HRESULT GetScanLine(LPDWORD lpdwScanLine);
Returns the scan line that is currently being drawn on the monitor.
·Returns DD_OK if successful, or one of the following error values otherwise:
DDERR_INVALIDOBJECT DDERR_INVALIDPARAMS
DDERR_UNSUPPORTED DDERR_VERTICALBLANKINPROGRESS
lpdwScanLine
Address of the doubleword to contain the scan line the display is currently on.