Swing/RippleBorder のバックアップ(No.14)

class RippleBorder extends EmptyBorder {
  private final Timer animator;
  private final JComponent comp;
  private float count = 1f;

  public RippleBorder(JComponent c, int width) {
    super(width, width, width, width);
    this.comp = c;
    animator = new Timer(80, new ActionListener() {
      @Override public void actionPerformed(ActionEvent e) {
        comp.repaint();
        count += .9f;
      }
    });
    comp.addMouseListener(new MouseAdapter() {
      @Override public void mouseEntered(MouseEvent e) {
        comp.setForeground(Color.RED);
        animator.start();
      }

      @Override public void mouseExited(MouseEvent e) {
        comp.setForeground(Color.BLACK);
      }
    });
  }

  @Override public void paintBorder(Component c, Graphics g, int x, int y, int w, int h) {
    if (!animator.isRunning()) {
      super.paintBorder(c, g, x, y, w, h);
      return;
    }
    Graphics2D g2 = (Graphics2D) g;
    g2.setPaint(Color.WHITE);
    float a = 1f / count;
    if (.12f - a > 1.0e-2) {
      a = 0f;
    }
    g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, a));
    Insets i = getBorderInsets();
    int xx = i.left - (int) count;
    int yy = i.top - (int) count;
    int ww = i.left + i.right - (int) (count * 2f);
    int hh = i.top + i.bottom - (int) (count * 2f);
    g2.setStroke(new BasicStroke(count * 1.2f));
    g2.drawRoundRect(xx, yy, w - ww, h - hh, 10, 10);
    if (xx < 0 && animator.isRunning()) {
      count = 1f;
      animator.stop();
    }
  }
}