sclass ButtonImageLoader {
  DynamicStack stack;
  Set<JButton> loadedButtons = weakIdentityHashSet();
  DeQ loadQ;
  JScrollPane scrollPane;
  ChangeListener changeListener;

  *(final DynamicStack *stack) {
    bindToComponent(stack, r {
      scrollPane = enclosingScrollPane(stack);
      changeListener = scrollPaneOnScroll(scrollPane, r { update() });
      update();
    }, r {
      if (scrollPane != null) {
        scrollPane.getViewport().removeChangeListener(changeListener);
        scrollPane = null;
        changeListener = null;
      }
    });
  }
  
  void update() {
    for (final JButton b : reversed((L<JButton>) (L) stackElementsShowing(buttons))) {
      //if (add(loadedButtons, b)) pcall { // will strangely not work
      if (add_byContains(loadedButtons, b)) pcall {
        TextImageAction tia = makeNiceButtons_map.get(b);
        if (tia == null) continue with print("no tia");
        final File f = filesForNiceButtons_map.get(tia);
        if (f == null) continue with print("no file");
        if (loadQ == null) loadQ = startDeQ();
        loadQ.addFirst(r {
          setButtonImage(b, loadPreviewImageWithExactHeight(128, f));
          print("Loaded: " + f);
          print("Size: " + l(loadedButtons));
        });
      }
    }
  }
}