JScrollPane内のコンテンツがJViewportの幅より大きい場合その右端に影を描画する

class ScrollPaneLayerUI extends LayerUI<JScrollPane> {
  @Override public void paint(Graphics g, JComponent c) {
    super.paint(g, c);
    if (c instanceof JLayer) {
      JScrollPane scroll = (JScrollPane) ((JLayer<?>) c).getView();
      Rectangle rect = scroll.getViewportBorderBounds();
      BoundedRangeModel m = scroll.getHorizontalScrollBar().getModel();
      int extent = m.getExtent();
      int maximum = m.getMaximum();
      int value = m.getValue();
      if (value + extent < maximum) {
        int w = rect.width;
        int h = rect.height;
        int shd = 6;
        Graphics2D g2 = (Graphics2D) g.create();
        g2.translate(rect.x + w - shd, rect.y);
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setPaint(new Color(0x08_00_00_00, true));
        for (int i = 0; i < shd; i++) {
          g2.fillRect(i, 0, shd - i, h);
        }
        g2.fillRect(shd - 2, 0, 2, h); // Make the edge a bit darker
        g2.dispose();
      }
    }
  }
}