JPopupMenuに半透明の影を付ける

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Summary

Robotで画面をキャプチャーするなどして、半透明の影をJPopupMenuに付けます。

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Source Code Examples

class ShadowBorder extends AbstractBorder {
  private final int xoff, yoff;
  private final transient BufferedImage screen;
  private transient BufferedImage shadow;

  public ShadowBorder(int x, int y, JComponent c, Point p) {
    super();
    this.xoff = x;
    this.yoff = y;
    BufferedImage bi = null;
    try {
      Robot robot = new Robot();
      Dimension d = c.getPreferredSize();
      bi = robot.createScreenCapture(
          new Rectangle(p.x, p.y, d.width + xoff, d.height + yoff));
    } catch (AWTException ex) {
      ex.printStackTrace();
    }
    screen = bi;
  }

  @Override public Insets getBorderInsets(Component c) {
    return new Insets(0, 0, xoff, yoff);
  }

  @Override public void paintBorder(
        Component c, Graphics g, int x, int y, int w, int h) {
    if (screen == null) {
      return;
    }
    if (shadow == null || shadow.getWidth() != w || shadow.getHeight() != h) {
      shadow = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
      Graphics2D g2 = shadow.createGraphics();
      g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                          RenderingHints.VALUE_ANTIALIAS_ON);
      g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, .2f));
      g2.setPaint(Color.BLACK);
      for (int i = 0; i < xoff; i++) {
        g2.fillRoundRect(xoff, xoff, w - xoff - xoff + i, h - xoff - xoff + i, 4, 4);
      }
      g2.dispose();
    }
    Graphics2D g2d = (Graphics2D) g.create();
    g2d.drawImage(screen, 0, 0, c);
    g2d.drawImage(shadow, 0, 0, c);
    g2d.setPaint(c.getBackground()); //??? 1.7.0_03
    g2d.fillRect(x, y, w - xoff, h - yoff);
    g2d.dispose();
  }
}
View in GitHub: Java, Kotlin

Description

ポップアップメニューに半透明の影をつける際、フレームからはみ出すかどうかで異なる処理を行っています。

上記のサンプルコードは、フレームからはみ出す場合に使用するBorderクラスです。

  • フレーム内
    • JPopupMenu#paintComponentメソッドで半透明の影を描画
  • フレーム外
    • Robotを使って画面全体をキャプチャーしこれを利用して半透明の影をBorderとして作成
    • このためポップアップメニューがはみ出しても影を付けることが可能
  • 1.6.0_10以上の場合フレーム外でもRobotを使用せず以下のようにJPopupMenuの上位Windowの背景色を透明にすれば影の描画が可能 
    class DropShadowPopupMenu extends JPopupMenu {
  private static final int OFFSET = 4;
  private final Dimension dim = new Dimension();
  private transient BufferedImage shadow;

  @Override public void updateUI() {
    setBorder(null);
    super.updateUI();
    Border inner = getBorder();
    Border outer = BorderFactory.createEmptyBorder(0, 0, OFFSET, OFFSET);
    setBorder(BorderFactory.createCompoundBorder(outer, inner));
  }

  @Override public boolean isOpaque() {
    return false;
  }

  @Override protected void paintComponent(Graphics g) {
    // super.paintComponent(g);
    Graphics2D g2 = (Graphics2D) g.create();
    g2.drawImage(shadow, 0, 0, this);
    g2.setPaint(getBackground()); // ??? 1.7.0_03
    g2.fillRect(0, 0, getWidth() - OFFSET, getHeight() - OFFSET);
    g2.dispose();
  }

  @Override public void show(Component c, int x, int y) {
    Dimension d = getPreferredSize();
    int w = d.width;
    int h = d.height;
    if (dim.width != w || dim.height != h) {
      dim.setSize(w, h);
      shadow = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
      Graphics2D g2 = shadow.createGraphics();
      g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                          RenderingHints.VALUE_ANTIALIAS_ON);
      g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, .2f));
      g2.setPaint(Color.BLACK);
      for (int i = 0; i < OFFSET; i++) {
        g2.fillRoundRect(
            OFFSET, OFFSET, w - OFFSET - OFFSET + i,
            h - OFFSET - OFFSET + i, 4, 4);
      }
      g2.dispose();
    }
    EventQueue.invokeLater(() -> {
      Window top = SwingUtilities.getWindowAncestor(this);
      if (top != null && top.getType() == Window.Type.POPUP) {
        // Popup$HeavyWeightWindow
        top.setBackground(new Color(0x0, true)); // JDK 1.7.0
      }
    });
    super.show(c, x, y);
  }
}

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