sclass DesktopPaneWithSkyPicture_autoUnload extends JDesktopPane {
  S imageID;
  BufferedImage image;
  new RestartableCountdown countdown;
  double autoUnloadAfter = 60.0;
  bool verbose = true;
  
  *(S *imageID, BufferedImage *image) {}
  
  protected void paintComponent(Graphics g) {  
    paintSkyBackground(this, g, _getImage());
  }
  
  BufferedImage _getImage() {
    ret swing(func -> BufferedImage {
      if (image == null) {
        long time = sysNow();
        image = loadImage2(imageID);
        if (verbose) _print("Background image loaded in " + elapsedMS(time) + " ms");
      }
      countdown.start(autoUnloadAfter, r-awt {
        if (image != null) {
          image = null;
          if (verbose) _print("Background image released");
        }
      });
      ret image;
    });
  }
}

static JDesktopPane jDesktopPaneWithSkyPicture_autoUnload(fS imageID, Color background) {
  ret setBackground(background, swingNu(DesktopPaneWithSkyPicture_autoUnload, imageID, loadImage2(imageID)));
}