3D Graphics Rendering and Terrain ModelingTechnology and Historical Overview

By Ricardo Veguilla

Overview

Introduction to 3D Computer Graphics

OpenGL SGI vs Linux 3D Animation Terrain Modeler: Project Status

Introduction to 3d Computer Graphics 3D computer graphics is the

science, study, and method of projecting a mathematical representation of 3D objects onto a 2D image using visual tricks such as perspective and shading to simulate the eye's perception of those objects.

3D Graphics and Physics

3D graphic software is largely based on simulating physical interactions.

Generally: Space relations. Light interactions.

In particular cases: Material properties. Object Movement.

Goals of 3D computers graphics Practical goal:

Visualization - to generate images (usually of recognizable subjects) that are useful in some way.

Ideal goal: Photorealism - to produce

images indistinguishable from photographs.

Components of a 3D Graphic System 3D Modeling:

A way to describe the 3D world or scene, which is composed of mathematical representations of 3D objects called models.

3D Rendering: A mechanism responsible for

producing a 2D image from 3D models.

3D Modeling

Simple 3D objects can be modeled using mathematical equations operating in the 3-dimensional Cartesian coordinate system.

Example:

the equation x2 + y2 + z2 = r2

is a model of a perfect sphere with radius r.

Modeling considerations

Pure mathematical equations to represent 3D objects requires a great deal of computing power

Impractical for real-time applications such as games or interactive simulations.

Alternatives: Polygon Models Modeling objects by sampling only

certain points on the object, retaining no data about the curvature in between

More efficient, but less detailed.

Alternatives: Texture Mapping Technique used to

add surface color detail without increasing the complexity of a model.

An image is mapped to the surface of a model.

From 3D models to 2D images A 3D world or scene is composed

of collection of 3d models Three different coordinates

systems (or spaces) are defined for different model related operations:Object SpaceWorld SpaceScreen Space

Object Space

The coordinate system in which a specific 3D object is defined.

Each object usually have its own object space with the origin at the object's center

The object center is the point about which the object is moved and rotated.

World Space

World space is the coordinate system of the 3D world to be rendered.

The position and orientation of all the models are defined relative to the center of the world space.

The position and orientation of the virtual camera is also defined relative to the world space.

Screen Space

2D space that represents the boundaries of the image to be produced.

Many optimization techniques are performed on screen space.

Mathematics of 3D graphics

3D operations like translation, rotation and scaling are performed using matrices and lineal algebra.

Each operation is performed by multiplying the 3D vertices by a specific transformation matrix.

3D Rendering

The process of taking the mathematical model of the world and producing the output image.

The core of the rendering process involves projecting the 3D models onto a 2D image plane.

Types of Rendering Algorithms Two general approaches:

Pixel-oriented rendering: Ray tracers

Polygon-oriented rendering: Scan-line renderers

Ray tracers

Operates by tracing theoretical light rays as they intersect objects in the scene and the projection plane.

Ray tracer limitations

Processor intensive. A full ray tracer is impractical for real-time applications.

Does not take into account inter-reflections of diffuse light, resulting in hard shadows.

Radiosity

Technique that models the inter-reflections of diffuse light between surfaces of the world or environment.

Produces more photorealistic illumination and shadows.

Scan-line renderers

Operate on an object-by-object basis, directly drawing each polygon to the screen.

Requires all objects – including those modeled with continuous curvature – to be tessellated into polygons.

Polygons are eventually tessellated into pixels.

Illumination for scan-line renderers Lighting and shading is

calculated using the normal vector.

The color is linearly interpolated across the polygon surface.

Common shading techniques scan-line rendererFlat shading

Gouraud Shading

Phong Shading

Flat Shading

The color of the polygon is calculated at the center of the polygon by using the normal vector.

The complete polygon surface is uniformly lighted.

Gouraud Shading

A normal vector is calculated at each vertex.

Color is calculated for each vertex and interpolated across the polygon

Phong Shading

The normal vectors are interpolated across the surface of the polygon

The color of each point within the polygon is calculated from its corresponding normal vector

Polygon shading techniques compared

Viewing frustum

Segment of the 3D world to be rendered

Objects outside the viewing volume are ignored.

Hidden surface determination Not all objects inside the viewing

frustum are always visible from the point of view of the camera.

Not all polygons of a particular object are visible from the point of view of the camera.

Common Techniques Painters Algorithm Z-Buffering

Painter’s Algorithm

Polygon-oriented. All the polygons are sorted by

their depth and then displayed in this order.

Z-Buffering Pixel-oriented. When multiple objects

overlap (from the point of view of the camera) on a particular pixel, only the value of the pixel closest to the camera is used.

Implemented by saving the depth value of each displayed pixel in a buffer, and comparing the depth of each new overlapping pixel against the value in the buffer.

Perspective Projection

Projects the 3D world to a 2D image

The Open Graphics Language

OpenGL – The Open Graphics Language De facto Application

Programming Interface (API) for cross-platform development of 3D graphics applications.

Implementations available for all major Operating Systems and hardware platforms.

Support for hardware accelerated 3D rendering.

Scalable, high-level, easy to use, well documented.

History of OpenGL

Originally released by SGI in the early 90s.

Descendant of IRIX GL. Previous 3D graphics APIs were

generally platform dependant. Born out of market pressure for a

cross-platform 3D API during the late 80s.

OpenGL - Code Example

How to define a triangle:

glBegin (GL_TRIANGLES);

glVertex (0,0,0);

glVertex (1,1,0);

glVertex (2,0,0);

glEnd ();

Development with OpenGL

OpenGL API designed only for drawing images.

Auxiliary visual toolkits are required for developing OpenGL applications for modern windowed desktop environments.

Potential options: GLUT, SDL, GTK+

Potential Auxiliary Toolkits

GLUT: Specifically designed for developing OpenGL demo applications.

SDL (Simple DirectMedia Layer): Library for multimedia and game development.

GTK+: General purpose toolkit for creating graphical user interfaces with OpenGL extensions available.

SGI vs Linux

VS

SGI vs Linux

Linux is quickly becoming the preferred OS for OpenGL and 3D computer graphics development.

Today Linux dominates one of SGI’s most controlled market: Movie Special Effects.

Why?

SGI and Hollywood

Special effects production pipeline involves:

The graphic workstation – Used by the artists to create the models and textures used in the visual effects sequence.

The render-farm – A computer cluster dedicated for rendering the images or animations that form the visual effect sequence.

SGI’s Market dominance

SGI dominated the market of 3D graphics solutions during the 80s and 90s.

SGI hardware provided excellent performance for rendering calculations combined with a fast video subsystem.

The computer special effects market was locked-in to SGI’s hardware.

Most of the 3D rendering software was developed for IRIX (SGI’s UNIX OS).

SGI economics disadvantages SGI’s workstations are

expensive.

Historically FX houses purchased large amount of SGIs, which were amortized over several movies (usually 5 years).

The rise of Lintel (Linux+Intel)Causes:

The development of Linux (an open source UNIX clone for the PC) during the 90s.

The continuous performance increase of the Intel CPUs.

The development of consumer-level 3D acceleration hardware for the PC driven by the growing video game market.

Why the switch to Lintel?

Lintel platform provides a higher cost/performance ratio.

Linux is a POSIX complaint UNIX clone, porting the software from IRIX is trivial.

Linux is open-source and runs in multiple-architectures which greatly limits the possibility of vendor lock-in.

Lintel economic benefits

Using Lintel, a large portion of the hardware costs can be recouped with every movie.

Buying a new render-farm for each new movie is economically viable.

Not just for the render-farm

Initially Linux was used for render-farm.

Now it is used for the graphic workstation as well.

It is even displacing Apple computers as the standard platform for video/film editing and compositing.

Results?

Movies created using Lintel: Titanic Star Wars Prequel Trilogy The Harry Potter Movies The Lord of the Rings Trilogy Shrek and Shrek 2 Practically every movie involving

special-effects made after the year 2000

Lintel on other 3D graphics areas. The Lintel cost/performance also

benefits the academic/scientific applications of 3D computer graphics.

Heavily used in automotive and aeronautics industries for solid modeling and simulations.

3D Animation

Luxo Jr.

The first film produced by Pixar in 1986.

It demonstrates the use of ray tracing to simulate the shifting light and shadow given by the animated lamps as well as simple surface textures.

It was the first CGI film to be nominated for an Academy Award.

Luxo Jr. Returns

16 years after the debut of Luxo Jr., Steve Jobs demonstrated the same animation running in real-time on a Apple G5 computer with an Nvidia Geforce 3 GPU (Graphics Processor Unit).

On 1985 - Rendering each frame of the original animation took 55 hours of processing on a Cray Supercomputer

On 2001 – Rendering each frame took 1/30 of a second on a personal computer

Terrain ModelerProject Status

Previously implemented features

Application developed in C and tested exclusively on SGI.

Terrain image loading tested with a 201x201 Matlab generated input file.

Terrain Modeling with OpenGL using points or unshaded polygons.

Fixed camera. Terrain rotation and scaling. Limited option for Level-of-detail

(LOD) rendering.

Newly Implemented Features Support for Autotools for cross-

platform development (currently tested on SGI and Linux).

Code modularization and refactoring.

Full virtual camera. Memory Manager subsystem for

monitoring memory utilization. Preliminary Lighting support. Preliminary support for rendering

multiple terrains.

Future Improvements

Full windowed application. Support for screen captures. Support for Land-marking (3D

bookmarks) Support for animation scripting

and recording. Support for simultaneous

rendering of multiple terrains.

Future Improvements (Cont.) Restructure code to accommodate

three module abstraction layers: IO Layer – Modules for reading and

writing terrain files of different formats. Sampling Layer – Modules implementing

different LOD algorithms with user-selected sampling value.

Rendering Layer – Modules for rendering the terrain using different OpenGL primitives, rendering attributes and vendor-optimized code paths.

Long-term Porting the project to Jogl: Java

OpenGL

http://java.sun.com/products/jfc/tsc/articles/jcanyon/

References: Wikipidia – The Free Encyclopedia

http://www.wikipedia.org/ OpenGL - The Industry Standard for High

Performance Graphics http://www.opengl.org/

Google Image Search http://images.google.com

Overview of 3D Interactive Graphics http://www.siggraph.org/project-grants/com97/

com97-tut.html Linux Journal - Industry of Change: Linux

Storms Hollywood http://www.linuxjournal.com/article/5472

JCanyon - Grand Canyon Demo http://java.sun.com/products/jfc/tsc/articles/jcanyo

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