Nevermind, I've figured it out:
Global mouse_down Global mouse_X Global mouse_Y Global mouse_dX Global mouse_dY FlushMouse While 1 WaitEvent() Select EventID() Case EVENT_MOUSEDOWN mouse_down=EventData() Case EVENT_MOUSEUP mouse_down=0 Case EVENT_MOUSEMOVE mouse_dX=EventX()-mouse_X mouse_dY=EventY()-mouse_Y mouse_X=EventX() mouse_Y=EventY()