Swing/BlurButton のバックアップ(No.8)

class BlurButton extends JButton {
  private final ConvolveOp op = new ConvolveOp(
      new Kernel(3, 3, new float[] {
    .05f, .05f, .05f,
    .05f, .60f, .05f,
    .05f, .05f, .05f
  }), ConvolveOp.EDGE_NO_OP, null);
  private BufferedImage buf;
  public BlurButton(String label) {
    super(label);
    //System.out.println(op.getEdgeCondition());
  }
  @Override protected void paintComponent(Graphics g) {
    if (isEnabled()) {
      super.paintComponent(g);
    } else {
      buf = Optional.ofNullable(buf).filter(bi -> bi.getWidth() == getWidth() && bi.getHeight() == getHeight())
                    .orElseGet(() -> new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB));
      Graphics2D g2 = buf.createGraphics();
      super.paintComponent(g2);
      g2.dispose();
      g.drawImage(op.filter(buf, null), 0, 0, null);
    }
  }
  @Override public Dimension getPreferredSize() {
    Dimension d = super.getPreferredSize();
    d.width += 3 * 3;
    return d;
  }
}