The IDirectDrawVideoPort::GetVideoLine method retrieves the current line of video being written to the frame buffer.
HRESULT GetVideoLine(
LPDWORD lpdwLine
);
If the method succeeds, the return value is DD_OK.
If the method fails, the return value may be one of the following error values:
| DDERR_INVALIDOBJECT |
| DDERR_INVALIDPARAMS |
| DDERR_UNSUPPORTED |
| DDERR_VERTICALBLANKINPROGRESS |
| DDERR_VIDEONOTACTIVE |
The value this method retrieves reflects the true video line being written, relative to the field height, before any prescaling occurs.