Swing/Gradient のバックアップ(No.20)

class GradientSeparatorUI extends BasicSeparatorUI {
  private Color bgc, ssc, shc;

  public static ComponentUI createUI(JComponent c) {
    return new GradientSeparatorUI();
  }
  private void updateColors(JComponent j) {
    Color c = UIManager.getColor("Panel.background");
    bgc = c instanceof ColorUIResource ? c : j.getBackground();
    c = UIManager.getColor("Separator.shadow");
    ssc = c instanceof ColorUIResource ? c : j.getBackground().brighter();
    c = UIManager.getColor("Separator.highlight");
    shc = c instanceof ColorUIResource ? c : j.getBackground().darker();
  }
  @Override public void installUI(JComponent c) {
    super.installUI(c);
    updateColors(c);
  }
  @Override public void paint(Graphics g, JComponent c) {
    if (c instanceof JSeparator) {
      Graphics2D g2 = (Graphics2D) g.create();
      Dimension s = c.getSize();
      JSeparator js = (JSeparator) c;
      if (js.getOrientation() == JSeparator.VERTICAL) {
        g2.setPaint(new GradientPaint(0, 0, ssc, 0, s.height, bgc, true));
        g2.fillRect(0, 0, 1, s.height);
        g2.setPaint(new GradientPaint(0, 0, shc, 0, s.height, bgc, true));
        g2.fillRect(1, 0, 1, s.height);
      } else {
        g2.setPaint(new GradientPaint(0, 0, ssc, s.width, 0, bgc, true));
        g2.fillRect(0, 0, s.width, 1);
        g2.setPaint(new GradientPaint(0, 0, shc, s.width, 0, bgc, true));
        g2.fillRect(0, 1, s.width, 1);
      }
      g2.dispose();
    }
  }
}