JPanel 上活动绘图之上的 JTextFields、线程问题

Question

有没有人尝试过使用 Swing 构建适当的多缓冲渲染环境在其上可以添加 Swing 用户界面元素？

在本例中，我在背景上绘制了一个动画红色矩形。背景不需要每帧都更新，因此我将其渲染到 BufferedImage 上，并仅重绘清除矩形先前位置所需的部分。请参阅下面的完整代码，这扩展了 @trashgod 在上一个线程中给出的示例， 这里。

到目前为止，一切都很好;动画流畅，CPU占用率低，无闪烁。

然后，我将 JTextField 添加到 Jpanel（通过单击屏幕上的任意位置），并通过单击文本框内部来聚焦于它。现在，每次光标闪烁时，清除矩形以前的位置都会失败，请参见下图。

我很好奇是否有人知道为什么会发生这种情况（Swing 不是线程安全的？图像是异步绘制的？）以及在什么方向寻找可能的解决方案。

这是在 Mac OS 10.5、Java 1.6 上

_{（来源：arttech.nl）}

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.GraphicsConfiguration;
import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.Insets;
import java.awt.Rectangle;
import java.awt.Transparency;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.Timer;

public class NewTest extends JPanel implements 
    MouseListener, 
    ActionListener, 
    ComponentListener, 
    Runnable 
{

JFrame f;
Insets insets;
private Timer t = new Timer(20, this);
BufferedImage buffer1;
boolean repaintBuffer1 = true;
int initWidth = 640;
int initHeight = 480;
Rectangle rect;

public static void main(String[] args) {
    EventQueue.invokeLater(new NewTest());
}

@Override
public void run() {
    f = new JFrame("NewTest");
    f.addComponentListener(this);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.add(this);
    f.pack();
    f.setLocationRelativeTo(null);
    f.setVisible(true);
    createBuffers();
    insets = f.getInsets();
    t.start();
}

public NewTest() {
    super(true);
    this.setPreferredSize(new Dimension(initWidth, initHeight));
    this.setLayout(null);
    this.addMouseListener(this);
}

void createBuffers() {
    int width = this.getWidth();
    int height = this.getHeight();

    GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
    GraphicsDevice gs = ge.getDefaultScreenDevice();
    GraphicsConfiguration gc = gs.getDefaultConfiguration();

    buffer1 = gc.createCompatibleImage(width, height, Transparency.OPAQUE);        

    repaintBuffer1 = true;
}

@Override
protected void paintComponent(Graphics g) {
    int width = this.getWidth();
    int height = this.getHeight();

    if (repaintBuffer1) {
        Graphics g1 = buffer1.getGraphics();
        g1.clearRect(0, 0, width, height);
        g1.setColor(Color.green);
        g1.drawRect(0, 0, width - 1, height - 1);
        g.drawImage(buffer1, 0, 0, null);
        repaintBuffer1 = false;
    }

    double time = 2* Math.PI * (System.currentTimeMillis() % 5000) / 5000.;
    g.setColor(Color.RED);
    if (rect != null) {
        g.drawImage(buffer1, rect.x, rect.y, rect.x + rect.width, rect.y + rect.height, rect.x, rect.y, rect.x + rect.width, rect.y + rect.height, this);
    }
    rect = new Rectangle((int)(Math.sin(time) * width/3 + width/2 - 20), (int)(Math.cos(time) * height/3 + height/2) - 20, 40, 40);
    g.fillRect(rect.x, rect.y, rect.width, rect.height);
}

@Override
public void actionPerformed(ActionEvent e) {
    this.repaint();
}

@Override
public void componentHidden(ComponentEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void componentMoved(ComponentEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void componentResized(ComponentEvent e) {
    int width = e.getComponent().getWidth() - (insets.left + insets.right);
    int height = e.getComponent().getHeight() - (insets.top + insets.bottom);
    this.setSize(width, height);
    createBuffers();
}

@Override
public void componentShown(ComponentEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mouseClicked(MouseEvent e) {
    JTextField field = new JTextField("test");
    field.setBounds(new Rectangle(e.getX(), e.getY(), 100, 20));
    this.add(field);
    repaintBuffer1 = true;
}

@Override
public void mouseEntered(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mouseExited(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mousePressed(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mouseReleased(MouseEvent arg0) {
    // TODO Auto-generated method stub

}
}

Answer 1

NewTest 扩展 JPanel；但是因为您没有在每次调用 paintComponent() 时绘制每个像素，所以您需要调用超类的方法并删除旧的绘图：

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    int width = this.getWidth();
    int height = this.getHeight();
    g.setColor(Color.black);
    g.fillRect(0, 0, width, height);
    ...
}

附录：正如您所注意到的，设置背景颜色构造函数不需要在 paintComponent() 中填充面板，而 super.paintComponent() 允许文本字段正确运行。正如您所观察到的，提议的解决方法很脆弱。相反，应简化代码并根据需要进行优化。例如，您可能不需要复杂的插入、额外缓冲区和组件侦听器。

附录 2：请注意，super.paintComponent() 调用 UI 委托的 update() 方法，"它用其背景颜色填充指定组件（如果其 opaque 属性为 true）。”您可以使用 setOpaque(false) 来阻止这种情况。

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GraphicsConfiguration;
import java.awt.GraphicsEnvironment;
import java.awt.Rectangle;
import java.awt.Transparency;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.Timer;

/** @see http://stackoverflow.com/questions/3256941 */
public class AnimationTest extends JPanel implements ActionListener {

    private static final int WIDE = 640;
    private static final int HIGH = 480;
    private static final int RADIUS = 25;
    private static final int FRAMES = 24;
    private final Timer timer = new Timer(20, this);
    private final Rectangle rect = new Rectangle();
    private BufferedImage background;
    private int index;
    private long totalTime;
    private long averageTime;
    private int frameCount;

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

            @Override
            public void run() {
                new AnimationTest().create();
            }
        });
    }

    private void create() {
        JFrame f = new JFrame("AnimationTest");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(this);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
        timer.start();
    }

    public AnimationTest() {
        super(true);
        this.setOpaque(false);
        this.setPreferredSize(new Dimension(WIDE, HIGH));
        this.addMouseListener(new MouseHandler());
        this.addComponentListener(new ComponentHandler());
    }

    @Override
    protected void paintComponent(Graphics g) {
        long start = System.nanoTime();
        super.paintComponent(g);
        int w = this.getWidth();
        int h = this.getHeight();
        g.drawImage(background, 0, 0, this);
        double theta = 2 * Math.PI * index++ / 64;
        g.setColor(Color.blue);
        rect.setRect(
            (int) (Math.sin(theta) * w / 3 + w / 2 - RADIUS),
            (int) (Math.cos(theta) * h / 3 + h / 2 - RADIUS),
            2 * RADIUS, 2 * RADIUS);
        g.fillOval(rect.x, rect.y, rect.width, rect.height);
        g.setColor(Color.white);
        if (frameCount == FRAMES) {
            averageTime = totalTime / FRAMES;
            totalTime = 0; frameCount = 0;
        } else {
            totalTime += System.nanoTime() - start;
            frameCount++;
        }
        String s = String.format("%1$5.3f", averageTime / 1000000d);
        g.drawString(s, 5, 16);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        this.repaint();
    }

    private class MouseHandler extends MouseAdapter {

        @Override
        public void mousePressed(MouseEvent e) {
            super.mousePressed(e);
            JTextField field = new JTextField("test");
            Dimension d = field.getPreferredSize();
            field.setBounds(e.getX(), e.getY(), d.width, d.height);
            add(field);
        }
    }

    private class ComponentHandler extends ComponentAdapter {

        private final GraphicsEnvironment ge =
            GraphicsEnvironment.getLocalGraphicsEnvironment();
        private final GraphicsConfiguration gc =
            ge.getDefaultScreenDevice().getDefaultConfiguration();
        private final Random r = new Random();

        @Override
        public void componentResized(ComponentEvent e) {
            super.componentResized(e);
            int w = getWidth();
            int h = getHeight();
            background = gc.createCompatibleImage(w, h, Transparency.OPAQUE);
            Graphics2D g = background.createGraphics();
            g.clearRect(0, 0, w, h);
            g.setColor(Color.green.darker());
            for (int i = 0; i < 128; i++) {
                g.drawLine(w / 2, h / 2, r.nextInt(w), r.nextInt(h));
            }
            g.dispose();
            System.out.println("Resized to " + w + " x " + h);
        }
    }
}

Answer 2

我找到了一个解决方法。

我认为发生了什么：每当需要更新 JTextfield 时（即每次光标闪烁时），都会调用 JPanel 的覆盖的 PaintComponent() ，但使用与 repaint() 调用时不同的 Graphics 参数。因此，每次光标闪烁时，我的矩形都会被清除并在错误的 Graphics 实例上重新绘制，从而使屏幕上看到的 Graphics 无效。

这有什么意义吗？如果确实如此，这对 Swing 来说不是一个奇怪的不便吗？

无论如何，通过保留调用来源的布尔值（activeRedraw），看起来我设法解决了这个问题。所以看来我终于找到了一种方法来进行主动绘图，而无需在每一帧上重新绘制整个屏幕区域，这意味着独立于窗口大小的低CPU使用率！

完整代码在这里：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.GraphicsConfiguration;
import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.Insets;
import java.awt.Rectangle;
import java.awt.Transparency;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.Timer;

public class NewTest extends JPanel implements 
    MouseListener, 
    ActionListener, 
    ComponentListener, 
    Runnable 
{

    JFrame f;
    Insets insets;
    private Timer t = new Timer(20, this);
    BufferedImage buffer1;
    boolean repaintBuffer1 = true;
    int initWidth = 640;
    int initHeight = 480;
    Rectangle rect;
    boolean activeRedraw = true;

    public static void main(String[] args) {
        EventQueue.invokeLater(new NewTest());
    }

    @Override
    public void run() {
        f = new JFrame("NewTest");
        f.addComponentListener(this);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(this);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
        createBuffers();
        insets = f.getInsets();
        t.start();
    }

    public NewTest() {
        super(true);
        this.setPreferredSize(new Dimension(initWidth, initHeight));
        this.setLayout(null);
        this.addMouseListener(this);
    }

    void createBuffers() {
        int width = this.getWidth();
        int height = this.getHeight();

        GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
        GraphicsDevice gs = ge.getDefaultScreenDevice();
        GraphicsConfiguration gc = gs.getDefaultConfiguration();

        buffer1 = gc.createCompatibleImage(width, height, Transparency.OPAQUE);        

        repaintBuffer1 = true;
    }

    @Override
    protected void paintComponent(Graphics g) {
        //super.paintComponent(g);
        int width = this.getWidth();
        int height = this.getHeight();

        if (activeRedraw) { 
            if (repaintBuffer1) {
                Graphics g1 = buffer1.getGraphics();
                g1.clearRect(0, 0, width, height);
                g1.setColor(Color.green);
                g1.drawRect(0, 0, width - 1, height - 1);
                g.drawImage(buffer1, 0, 0, null);
                repaintBuffer1 = false;
            }

            double time = 2* Math.PI * (System.currentTimeMillis() % 5000) / 5000.;
            g.setColor(Color.RED);
            if (rect != null) {
                g.drawImage(buffer1, rect.x, rect.y, rect.x + rect.width, rect.y + rect.height, rect.x, rect.y, rect.x + rect.width, rect.y + rect.height, this);
            }
            rect = new Rectangle((int)(Math.sin(time) * width/3 + width/2 - 20), (int)(Math.cos(time) * height/3 + height/2) - 20, 40, 40);
            g.fillRect(rect.x, rect.y, rect.width, rect.height);

            activeRedraw = false;
        }
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        activeRedraw = true;
        this.repaint();
    }

    @Override
    public void componentHidden(ComponentEvent arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void componentMoved(ComponentEvent arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void componentResized(ComponentEvent e) {
        int width = e.getComponent().getWidth() - (insets.left + insets.right);
        int height = e.getComponent().getHeight() - (insets.top + insets.bottom);
        this.setSize(width, height);
        createBuffers();
    }

    @Override
    public void componentShown(ComponentEvent arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void mouseClicked(MouseEvent e) {
        JTextField field = new JTextField("test");
        field.setBounds(new Rectangle(e.getX(), e.getY(), 100, 20));
        this.add(field);
        repaintBuffer1 = true;
    }

    @Override
    public void mouseEntered(MouseEvent arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void mouseExited(MouseEvent arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void mousePressed(MouseEvent arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void mouseReleased(MouseEvent arg0) {
        // TODO Auto-generated method stub

    }
}