IDirectDraw7::GetAvailableVidMem

The IDirectDraw7::GetAvailableVidMem method retrieves the total amount of display memory available and the amount of display memory currently free for a given type of surface.

HRESULT GetAvailableVidMem(
  LPDDSCAPS2 lpDDSCaps2,  
  LPDWORD    lpdwTotal,   
  LPDWORD    lpdwFree     
);

Parameters

lpDDSCaps2

Address of a DDSCAPS2 structure that indicates the hardware capabilities of the proposed surface.

lpdwTotal

Address of a variable to be filled with the total amount of display memory available, in bytes. The value retrieved reflects the total video memory, minus the video memory required for the primary surface and any private caches that the display driver reserves.

lpdwFree

Address of a variable to be filled with the amount of display memory currently free that can be allocated for a surface that matches the capabilities specified by the structure at lpDDSCaps2.

Return Values

If the method succeeds, the return value is DD_OK.

If it fails, the method can return one of the following error values:

If NULL is passed to either lpdwTotal or lpdwFree, the value for that parameter is not returned.

Remarks

The following C++ example demonstrates how to use IDirectDraw7::GetAvailableVidMem to determine both the total and free display memory available for texture-map surfaces:

// For this example, the lpDD variable is a valid 
// pointer to an IDirectDraw interface.
LPDIRECTDRAW7 lpDD;
DDSCAPS2      ddsCaps2; 
DWORD         dwTotal; 
DWORD         dwFree;
HRESULT       hr; 
 
hr = lpDD->QueryInterface(IID_IDirectDraw7, &lpDD); 
if (FAILED(hr))
    return hr; 
 
// Initialize the structure.
ZeroMemory(&ddsCaps2, sizeof(ddsCaps2));
 
ddsCaps2.dwCaps = DDSCAPS_TEXTURE; 
hr = lpDD->GetAvailableVidMem(&ddsCaps2, &dwTotal, &dwFree); 
if (FAILED(hr))
    return hr;

If the surface has the DDSCAPS_VIDEOMEMORY flag set, this method will return different amounts of video memory depending on whether or not the surface can be used as a 3-D texture. If the surface can be used for 3-D textures, the GetAvailableVidMem method will return the sum of the local video memory and the non-local video memory on AGP systems.

This method provides only a snapshot of the current display-memory state. The amount of free display memory is subject to change as surfaces are created and released. Therefore, you should use the free memory value only as an approximation. In addition, a particular display adapter card might make no distinction between two different memory types. For example, the adapter might use the same portion of display memory to store z-buffers and textures. So, allocating one type of surface (for example, a z-buffer) can affect the amount of display memory available for another type of surface (textures). Therefore, it is best to first allocate an application's fixed resources (such as front and back buffers and z-buffers) before determining how much memory is available for dynamic use (such as texture mapping).

This method was not implemented in the IDirectDraw interface.

Requirements

  Windows NT/2000: Requires Windows 2000.
  Windows 95/98: Requires Windows 98.
  Header: Declared in ddraw.h.