private void InitDevice()
{
Debug.Assert( _device != null );
// get device caps
_devCaps = _device.Capabilities;
// get our device creation parameters
_devParms = _device.CreationParameters;
// get our back buffer pixel format
D3D.Surface back = _device.GetBackBuffer( 0, 0 );
_bbPixelFormat = back.Description.Format;
}