static L<Component> stackElementsShowing(final DynamicStack stack) {
  ret swing(func -> L<Component> {
    new L<Component> l;
    if (!stack.isShowing()) ret l;
    JScrollPane sp = enclosingScrollPane(stack);
    if (sp == null) ret l;
    JViewport vp = sp.getViewport();
    Rect vpRect = toRect(vp.getBounds());
    for (Component c : stack.components())
      if (rectsIntersect(vpRect, boundsInParent(c, vp)))
        l.add(c);
    ret l;
  });
}