GAM666 – Introduction To Game Programming

●DirectX is implemented as a collection of COM objects●To use a DirectX program, the user must have the correct (or later) version of DirectX installed (e.g. by doing Windows Update)●To program a DirectX program, the programmer must have the correct (or later) version of the DirectX SDK installed (from MSDN) in addition to the compiler

DirectX Programming Introduction

GAM666 – Introduction To Game Programming

●COM (Component Object Model) is one of Microsoft's ways of making objects at the operating system level [the other way is .NET]●COM builds on DLL (dynamically linked library) technology, which is a way to store precompiled functions for linking at runtime rather than compile time●COM objects can be accessed from any language supporting COM

COM Overview

GAM666 – Introduction To Game Programming

●Every COM object exposes one or more Interfaces (collection of methods to control the object)●Usually, when a new version of a COM object is released, the old interfaces are retained, and new features are implemented by creating new interfaces●This allows the object to be upgraded while still allowing programs that use the older versions to run correctly (assuming the new version doesn't break the old interfaces)

COM Overview

GAM666 – Introduction To Game Programming

Every COM interface implements at least the following three methods:●QueryInterface() – allows you to get any of the other interfaces, using the interface's ID●Release() – tells COM that you are finished using this instance of the interface so that it can be removed from memory if nothing else is using it (like C++ delete)●AddRef() – tells COM that you have just made a copy of the interface instance (which will later be Released)

COM Overview

GAM666 – Introduction To Game Programming

●Every COM object has an interface IUnknown with the three required methods [QueryInterface(), Release() and AddRef()]●This allows the programmer a predictable way to get any interface the object has (presuming the programmer knows the interface ID), in case a specialized function to obtain the interface doesn't exist

COM Overview

GAM666 – Introduction To Game Programming

Libraries (such as parts of the DirectX SDK) often have functions to instantiate desired interfaces. Alternately:●CoInitialize() can be used to initialize the generic COM access library●Then, CoCreateInstance() can be used to instantiate a particular interface of a particular COM object●If CoInitialize() is used, then CoUninitialize() must be called before the program ends

COM Overview

GAM666 – Introduction To Game Programming

●When a COM object is installed on a computer, GUIDs (Globally Unique Ids) for the object (CLSID) and its interfaces (IID) are stored in the system registry●A GUID (aka UUID – Universally Unique ID) is a 128-bit number●There are utilities to create a GUID that will [probably, to a high degree of certainty] be unique●GUIDs are used to identify much of the hardware and software installed on your PC

COM Overview

GAM666 – Introduction To Game Programming

●DirectX 7 still often used for 2D games●DirectDraw (2D graphics) was rolled into DirectX Graphics (mostly 3D graphics) starting with DirectX 8 to encourage developers to move to 3D●DirectX 7 uses some techniques that were simplified starting with DirectX 8 but which you should be prepared to encounter if maintaining legacy code

DirectX 7 Overview

GAM666 – Introduction To Game Programming

●Sample1 shows how to create a DirectDraw7 object and query it for available resolutions●The user is presented with a choice of resolutions, after which the screen resolution is changed●Technique of querying the DD7 object is a typical Windows “enumeration”, where the logic for handling one possibility is coded in a function whose address is given to Windows, and which Windows calls as many times as necesary

DirectX 7 Overview