// f : voidfunc(Pt) - point can be null, then mouse has exited
static <A extends JComponent> A callFunctionOnMouseMove(final A c, final O f) {
  if (c != null && f != null) 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); }
    };
    c.addMouseMotionListener(ma);
    c.addMouseListener(ma);
  }
  ret c;
}