JTextFields 在 JPanel 上的活动绘图之上，线程问题

Posted 2023-02-16

【中文标题】JTextFields 在 JPanel 上的活动绘图之上，线程问题

【英文标题】：JTextFields on top of active drawing on JPanel, threading problems

【发布时间】：2011-03-16 10:29:40

【问题描述】：

有没有人尝试过使用 Swing 构建一个适当的多缓冲渲染环境在其之上可以添加 Swing 用户界面元素？

在这种情况下，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，所以我将它渲染到 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 在先前线程here 中给出的示例。

到目前为止一切顺利；动画流畅，CPU占用率低，无闪烁。

然后我将一个 JTextField 添加到 Jpanel（通过单击屏幕上的任何位置），并通过在文本框内单击来关注它。现在每次光标闪烁时清除矩形的先前位置都会失败，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？图像被异步绘制？）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

【参考方案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擦除旧绘图：

@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，在构造函数中设置背景颜色排除了在paintComponent() 中填充面板的需要，而super.paintComponent() 允许文本字段正常工作。如您所见，建议的解决方法很脆弱。相反，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，“它使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) 来排除这种情况。

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://***.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);
        
    

【讨论】：

感谢您的回复。如果你添加 super.paintComponent(g) 并运行我提供的测试应用程序，你会发现很遗憾这不是一个解决方案。 JPanel 的默认paintComponent 方法会清除其背景，这使得必须重新绘制整个背景图像，这主要违背了预渲染背景图像的目的。我有一种预感，应该可以只重绘必要的区域，但看起来，在不同的线程中重绘文本字段而不是重绘导致这些绘图伪影的背景图像存在一些问题..

关于附录：再次感谢您花时间深入研究此内容。我意识到你的观点是正确的，即自动重绘 JTextFields 无法与使用 super.paintComponent(g) 的主动重绘 一起正常工作，这是正确的。尽管如此，使用 super.paintComponent(g) 意味着必须在每个动画帧上重新绘制整个窗口，从而使 cpu 使用取决于窗口大小，这是我想要防止的。所以我的问题得到了回答，但我的问题仍然存在。我会就此发表一篇新文章。

@Mattijs：使用 setOpaque(false) 将避免填充。我更新了示例以显示绘制时间。差异很大，但必须权衡管理更新的努力。

@Mattijs：顺便说一句，我并不是要抢先你提出一个新问题。绘制时间显示可能有助于缩小范围。

@trashgod：感谢有用的补充。这是我的后续，我详细说明了这个测试代码并总结了我的发现：***.com/questions/3289336/…

【参考方案2】：

我找到了解决方法。

我认为正在发生的事情：每当需要更新 JTextfield 时（即每次光标闪烁时），都会调用 JPanel 的重写 paintComponent()，但使用的 Graphics 参数与 repaint() 调用时不同。因此，在每次光标闪烁时，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。

这有意义吗？如果是这样，这不是 Swing 中的一个奇怪的不便吗？

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无需在每一帧上重新绘制整个屏幕区域即可进行主动绘图的方法，这意味着与窗口大小无关的低 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

    

【讨论】：

注意：在 Windows 上，行为再次不同，解决方法不充分。

我已经详细说明了我的回答。