virtual Image MouseEvent(int event, Point p, int zdelta, dword keyflags)

Image MyCtrl::MouseEvent(int event, Point p, int zdelta, dword keyflags) {
   if(event == MOUSELEAVE) {
      //do something here
      return NULL;
   }
   else {
       return Ctrl::MouseEvent(event, p, zdelta, keyflags);
   }
};