JLayeredPane和绘画

Question

我正在编写一个具有JLayeredPane（称为图层）的应用程序，其中包含两个不同图层的JPanel。我覆盖了底部JPanel的paintComponent方法（称之为grid_panel），因此它绘制了一个网格，并在顶部绘制了一个paintComponent方法（称之为circuit_panel），因此它绘制了一个电路。

以下是结构摘要：

layers -
       |-circuit_panel (on top)
       |-grid_panel (at bottom)

我希望grid_panel保持静态，即不进行任何重绘（初始的除外），因为它不会改变。

麻烦的是，每当我调用circuit_panel.repaint（）时，grid_panel也会被重新绘制！这绝对没有效率。

我认为这是由于JLayeredPane的热切绘画行为。有没有办法在JLayeredPane中禁用此功能？

如果你有兴趣看到上述效果，我写了一个小的演示程序：

public class Test2 extends JFrame {

    public Test2() {
        JLayeredPane layers = new JLayeredPane();
        layers.setPreferredSize(new Dimension(600, 400));

        MyPanel1 myPanel1 = new MyPanel1();
        MyPanel2 myPanel2 = new MyPanel2();
        myPanel1.setSize(600, 400);
        myPanel2.setSize(600, 400);
        myPanel1.setOpaque(false);
        myPanel2.setOpaque(false);
        myPanel2.addMouseListener(new MyMouseListener(myPanel2));

        layers.add(myPanel1, new Integer(100)); // At bottom
        layers.add(myPanel2, new Integer(101)); // On top

        this.getContentPane().add(layers, BorderLayout.CENTER);
        this.setSize(600, 400);
    }

    class MyPanel1 extends JPanel {

        Color getRandomColor() {
            int r = (int) (256 * Math.random());
            int g = (int) (256 * Math.random());
            int b = (int) (256 * Math.random());
            return new Color(r, g, b);
        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g;
            g2d.setColor(getRandomColor());
            g2d.fillRoundRect(30, 30, 60, 60, 5, 5);
        }
    }

    class MyPanel2 extends JPanel {

        Color getRandomColor() {
            int r = (int) (256 * Math.random());
            int g = (int) (256 * Math.random());
            int b = (int) (256 * Math.random());
            return new Color(r, g, b);
        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g;
            g2d.setColor(getRandomColor());
            g2d.fillRoundRect(45, 45, 75, 75, 5, 5);
        }
    }

    class MyMouseListener extends MouseAdapter {

        JPanel panel;

        MyMouseListener(JPanel panel) {
            this.panel = panel;
        }

        @Override
        public void mouseClicked(MouseEvent e) {
            panel.repaint();
        }
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                (new Test2()).setVisible(true);
            }
        });
    }
}

Answer 1

正如您所发现的，BufferedImage是缓存复杂内容以实现高效渲染的有效方法; CellTest就是一个例子。显示here的flyweight渲染器是另一种方法。最后，我以一种可以使实验更容易的方式重新考虑了你的指导性示例。

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JLayeredPane;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

/** @see https://stackoverflow.com/q/9625495/230513 */
public class LayerDemo extends JFrame {

    private static final Dimension d = new Dimension(320, 240);

    public LayerDemo() {
        JLayeredPane layers = new JLayeredPane();
        layers.setPreferredSize(d);

        layers.add(new LayerPanel(1 * d.height / 8), 100);
        layers.add(new LayerPanel(2 * d.height / 8), 101);
        layers.add(new LayerPanel(3 * d.height / 8), 102);

        this.add(layers, BorderLayout.CENTER);
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.pack();
        this.setLocationByPlatform(true);
    }

    private static class LayerPanel extends JPanel {

        private static final Random r = new Random();
        private int n;
        private Color color = new Color(r.nextInt());

        public LayerPanel(int n) {
            this.n = n;
            this.setOpaque(false);
            this.setBounds(n, n, d.width / 2, d.height / 2);
            this.addMouseListener(new MouseHandler(this));
        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g;
            g2d.setRenderingHint(
                RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);
            g2d.setColor(color);
            g2d.fillRoundRect(0, 0, getWidth(), getHeight(), 16, 16);
            g2d.setColor(Color.black);
            g2d.drawString(String.valueOf(n), 5, getHeight() - 5);
        }

        private void update() {
            color = new Color(r.nextInt());
            repaint();
        }
    }

    private static class MouseHandler extends MouseAdapter {

        LayerPanel panel;

        MouseHandler(LayerPanel panel) {
            this.panel = panel;
        }

        @Override
        public void mouseClicked(MouseEvent e) {
            panel.update();
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                (new LayerDemo()).setVisible(true);
            }
        });
    }
}