HRESULT Update();
Copies the image that has been rendered to the display. It also provides a heartbeat function to the device driver.
·Returns D3DRM_OK if successful, or an error otherwise. For a list of possible return codes, see Direct3D Retained-Mode Return Values.
Each call to this method causes the system to call an application-defined callback function, D3DRMUPDATECALLBACK. To add a callback function, use the IDirect3DRMDevice::AddUpdateCallback method.