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DirectX

CIS 487/587

Bruce R. Maxim

UM-Dearborn

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DirectX and Win32

• Win32 Application– GDI

• Windows Device Driver Interface

– DirectX• DirectX Graphics (DirectDraw/Direct3D)• DirectX Audio (DirectSound/DirectSound3D/DirectMusic)• DirectInput• DirectPlay• DirectSetup• DirectShow

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DirectX

• Contains a run-time library consisting of several .dll’s that you may distribute with your application

• There are several .lib and .h files that make-up the development library

• You need to be sure that you know where these files are housed

• DirectX is backward compatible

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COM

• COM allows DirectX to work with multiple programming languages

• COM objects can be shipped with an application as .dll’s

• COM object provide interfaces to hardware objects

• COM objects are loaded dynamically• You can add functionality to an installed

application simply by updating the COM object

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DCOM

• An advanced version of COM

• Allows applications to access DCOM objects on networked machines

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DirectX ArchitectureWin32 App

Win GDI

Win DDI

HW Audio, Video, Input, Storage, …

DirectX

HEL: HW Emulation Layer

HAL: HW Abstraction Layer

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HAL and HEL

• HAL– Lowest level of software– Consists of manufacturer’s device drivers– DirectX figures out the COM interface needed

• HEL– Built on top of HAL– Allows emulation of missing hardware (e.g.

program still runs whether 3D graphics accelerator card is present or not)

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COM Interfaces

• The process of creating a COM interface is described in the text

• You do not need to create your own COM interfaces if you use DirectX

• DirectX provides wrappers round the COM stuff

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Creating COM Interfaces

• You begin by deriving an interface class from IUnknown (COM base class)

• Every derived class inherits 3 methods– QueryInterface( ) – used to request pointer

to interface– AddRef( ) – used to increase reference

count for COM object– Release( ) – decrements COM object

reference counter

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Creating COM Interfaces

• Basic technique is to create pointers to each device specific function and equate them to a generic function pointer

• DirectX will then be able to use the correct COM object when its function is referenced