static float darkenScreenArea_factor = 0.5f;

static JWindow darkenScreenArea(Rectangle r, double seconds) {

  ret disposeWindowAfter(iround(seconds*1000),

    darkenScreenArea(r));

}

static JWindow darkenScreenArea(final Rectangle r) {

  ret (JWindow) swingAndWait(func {

    Rectangle r2 = maxWindowBounds().intersection(r);

    if (neq(r, r2)) warn("darkenScreenArea: Rectangle cropped");

    if (r2.isEmpty()) null;

    BufferedImage img = shootScreen2(r2);

    RescaleOp op = new RescaleOp(darkenScreenArea_factor, 0, null);

    img = op.filter(img, null);

    JLabel label = new JLabel(imageIcon(img));

    new JWindow w;

    w.setBounds(r2);

    w.add(label);

    w.setAlwaysOnTop(true);

    w.setVisible(true);

    ret w;

  });

}