// f : voidfunc(Pt) - point can be null, then mouse has exited
static void imageSurfaceOnMouseMove(final ImageSurface is, final O f) {
  swing {
    MouseAdapter ma = new MouseAdapter {
      public void mouseMoved(MouseEvent e) {
        pcallF(f, is.pointFromEvent(e));
      }
      
      public void mouseEntered(MouseEvent e) {
        pcallF(f, is.pointFromEvent(e));
      }
  
      public void mouseExited(MouseEvent e) {
        pcallF(f, (Pt) null);
      }
    };
    is.addMouseMotionListener(ma);
    is.addMouseListener(ma);
  }
}