// component can be a custom-painted JComponent
static JWindow showAlwaysOnTopTranslucentWindow(Rect bounds, Color backgroundWithAlpha, JComponent component default null) {
  ret swing(() -> {
    new JWindow f;
    f.setAlwaysOnTop(true);
    f.setBackground(backgroundWithAlpha);
    f.setBounds(toRectangle(bounds));
    JComponent c = component;
    if (c == null)
      c = onClickDisposeWindow(jpanel());
    add(f, c);
    f.setLocationRelativeTo(null);
    f.setVisible(true);
    vmBus_send newAlwaysOnTopWindow(f);
    ret f;
  });
}