gdkScreenGetMonitorGeometry.gtkMenuSetMonitor(object, monitor.num)objectGtkMenumonitor.numGtkMenuPositionFunc if the
menu should not appear on the same monitor as the pointer. This
information can't be reliably inferred from the coordinates returned
by a GtkMenuPositionFunc, since, for very long menus, these coordinates
may extend beyond the monitor boundaries or even the screen boundaries.
Since 2.4