Selects the method used for image compositing.
HRESULT retVal = object.SetCompositeOperation(CompOp);
DXSURFMODCOMPOP value that determines the method used for compositing.
By default, the compositing operation is DXSURFMOD_COMP_OVER.
When the compositing operation is DXSURFMOD_COMP_OVER, the foreground surface is composited over the background surface. If there is no background surface, the foreground surface is composited over the fill color.
When the compositing operation is DXSURFMOD_COMP_ALPHA_MASK, the foreground surface uses the alpha values of the background surface to weight the foreground surface pixel values; the colors of the background surface are ignored. If there is no background surface, the alpha value of the fill color is used to weight the foreground surface pixel values. However, this is less efficient than using the IDXSurfaceModifier::SetOpacity method.