IDirect3DViewport::SetBackgroundDepth
HRESULT SetBackgroundDepth(LPDIRECTDRAWSURFACE lpDDSurface);
Sets the background-depth field for the viewport.
·Returns D3D_OK if successful, or an error otherwise, which may be one of the following values:
lpDDSurface
Address of the DirectDrawSurface object representing the background depth.
The z-buffer is filled with the specified depth field when the IDirect3DViewport::Clear method is called and the D3DCLEAR_ZBUFFER flag is specified. The bit depth must be 16 bits.