DirectDraw (DirectX 7)

This article introduces the concepts behind DirectDraw with DirectX v8 interfaces.

DirectDraw interfaces

There are four DirectDraw interfaces, all derived from IUnknown. The following interface identifiers omits any specific version number.

  • IDirectDraw - the main interface which effectively represents the GPU
  • IDirectDrawSurface - represents the display surface that can reside in VRAM or system memory. Two types of surface:
    • Primary surface - represents the video buffer being rasterised and displayed on screen
    • Seconday surface - represents the back buffer (off-screen) scene
  • IDirectDrawPalette - handles the 256-colour mode colour palette
  • IDirectDrawClipper - assists with clipping bitmap and raster operations, typically for windowed applications

Creating the DirectDraw object

There are principally three ways to create DirectDraw objects (based on IDirectDraw7):

  • Use DirectDrawCreate() to get an IDirectDraw 1.0 interface IDirectDraw, and then via QueryInterface() get the latest IDirectDraw7 interface
  • Use a low-level COM approach to get IDirectDraw7
  • Use DirectDrawCreateEx() to get hold of IDirectDraw7

Using DirectDrawCreate() to get IDirectDraw7

DirectDrawCreate() has three parameters:

  1. lpGUID - GUID of the display driver to use; set to NULL to use the system default
  2. lplpDD - a pointer to a pointer that receives IDirectDraw
  3. pUnkOuter - advanced feature, leave as NULL
// standard DirectDraw 1.0
LPDIRECTDRAW lpdd = NULL;

// FAILED is a DirectX macro (contrast to SUCCEEDED)
if (FAILED(DirectDrawCreate(NULL, &lpdd, NULL))){
    // problem starting up 1.0, return
}

// got DirectDraw 1.0, let's update to 7.0
LPDIRECTDRAW lpdd7 = NULL;

if (FAILED(lpdd->QueryInterface(IID_DirectDraw7, (LPVOID *)&lpdd7))){
    // problem starting up 7.0; clean up then return
}

// release 1.0, don't need it anymore
lpdd->Release();
lpdd = NULL;

The IID_DirectDraw7 naming convention refers to the interface ID (IID) and also applies to other DirectX components e.g.

  • IID_DirectSoundX
  • IID_DirectInputX

where X is the version number.

The COM approach to get IDirectDraw7

This approach requires knowledge of the interface ID (IID).

// try to load COM libraries
if (FAILED(CoInitialize(NULL))){
    // failed to load COM libraries, return
}

LPDIRECTDRAW lpdd7 = NULL;

if (FAILED(CoCreateInstance(&CLSID_DirectDraw, NULL, CLSCTX_ALL, &IID_IDirectDraw7, &lpdd7))){
    // failed to create DirectDraw 7 object, return
}

if (FAILED(IDirectDraw7_Initialize(lpdd7, NULL))){
    // failed to initialise DirectDraw 7.0 object, clean up and return
}

// could also use this instead to initialise
if (FAILED(lpdd7->Initialize(NULL))){
    // failed to initialise DirectDraw 7.0 object again, clean up and return
}

// finished with COM
CoUninitialize();

Using DirectDrawCreateEx() to get IDirectDraw7

This is a bit quicker to invoke.

LPDIRECTDRAW lpdd7 = NULL;

DirectDrawEx(NULL, (void **)&lpdd7, IID_DirectDraw7, NULL);

The function DirectDrawEx() has four parameters:

  • lpGUID - the GUID of the driver, NULL for active display
  • lplpDD - receiver of the interface
  • iid - interface ID of the interface requested
  • pUnkOther - advanced COM, leave as NULL