked. Additive lights do not suffer from this as badly because eachlight is masked individually, meaning that it is only ambient light which can show up thesilhouette edges.

Be realistic

Don’t expect to be able to throw any scene using any hardware at the stencil shadowalgorithm and expect to get perfect, optimum speed results. Shadows are a complex andexpensive technique, so you should impose some reasonable limitations on your placing oflights and objects; they’re not really that restricting, but you should be aware that this isnot a complete free-for-all.

• Try to avoid letting objects pass very close (or even through) lights - it might look nicebut it’s one of the cases where artifacts can occur on machines not capable of runningvertex programs.

• Be aware that shadow volumes do not respect the ’solidity’ of the objects they passthrough, and if those objects do not themselves cast shadows (which would hide theeffect) then the result will be that you can see shadows on the other side of what shouldbe an occluding object.

• Make use of SceneManager::setShadowFarDistance to limit the number of shadow vol-umes constructed

• Make use of LOD to reduce shadow volume complexity at distance

• Avoid very long (dusk and dawn) shadows - they exacerbate other issues such as volumeclipping, fillrate, and cause many more objects at a greater distance to require volumeconstruction.

Stencil Optimisations Performed By Ogre

Despite all that, stencil shadows can look very nice (especially with Section 7.4 [AdditiveLight Masking], page 191) and can be fast if you respect the rules above. In addition, Ogrecomes pre-packed with a lot of optimisations which help to make this as quick as possible.This section is more for developers or people interested in knowing something about the’under the hood’ behaviour of Ogre.

Vertex program extrusionAs previously mentioned, Ogre performs the extrusion of shadow volumes inhardware on vertex program-capable hardware (e.g. GeForce3, Radeon 8500 orbetter). This has 2 major benefits; the obvious one being speed, but secondlythat vertex programs can extrude points to infinity, which the fixed-functionpipeline cannot, at least not without performing all calculations in software.This leads to more robust volumes, and also eliminates more than half thevolume triangles on directional lights since all points are projected to a singlepoint at infinity.


Scissor test optimisationOgre uses a scissor rectangle to limit the effect of point / spot lights whentheir range does not cover the entire viewport; that means we save fillrate whenrendering stencil volumes, especially with distant lights

Z-Pass and Z-Fail algorithmsThe Z-Fail algorithm, often attributed to John Carmack, is used in Ogre tomake sure shadows are robust when the camera passes through the shadowvolume. However, the Z-Fail algorithm is more expensive than the traditionalZ-Pass; so Ogre detects when Z-Fail is required and only uses it then, Z-Pass isused at all other times.

2-Sided stencilling and stencil wrappingOgre supports the 2-Sided stencilling / stencil wrapping extensions, which whensupported allow volumes to be rendered in a single pass instead of having todo one pass for back facing tris and another for front-facing tris. This doesn’tsave fillrate, since the same number of stencil updates are done, but it does saveprimitive setup and the overhead incurred in the driver every time a render callis made.

Aggressive shadow volume cullingOgre is pretty good at detecting which lights could be affecting the frustum, andfrom that, which objects could be casting a shadow on the frustum. This meanswe don’t waste time constructing shadow geometry we don’t need. Setting theshadow far distance is another important way you can reduce stencil shadowoverhead since it culls far away shadow volumes even if they are visible, whichis beneficial in practice since you’re most interested in shadows for close-upobjects.

7.2 Texture-based Shadows

Texture shadows involve rendering shadow casters from the point of view of the light intoa texture, which is then projected onto shadow receivers. The main advantage of textureshadows as opposed to Section 7.1 [Stencil Shadows], page 181 is that the overhead ofincreasing the geometric detail is far lower, since there is no need to perform per-trianglecalculations. Most of the work in rendering texture shadows is done by the graphics card,meaning the technique scales well when taking advantage of the latest cards, which areat present outpacing CPUs in terms of their speed of development. In addition, textureshadows are much more customisable - you can pull them into shaders to apply as youlike (particularly with [Integrated Texture Shadows], page 189, you can perform filteringto create softer shadows or perform other special effects on them. Basically, most modernengines use texture shadows as their primary shadow technique simply because they aremore powerful, and the increasing speed of GPUs is rapidly amortizing the fillrate / textureaccess costs of using them.

The main disadvantage to texture shadows is that, because they are simply a texture,they have a fixed resolution which means if stretched, the pixellation of the texture canbecome obvious. There are ways to combat this though:


Choosing a projection basisThe simplest projection is just to render the shadow casters from the lightsperspective using a regular camera setup. This can look bad though, so thereare many other projections which can help to improve the quality from themain camera’s perspective. OGRE supports pluggable projection bases via it’sShadowCameraSetup class, and comes with several existing options - Uniform(which is the simplest), Uniform Focussed (which is still a normal camera pro-jection, except that the camera is focussed into the area that the main viewingcamera is looking at), LiSPSM (Light Space Perspective Shadow Mapping -which both focusses and distorts the shadow frustum based on the main viewcamera) and Plan Optimal (which seeks to optimise the shadow fidelity for asingle receiver plane).

Filtering You can also sample the shadow texture multiple times rather than once tosoften the shadow edges and improve the appearance. Percentage Closest Fil-tering (PCF) is the most popular approach, although there are multiple variantsdepending on the number and pattern of the samples you take. Our shadowsdemo includes a 5-tap PCF example combined with depth shadow mapping.

Using a larger textureAgain as GPUs get faster and gain more memory, you can scale up to takeadvantage of this.

If you combine all 3 of these techniques you can get a very high quality shadow solution.The other issue is with point lights. Because texture shadows require a render to texture

in the direction of the light, omnidirectional lights (point lights) would require 6 rendersto totally cover all the directions shadows might be cast. For this reason, Ogre primarilysupports directional lights and spotlights for generating texture shadows; you can use pointlights but they will only work if off-camera since they are essentially turned into a spotlightshining into your camera frustum for the purposes of texture shadows.

Directional Lights

Directional lights in theory shadow the entire scene from an infinitely distant light. Now,since we only have a finite texture which will look very poor quality if stretched over theentire scene, clearly a simplification is required. Ogre places a shadow texture over the areaimmediately in front of the camera, and moves it as the camera moves (although it roundsthis movement to multiples of texels so that the slight ’swimming shadow’ effect causedby moving the texture is minimised). The range to which this shadow extends, and theoffset used to move it in front of the camera, are configurable (See [Configuring TextureShadows], page 187). At the far edge of the shadow, Ogre fades out the shadow based onother configurable parameters so that the termination of the shadow is softened.

Spotlights

Spotlights are much easier to represent as renderable shadow textures than directionallights, since they are naturally a frustum. Ogre represents spotlight directly by renderingthe shadow from the light position, in the direction of the light cone; the field-of-view of


the texture camera is adjusted based on the spotlight falloff angles. In addition, to hide thefact that the shadow texture is square and has definite edges which could show up outsidethe spotlight, Ogre uses a second texture unit when projecting the shadow onto the scenewhich fades out the shadow gradually in a projected circle around the spotlight.

Point Lights

As mentioned above, to support point lights properly would require multiple renders (either6 for a cubic render or perhaps 2 for a less precise parabolic mapping), so rather than dothat we approximate point lights as spotlights, where the configuration is changed on thefly to make the light shine from its position over the whole of the viewing frustum. This isnot an ideal setup since it means it can only really work if the point light’s position is outof view, and in addition the changing parameterisation can cause some ’swimming’ of thetexture. Generally we recommend avoiding making point lights cast texture shadows.

Shadow Casters and Shadow Receivers

To enable texture shadows, use the shadow technique SHADOWTYPE TEXTURE MODULATIVEor SHADOWTYPE TEXTURE ADDITIVE; as the name suggests this producesSection 7.3 [Modulative Shadows], page 190 or Section 7.4 [Additive Light Masking],page 191 respectively. The cheapest and simplest texture shadow techniques do notuse depth information, they merely render casters to a texture and render this ontoreceivers as plain colour - this means self-shadowing is not possible using these methods.This is the default behaviour if you use the automatic, fixed-function compatible (andthus usable on lower end hardware) texture shadow techniques. You can however useshaders-based techniques through custom shadow materials for casters and receivers toperform more complex shadow algorithms, such as depth shadow mapping which doesallow self-shadowing. OGRE comes with an example of this in its shadows demo, althoughit’s only usable on Shader Model 2 cards or better. Whilst fixed-function depth shadowmapping is available in OpenGL, it was never standardised in Direct3D so using shadersin custom caster & receiver materials is the only portable way to do it. If you use thisapproach, call SceneManager::setShadowTextureSelfShadow with a parameter of ’true’ toallow texture shadow casters to also be receivers.

If you’re not using depth shadow mapping, OGRE divides shadow casters and receivers into2 disjoint groups. Simply by turning off shadow casting on an object, you automaticallymake it a shadow receiver (although this can be disabled by setting the ’receive shadows’option to ’false’ in a material script. Similarly, if an object is set as a shadow caster, itcannot receive shadows.

Configuring Texture Shadows

There are a number of settings which will help you configure your texture-based shadowsso that they match your requirements.


bullet [Maximum number of shadow textures], page 188bullet [Shadow texture size], page 188bullet [Shadow far distance], page 188bullet [Shadow texture offset (Directional Lights)], page 189bullet [Shadow fade settings], page 189bullet [Custom shadow camera setups], page 189bullet [Integrated Texture Shadows], page 189

Maximum number of shadow textures

Shadow textures take up texture memory, and to avoid stalling the rendering pipeline Ogredoes not reuse the same shadow texture for multiple lights within the same frame. Thismeans that each light which is to cast shadows must have its own shadow texture. Inpractice, if you have a lot of lights in your scene you would not wish to incur that sort oftexture overhead.

You can adjust this manually by simply turning off shadow casting for lights you do notwish to cast shadows. In addition, you can set a maximum limit on the number of shadowtextures Ogre is allowed to use by calling SceneManager::setShadowTextureCount. Eachframe, Ogre determines the lights which could be affecting the frustum, and then allocatesthe number of shadow textures it is allowed to use to the lights on a first-come-first-servedbasis. Any additional lights will not cast shadows that frame.

Note that you can set the number of shadow textures and their size at the same time byusing the SceneManager::setShadowTextureSettings method; this is useful because both theindividual calls require the potential creation / destruction of texture resources.

Shadow texture size

The size of the textures used for rendering the shadow casters into can be altered;clearly using larger textures will give you better quality shadows, but at the expenseof greater memory usage. Changing the texture size is done by calling SceneMan-ager::setShadowTextureSize - textures are assumed to be square and you must specify atexture size that is a power of 2. Be aware that each modulative shadow texture will takesize*size*3 bytes of texture memory.

Important: if you use the GL render system your shadow texture size can only be larger(in either dimension) than the size of your primary window surface if the hardwaresupports the Frame Buffer Object (FBO) or Pixel Buffer Object (PBO) extensions. Mostmodern cards support this now, but be careful of older cards - you can check the ability ofthe hardware to manage this through ogreRoot->getRenderSystem()->getCapabilities()->hasCapability(RSC HWRENDER TO TEXTURE). If this returns false, if you create ashadow texture larger in any dimension than the primary surface, the rest of the shadowtexture will be blank.

Shadow far distance

This determines the distance at which shadows are terminated; it also determines how farinto the distance the texture shadows for directional lights are stretched - by reducing this


value, or increasing the texture size, you can improve the quality of shadows from directionallights at the expense of closer shadow termination or increased memory usage, respectively.

Shadow texture offset (Directional Lights)

As mentioned above in the directional lights section, the rendering of shadows for direc-tional lights is an approximation that allows us to use a single render to cover a largisharea with shadows. This offset parameter affects how far from the camera position thecenter of the shadow texture is offset, as a proportion of the shadow far distance. Thegreater this value, the more of the shadow texture is ’useful’ to you since it’s ahead of thecamera, but also the further you offset it, the more chance there is of accidentally seeingthe edge of the shadow texture at more extreme angles. You change this value by callingSceneManager::setShadowDirLightTextureOffset, the default is 0.6.

Shadow fade settings

Shadows fade out before the shadow far distance so that the termination of shadow is notabrupt. You can configure the start and end points of this fade by calling the SceneMan-ager::setShadowTextureFadeStart and SceneManager::setShadowTextureFadeEnd methods,both take distances as a proportion of the shadow far distance. Because of the inaccuraciescaused by using a square texture and a radial fade distance, you cannot use 1.0 as the fadeend, if you do you’ll see artifacts at the extreme edges. The default values are 0.7 and 0.9,which serve most purposes but you can change them if you like.

Texture shadows and vertex / fragment programs

When rendering shadow casters into a modulative shadow texture, Ogre turns off all tex-tures, and all lighting contributions except for ambient light, which it sets to the colour ofthe shadow ([Shadow Colour], page 191). For additive shadows, it render the casters into ablack & white texture instead. This is enough to render shadow casters for fixed-functionmaterial techniques, however where a vertex program is used Ogre doesn’t have so muchcontrol. If you use a vertex program in the first pass of your technique, then you must alsotell ogre which vertex program you want it to use when rendering the shadow caster; see[Shadows and Vertex Programs], page 93 for full details.

Custom shadow camera setups

As previously mentioned, one of the downsides of texture shadows is that the texture resolu-tion is finite, and it’s possible to get aliasing when the size of the shadow texel is larger thana screen pixel, due to the projection of the texture. In order to address this, you can spec-ify alternative projection bases by using or creating subclasses of the ShadowCameraSetupclass. The default version is called DefaultShadowCameraSetup and this sets up a simpleregular frustum for point and spotlights, and an orthographic frustum for directional lights.There is also a PlaneOptimalShadowCameraSetup class which specialises the projection toa plane, thus giving you much better definition provided your shadow receivers exist mostlyin a single plane. Other setup classes (e.g. you might create a perspective or trapezoidshadow mapping version) can be created and plugged in at runtime, either on individuallights or on the SceneManager as a whole.


Integrated Texture Shadows

Texture shadows have one major advantage over stencil shadows - the data usedto represent them can be referenced in regular shaders. Whilst the default textureshadow modes (SHADOWTYPE TEXTURE MODULATIVE and SHADOW-TYPE TEXTURE ADDITIVE) automatically render shadows for you, their disadvantageis that because they are generalised add-ons to your own materials, they tend to take morepasses of the scene to use. In addition, you don’t have a lot of control over the compositionof the shadows.

Here is where ’integrated’ texture shadows step in. Both of the texture shadow typesabove have alternative versions called SHADOWTYPE TEXTURE MODULATIVE INTEGRATEDand SHADOWTYPE TEXTURE ADDITIVE INTEGRATED, where instead of renderingthe shadows for you, it just creates the texture shadow and then expects you to use thatshadow texture as you see fit when rendering receiver objects in the scene. The downsideis that you have to take into account shadow receipt in every one of your materials if youuse this option - the upside is that you have total control over how the shadow texturesare used. The big advantage here is that you can can perform more complex shading,taking into account shadowing, than is possible using the generalised bolt-on approaches,AND you can probably write them in a smaller number of passes, since you know preciselywhat you need and can combine passes where possible. When you use one of theseshadowing approaches, the only difference between additive and modulative is the colourof the casters in the shadow texture (the shadow colour for modulative, black for additive)- the actual calculation of how the texture affects the receivers is of course up to you.No separate modulative pass will be performed, and no splitting of your materials intoambient / per-light / decal etc will occur - absolutely everything is determined by youroriginal material (which may have modulative passes or per-light iteration if you want ofcourse, but it’s not required).

You reference a shadow texture in a material which implements this approach by usingthe ’[content type], page 51 shadow’ directive in your {texture unit. It implicitly referencesa shadow texture based on the number of times you’ve used this directive in the same pass,and the light start option or light-based pass iteration, which might start the light indexhigher than 0.

7.3 Modulative Shadows

Modulative shadows work by darkening an already rendered scene with a fixed colour. First,the scene is rendered normally containing all the objects which will be shadowed, then amodulative pass is done per light, which darkens areas in shadow. Finally, objects whichdo not receive shadows are rendered.

There are 2 modulative shadow techniques; stencil-based (See Section 7.1[Stencil Shadows], page 181 : SHADOWTYPE STENCIL MODULATIVE) and


texture-based (See Section 7.2 [Texture-based Shadows], page 185 : SHADOW-TYPE TEXTURE MODULATIVE). Modulative shadows are an inaccurate lightingmodel, since they darken the areas of shadow uniformly, irrespective of the amount oflight which would have fallen on the shadow area anyway. However, they can give fairlyattractive results for a much lower overhead than more ’correct’ methods like Section 7.4[Additive Light Masking], page 191, and they also combine well with pre-baked staticlighting (such as pre-calculated lightmaps), which additive lighting does not. The mainthing to consider is that using multiple light sources can result in overly dark shadows(where shadows overlap, which intuitively looks right in fact, but it’s not physicallycorrect) and artifacts when using stencil shadows (See [The Silhouette Edge], page 183).

Shadow Colour

The colour which is used to darken the areas in shadow is set by SceneMan-ager::setShadowColour; it defaults to a dark grey (so that the underlying colour still showsthrough a bit).

Note that if you’re using texture shadows you have the additional option of using[Integrated Texture Shadows], page 189 rather than being forced to have a separate pass ofthe scene to render shadows. In this case the ’modulative’ aspect of the shadow techniquejust affects the colour of the shadow texture.

7.4 Additive Light Masking

Additive light masking is about rendering the scene many times, each time representinga single light contribution whose influence is masked out in areas of shadow. Each passis combined with (added to) the previous one such that when all the passes are complete,all the light contribution has correctly accumulated in the scene, and each light has beenprevented from affecting areas which it should not be able to because of shadow casters.This is an effective technique which results in very realistic looking lighting, but it comesat a price: more rendering passes.

As many technical papers (and game marketing) will tell you, rendering realistic lightinglike this requires multiple passes. Being a friendly sort of engine, Ogre frees you from mostof the hard work though, and will let you use the exact same material definitions whetheryou use this lighting technique or not (for the most part, see [Pass Classification and VertexPrograms], page 193). In order to do this technique, Ogre automatically categorises theSection 3.1.2 [Passes], page 24 you define in your materials into 3 types:

1. ambient Passes categorised as ’ambient’ include any base pass which is not lit by anyparticular light, i.e. it occurs even if there is no ambient light in the scene. Theambient pass always happens first, and sets up the initial depth value of the fragments,


and the ambient colour if applicable. It also includes any emissive / self illuminationcontribution. Only textures which affect ambient light (e.g. ambient occlusion maps)should be rendered in this pass.

2. diffuse/specular Passes categorised as ’diffuse/specular’ (or ’per-light’) are renderedonce per light, and each pass contributes the diffuse and specular colour from thatsingle light as reflected by the diffuse / specular terms in the pass. Areas in shadowfrom that light are masked and are thus not updated. The resulting masked colouris added to the existing colour in the scene. Again, no textures are used in this pass(except for textures used for lighting calculations such as normal maps).

3. decal Passes categorised as ’decal’ add the final texture colour to the scene, which ismodulated by the accumulated light built up from all the ambient and diffuse/specularpasses.

In practice, Section 3.1.2 [Passes], page 24 rarely fall nicely into just one of these cate-gories. For each Technique, Ogre compiles a list of ’Illumination Passes’, which are derivedfrom the user defined passes, but can be split, to ensure that the divisions between illumi-nation pass categories can be maintained. For example, if we take a very simple materialdefinition:

material TestIllumination{

technique{

pass{

ambient 0.5 0.2 0.2diffuse 1 0 0specular 1 0.8 0.8 15texture_unit{

texture grass.png}

}}

}

Ogre will split this into 3 illumination passes, which will be the equivalent of this:

material TestIlluminationSplitIllumination{

technique{

// Ambient passpass{

ambient 0.5 0.2 0.2diffuse 0 0 0specular 0 0 0

}


// Diffuse / specular passpass{

scene_blend additeration once_per_lightdiffuse 1 0 0specular 1 0.8 0.8 15

}

// Decal passpass{

scene_blend modulatelighting offtexture_unit{

texture grass.png}

}}

}

So as you can see, even a simple material requires a minimum of 3 passes when usingthis shadow technique, and in fact it requires (num lights + 2) passes in the general sense.You can use more passes in your original material and Ogre will cope with that too, butbe aware that each pass may turn into multiple ones if it uses more than one type of lightcontribution (ambient vs diffuse/specular) and / or has texture units. The main nice thingis that you get the full multipass lighting behaviour even if you don’t define your materialsin terms of it, meaning that your material definitions can remain the same no matter whatlighting approach you decide to use.

Manually Categorising Illumination Passes

Alternatively, if you want more direct control over the categorisation of your passes, youcan use the [illumination stage], page 35 option in your pass to explicitly assign a passunchanged to an illumination stage. This way you can make sure you know precisely howyour material will be rendered under additive lighting conditions.

Pass Classification and Vertex Programs

Ogre is pretty good at classifying and splitting your passes to ensure that the multipassrendering approach required by additive lighting works correctly without you having tochange your material definitions. However, there is one exception; when you use vertexprograms, the normal lighting attributes ambient, diffuse, specular etc are not used, becauseall of that is determined by the vertex program. Ogre has no way of knowing what you’redoing inside that vertex program, so you have to tell it.


In practice this is very easy. Even though your vertex program could be doing a lotof complex, highly customised processing, it can still be classified into one of the 3 typeslisted above. All you need to do to tell Ogre what you’re doing is to use the pass attributesambient, diffuse, specular and self illumination, just as if you were not using a vertexprogram. Sure, these attributes do nothing (as far as rendering is concerned) when you’reusing vertex programs, but it’s the easiest way to indicate to Ogre which light componentsyou’re using in your vertex program. Ogre will then classify and potentially split yourprogrammable pass based on this information - it will leave the vertex program as-is (sothat any split passes will respect any vertex modification that is being done).

Note that when classifying a diffuse/specular programmable pass, Ogre checks to seewhether you have indicated the pass can be run once per light (iteration once per light).If so, the pass is left intact, including it’s vertex and fragment programs. However, if thisattribute is not included in the pass, Ogre tries to split off the per-light part, and in doingso it will disable the fragment program, since in the absence of the ’iteration once per light’attribute it can only assume that the fragment program is performing decal work and hencemust not be used per light.

So clearly, when you use additive light masking as a shadow technique, you need to makesure that programmable passes you use are properly set up so that they can be classifiedcorrectly. However, also note that the changes you have to make to ensure the classificationis correct does not affect the way the material renders when you choose not to use additivelighting, so the principle that you should be able to use the same material definitions forall lighting scenarios still holds. Here is an example of a programmable material which willbe classified correctly by the illumination pass classifier:// Per-pixel normal mapping Any number of lights, diffuse and specularmaterial Examples/BumpMapping/MultiLightSpecular{

technique{

// Base ambient passpass{

// ambient only, not needed for rendering, but as information// to lighting pass categorisation routineambient 1 1 1diffuse 0 0 0specular 0 0 0 0// Really basic vertex programvertex_program_ref Ogre/BasicVertexPrograms/AmbientOneTexture{


param_named_auto worldViewProj worldviewproj_matrixparam_named_auto ambient ambient_light_colour

}

}// Now do the lighting pass// NB we don’t do decal texture here because this is repeated per lightpass{

// set ambient off, not needed for rendering, but as information// to lighting pass categorisation routineambient 0 0 0// do this for each lightiteration once_per_light

scene_blend add

// Vertex program referencevertex_program_ref Examples/BumpMapVPSpecular{

param_named_auto lightPosition light_position_object_space 0param_named_auto eyePosition camera_position_object_spaceparam_named_auto worldViewProj worldviewproj_matrix

}

// Fragment programfragment_program_ref Examples/BumpMapFPSpecular{

param_named_auto lightDiffuse light_diffuse_colour 0param_named_auto lightSpecular light_specular_colour 0

}

// Base bump maptexture_unit{

texture NMBumpsOut.pngcolour_op replace

}// Normalisation cube maptexture_unit{

cubic_texture nm.png combinedUVWtex_coord_set 1tex_address_mode clamp

}// Normalisation cube map #2


texture_unit{

cubic_texture nm.png combinedUVWtex_coord_set 1tex_address_mode clamp

}}

// Decal passpass{

lighting off// Really basic vertex programvertex_program_ref Ogre/BasicVertexPrograms/AmbientOneTexture{

param_named_auto worldViewProj worldviewproj_matrixparam_named ambient float4 1 1 1 1

}scene_blend dest_colour zerotexture_unit{

texture RustedMetal.jpg}

}}

}

Note that if you’re using texture shadows you have the additional option of using[Integrated Texture Shadows], page 189 rather than being forced to use this explicit se-quence - allowing you to compress the number of passes into a much smaller number at theexpense of defining an upper number of shadow casting lights. In this case the ’additive’aspect of the shadow technique just affects the colour of the shadow texture and it’s up toyou to combine the shadow textures in your receivers however you like.

Static Lighting

Despite their power, additive lighting techniques have an additional limitation; they do notcombine well with pre-calculated static lighting in the scene. This is because they are basedon the principle that shadow is an absence of light, but since static lighting in the scenealready includes areas of light and shadow, additive lighting cannot remove light to createnew shadows. Therefore, if you use the additive lighting technique you must either useit exclusively as your lighting solution (and you can combine it with per-pixel lighting tocreate a very impressive dynamic lighting solution), or you must use [Integrated TextureShadows], page 189 to combine the static lighting according to your chosen approach.

Chapter 8: Animation 197

8 Animation

OGRE supports a pretty flexible animation system that allows you to script animation forseveral different purposes:

Section 8.1 [Skeletal Animation], page 197Mesh animation using a skeletal structure to determine how the mesh deforms.

Section 8.3 [Vertex Animation], page 198Mesh animation using snapshots of vertex data to determine how the shape ofthe mesh changes.

Section 8.4 [SceneNode Animation], page 203Animating SceneNodes automatically to create effects like camera sweeps, ob-jects following predefined paths, etc.

Section 8.5 [Numeric Value Animation], page 203Using OGRE’s extensible class structure to animate any value.

8.1 Skeletal Animation

Skeletal animation is a process of animating a mesh by moving a set of hierarchical boneswithin the mesh, which in turn moves the vertices of the model according to the boneassignments stored in each vertex. An alternative term for this approach is ’skinning’.The usual way of creating these animations is with a modelling tool such as SoftimageXSI, Milkshape 3D, Blender, 3D Studio or Maya among others. OGRE provides exportersto allow you to get the data out of these modellers and into the engine See Section 4.1[Exporters], page 158.

There are many grades of skeletal animation, and not all engines (or modellers for thatmatter) support all of them. OGRE supports the following features:• Each mesh can be linked to a single skeleton• Unlimited bones per skeleton• Hierarchical forward-kinematics on bones• Multiple named animations per skeleton (e.g. ’Walk’, ’Run’, ’Jump’, ’Shoot’ etc)• Unlimited keyframes per animation• Linear or spline-based interpolation between keyframes• A vertex can be assigned to multiple bones and assigned weightings for smoother skin-

ning• Multiple animations can be applied to a mesh at the same time, again with a blend

weighting

Skeletons and the animations which go with them are held in .skeleton files, which are


produced by the OGRE exporters. These files are loaded automatically when you create anEntity based on a Mesh which is linked to the skeleton in question. You then use Section 8.2[Animation State], page 198 to set the use of animation on the entity in question.

Skeletal animation can be performed in software, or implemented in shaders (hardwareskinning). Clearly the latter is preferable, since it takes some of the work away from theCPU and gives it to the graphics card, and also means that the vertex data does not needto be re-uploaded every frame. This is especially important for large, detailed models. Youshould try to use hardware skinning wherever possible; this basically means assigning a ma-terial which has a vertex program powered technique. See 〈undefined〉 [Skeletal Animationin Vertex Programs], page 〈undefined〉 for more details. Skeletal animation can be com-bined with vertex animation, See Section 8.3.3 [Combining Skeletal and Vertex Animation],page 202.

8.2 Animation State

When an entity containing animation of any type is created, it is given an ’animation state’object per animation to allow you to specify the animation state of that single entity (youcan animate multiple entities using the same animation definitions, OGRE sorts the reuseout internally).

You can retrieve a pointer to the AnimationState object by calling En-tity::getAnimationState. You can then call methods on this returned object to updatethe animation, probably in the frameStarted event. Each AnimationState needs to beenabled using the setEnabled method before the animation it refers to will take effect,and you can set both the weight and the time position (where appropriate) to affect theapplication of the animation using correlating methods. AnimationState also has a verysimple method ’addTime’ which allows you to alter the animation position incrementally,and it will automatically loop for you. addTime can take positive or negative values (soyou can reverse the animation if you want).

8.3 Vertex Animation

Vertex animation is about using information about the movement of vertices directly toanimate the mesh. Each track in a vertex animation targets a single VertexData instance.Vertex animation is stored inside the .mesh file since it is tightly linked to the vertexstructure of the mesh.

There are actually two subtypes of vertex animation, for reasons which will be discussedin a moment.

Section 8.3.1 [Morph Animation], page 201Morph animation is a very simple technique which interpolates mesh snapshotsalong a keyframe timeline. Morph animation has a direct correlation to old-school character animation techniques used before skeletal animation was widelyused.


Section 8.3.2 [Pose Animation], page 201Pose animation is about blending multiple discrete poses, expressed as offsetsto the base vertex data, with different weights to provide a final result. Poseanimation’s most obvious use is facial animation.

Why two subtypes?

So, why two subtypes of vertex animation? Couldn’t both be implemented using the samesystem? The short answer is yes; in fact you can implement both types using pose animation.But for very good reasons we decided to allow morph animation to be specified separatelysince the subset of features that it uses is both easier to define and has lower requirementson hardware shaders, if animation is implemented through them. If you don’t care aboutthe reasons why these are implemented differently, you can skip to the next part.

Morph animation is a simple approach where we have a whole series of snapshots ofvertex data which must be interpolated, e.g. a running animation implemented as morphtargets. Because this is based on simple snapshots, it’s quite fast to use when animating anentire mesh because it’s a simple linear change between keyframes. However, this simplisticapproach does not support blending between multiple morph animations. If you needanimation blending, you are advised to use skeletal animation for full-mesh animation, andpose animation for animation of subsets of meshes or where skeletal animation doesn’t fit -for example facial animation. For animating in a vertex shader, morph animation is quitesimple and just requires the 2 vertex buffers (one the original position buffer) of absoluteposition data, and an interpolation factor. Each track in a morph animation refrences aunique set of vertex data.

Pose animation is more complex. Like morph animation each track references a singleunique set of vertex data, but unlike morph animation, each keyframe references 1 or more’poses’, each with an influence level. A pose is a series of offsets to the base vertex data,and may be sparse - i.e. it may not reference every vertex. Because they’re offsets, theycan be blended - both within a track and between animations. This set of features is verywell suited to facial animation.

For example, let’s say you modelled a face (one set of vertex data), and defined a set ofposes which represented the various phonetic positions of the face. You could then definean animation called ’SayHello’, containing a single track which referenced the face vertexdata, and which included a series of keyframes, each of which referenced one or more of thefacial positions at different influence levels - the combination of which over time made theface form the shapes required to say the word ’hello’. Since the poses are only stored once,but can be referenced may times in many animations, this is a very powerful way to buildup a speech system.


The downside of pose animation is that it can be more difficult to set up, requiringposes to be separately defined and then referenced in the keyframes. Also, since it usesmore buffers (one for the base data, and one for each active pose), if you’re animating inhardware using vertex shaders you need to keep an eye on how many poses you’re blendingat once. You define a maximum supported number in your vertex program definition,via the includes pose animation material script entry, See 〈undefined〉 [Pose Animation inVertex Programs], page 〈undefined〉.

So, by partitioning the vertex animation approaches into 2, we keep the simple morphtechnique easy to use, whilst still allowing all the powerful techniques to be used. Notethat morph animation cannot be blended with other types of vertex animation on the samevertex data (pose animation or other morph animation); pose animation can be blendedwith other pose animation though, and both types can be combined with skeletal animation.This combination limitation applies per set of vertex data though, not globally across themesh (see below). Also note that all morph animation can be expressed (in a more complexfashion) as pose animation, but not vice versa.

Subtype applies per track

It’s important to note that the subtype in question is held at a track level, not at theanimation or mesh level. Since tracks map onto VertexData instances, this means that ifyour mesh is split into SubMeshes, each with their own dedicated geometry, you can haveone SubMesh animated using pose animation, and others animated with morph animation(or not vertex animated at all).

For example, a common set-up for a complex character which needs both skeletal andfacial animation might be to split the head into a separate SubMesh with its own geometry,then apply skeletal animation to both submeshes, and pose animation to just the head.

To see how to apply vertex animation, See Section 8.2 [Animation State], page 198.

Vertex buffer arrangements

When using vertex animation in software, vertex buffers need to be arranged such thatvertex positions reside in their own hardware buffer. This is to avoid having to upload allthe other vertex data when updating, which would quickly saturate the GPU bus. Whenusing the OGRE .mesh format and the tools / exporters that go with it, OGRE organisesthis for you automatically. But if you create buffers yourself, you need to be aware of thelayout arrangements.

To do this, you have a set of helper functions in Ogre::Mesh. See API Reference entries forOgre::VertexData::reorganiseBuffers() and Ogre::VertexDeclaration::getAutoOrganisedDeclaration().The latter will turn a vertex declaration into one which is recommended for the usageyou’ve indicated, and the former will reorganise the contents of a set of buffers to conformto that layout.


8.3.1 Morph Animation

Morph animation works by storing snapshots of the absolute vertex positions in eachkeyframe, and interpolating between them. Morph animation is mainly useful for ani-mating objects which could not be adequately handled using skeletal animation; this ismostly objects that have to radically change structure and shape as part of the animationsuch that a skeletal structure isn’t appropriate.

Because absolute positions are used, it is not possible to blend more than one morphanimation on the same vertex data; you should use skeletal animation if you want to includeanimation blending since it is much more efficient. If you activate more than one animationwhich includes morph tracks for the same vertex data, only the last one will actually takeeffect. This also means that the ’weight’ option on the animation state is not used formorph animation.

Morph animation can be combined with skeletal animation if required See Section 8.3.3[Combining Skeletal and Vertex Animation], page 202. Morph animation can also be im-plemented in hardware using vertex shaders, See 〈undefined〉 [Morph Animation in VertexPrograms], page 〈undefined〉.

8.3.2 Pose Animation

Pose animation allows you to blend together potentially multiple vertex poses at differentinfluence levels into final vertex state. A common use for this is facial animation, whereeach facial expression is placed in a separate animation, and influences used to either blendfrom one expression to another, or to combine full expressions if each pose only affects partof the face.

In order to do this, pose animation uses a set of reference poses defined in the mesh,expressed as offsets to the original vertex data. It does not require that every vertex hasan offset - those that don’t are left alone. When blending in software these vertices arecompletely skipped - when blending in hardware (which requires a vertex entry for everyvertex), zero offsets for vertices which are not mentioned are automatically created for you.

Once you’ve defined the poses, you can refer to them in animations. Each pose animationtrack refers to a single set of geometry (either the shared geometry of the mesh, or dedicatedgeometry on a submesh), and each keyframe in the track can refer to one or more poses,each with its own influence level. The weight applied to the entire animation scales theseinfluence levels too. You can define many keyframes which cause the blend of poses tochange over time. The absence of a pose reference in a keyframe when it is present in aneighbouring one causes it to be treated as an influence of 0 for interpolation.


You should be careful how many poses you apply at once. When performing poseanimation in hardware (See 〈undefined〉 [Pose Animation in Vertex Programs], page 〈unde-fined〉), every active pose requires another vertex buffer to be added to the shader, and inwhen animating in software it will also take longer the more active poses you have. Bear inmind that if you have 2 poses in one keyframe, and a different 2 in the next, that actuallymeans there are 4 active keyframes when interpolating between them.

You can combine pose animation with skeletal animation, See Section 8.3.3 [Combin-ing Skeletal and Vertex Animation], page 202, and you can also hardware accelerate theapplication of the blend with a vertex shader, See 〈undefined〉 [Pose Animation in VertexPrograms], page 〈undefined〉.

8.3.3 Combining Skeletal and Vertex Animation

Skeletal animation and vertex animation (of either subtype) can both be enabled on thesame entity at the same time (See Section 8.2 [Animation State], page 198). The effect of thisis that vertex animation is applied first to the base mesh, then skeletal animation is appliedto the result. This allows you, for example, to facially animate a character using pose vertexanimation, whilst performing the main movement animation using skeletal animation.

Combining the two is, from a user perspective, as simple as just enabling both animationsat the same time. When it comes to using this feature efficiently though, there are a fewpoints to bear in mind:

bullet [Combined Hardware Skinning], page 202bullet [Submesh Splits], page 203

Combined Hardware Skinning

For complex characters it is a very good idea to implement hardware skinning by includinga technique in your materials which has a vertex program which can perform the kindsof animation you are using in hardware. See 〈undefined〉 [Skeletal Animation in VertexPrograms], page 〈undefined〉, 〈undefined〉 [Morph Animation in Vertex Programs], page 〈un-defined〉, 〈undefined〉 [Pose Animation in Vertex Programs], page 〈undefined〉.

When combining animation types, your vertex programs must support both types ofanimation that the combined mesh needs, otherwise hardware skinning will be disabled.You should implement the animation in the same way that OGRE does, ie perform vertexanimation first, then apply skeletal animation to the result of that. Remember that theimplementation of morph animation passes 2 absolute snapshot buffers of the from & tokeyframes, along with a single parametric, which you have to linearly interpolate, whilstpose animation passes the base vertex data plus ’n’ pose offset buffers, and ’n’ parametricweight values.


Submesh Splits

If you only need to combine vertex and skeletal animation for a small part of your mesh,e.g. the face, you could split your mesh into 2 parts, one which needs the combination andone which does not, to reduce the calculation overhead. Note that it will also reduce vertexbuffer usage since vertex keyframe / pose buffers will also be smaller. Note that if you usehardware skinning you should then implement 2 separate vertex programs, one which doesonly skeletal animation, and the other which does skeletal and vertex animation.

8.4 SceneNode Animation

SceneNode animation is created from the SceneManager in order to animate the movementof SceneNodes, to make any attached objects move around automatically. You can see thisperforming a camera swoop in Demo CameraTrack, or controlling how the fish move aroundin the pond in Demo Fresnel.

At it’s heart, scene node animation is mostly the same code which animates the under-lying skeleton in skeletal animation. After creating the main Animation using SceneMan-ager::createAnimation you can create a NodeAnimationTrack per SceneNode that you wantto animate, and create keyframes which control its position, orientation and scale which canbe interpolated linearly or via splines. You use Section 8.2 [Animation State], page 198 in thesame way as you do for skeletal/vertex animation, except you obtain the state from Scene-Manager instead of from an individual Entity.Animations are applied automatically everyframe, or the state can be applied manually in advance using the applySceneAnimations()method on SceneManager. See the API reference for full details of the interface for config-uring scene animations.

8.5 Numeric Value Animation

Apart from the specific animation types which may well comprise the most common uses ofthe animation framework, you can also use animations to alter any value which is exposedvia the [AnimableObject], page 203 interface.

AnimableObject

AnimableObject is an abstract interface that any class can extend in order to provide accessto a number of [AnimableValue], page 204s. It holds a ’dictionary’ of the available animableproperties which can be enumerated via the getAnimableValueNames method, and whenits createAnimableValue method is called, it returns a reference to a value object whichforms a bridge between the generic animation interfaces, and the underlying specific object


property.

One example of this is the Light class. It extends AnimableObject and provides Ani-mableValues for properties such as "diffuseColour" and "attenuation". Animation trackscan be created for these values and thus properties of the light can be scripted to change.Other objects, including your custom objects, can extend this interface in the same way toprovide animation support to their properties.

AnimableValue

When implementing custom animable properties, you have to also implement a numberof methods on the AnimableValue interface - basically anything which has been markedas unimplemented. These are not pure virtual methods simply because you only have toimplement the methods required for the type of value you’re animating. Again, see theexamples in Light to see how this is done.

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