The IDirect3DViewport3::GetBackgroundDepth2 method retrieves a DirectDraw surface that represents the current background-depth field associated with the viewport.
HRESULT GetBackgroundDepth2(
  LPDIRECTDRAWSURFACE4* lplpDDS,
  LPBOOL lpValid
); 
 If the method succeeds, the return value is D3D_OK.
If the method fails, the return value may be one of the following values:
| DDERR_INVALIDOBJECT | 
| DDERR_INVALIDPARAMS | 
  Windows NT/2000: Requires Windows 2000.
  Windows 95/98: Requires Windows 95 or later. Available as a redistributable for Windows 95.
  Header: Declared in d3d.h.
  Import Library: Use ddraw.lib.