[Lazarus] Screenshot without the gnome applications menu

[Dave Coventry]

I am using


  ScreenDC := GetDC(0);
  MyBitmap.LoadFromDevice(ScreenDC);
  ReleaseDC(0,ScreenDC);

To grab a screenshot of my desktop. Is there any way of working out
the size of the gmone application menu so that I can exclude it from
my screen grab?