static JPanel scrollable_trackHeight(final Component component) {
  class P extends SingleComponentPanel implements Scrollable {
    *() { super(component); }
    
    public Dimension getPreferredScrollableViewportSize() { ret getPreferredSize(); }
    
    public int getScrollableUnitIncrement(Rectangle visibleRect, int orientation, int direction) { return 20; }

    public int getScrollableBlockIncrement(Rectangle visibleRect, int orientation, int direction) {
      ret (direction == SwingConstants.HORIZONTAL ? visibleRect.width : visibleRect.height)*5/6;
    }

    public bool getScrollableTracksViewportWidth() { false; }
    public boolean getScrollableTracksViewportHeight() { true; }
  }
  ret swing(func -> P { new P });
}

Began life as a copy of #1014106