GAM666 – Introduction To Game Programming DirectX Programming Introduction ● 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 GAM666 – Introduction To Game Programming COM Overview ● 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 GAM666 – Introduction To Game Programming COM Overview ● 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) GAM666 – Introduction To Game Programming COM Overview 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) GAM666 – Introduction To Game Programming COM Overview ● 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 GAM666 – Introduction To Game Programming COM Overview 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 GAM666 – Introduction To Game Programming COM Overview ● 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 GAM666 – Introduction To Game Programming DirectX 7 Overview ● 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 GAM666 – Introduction To Game Programming DirectX 7 Overview ● 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.