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IDirectDraw7::GetAvailableVidMem method (ddraw.h)

  • Article

Retrieves the total amount of display memory available and the amount of display memory currently free for a given type of surface.

Syntax

HRESULT GetAvailableVidMem(
  [in]  LPDDSCAPS2 unnamedParam1,
  [out] LPDWORD    unnamedParam2,
  [out] LPDWORD    unnamedParam3
);

Parameters

[in] unnamedParam1

A pointer to a DDSCAPS2 structure that indicates the hardware capabilities of the proposed surface.

[out] unnamedParam2

A pointer to a variable that receives the total amount of display memory available, in bytes. The value received reflects the total video memory, minus the video memory required for the primary surface and any private caches that the display driver reserves.

[out] unnamedParam3

A pointer to a variable that receives 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 value

If the method succeeds, the return value is DD_OK.

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

  • DDERR_INVALIDCAPS
  • DDERR_INVALIDOBJECT
  • DDERR_INVALIDPARAMS
  • DDERR_NODIRECTDRAWHW

Remarks

The following C++ example demonstrates how to use 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 IDirectDraw7 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, GetAvailableVidMem returns different amounts of video memory depending on whether the surface can be used as a 3-D texture. If the surface can be used for 3-D textures, GetAvailableVidMem returns the sum of the local video memory and the non-local video memory on AGP systems.

GetAvailableVidMem 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).

GetAvailableVidMem was not implemented in the previous DirectX IDirectDraw interface version.

Requirements

Requirement Value
Target Platform Windows
Header ddraw.h
Library Ddraw.lib
DLL Ddraw.dll

See also

IDirectDraw7