java绘制组件绘制两次

Question

据我所知，Swing将决定何时需要重新绘制，这将解释paintComponent()执行两次的原因。但我已经制作了一个应用程序，可以休眠16毫秒、重新绘制、休眠16毫秒、重新绘制、休眠16毫秒，等等：

while(true)
{
    frame.repaint();
    try{Thread.sleep(16)}catch(Exception e){}
}

它应该以每秒60帧的速度工作。但是，FPS测量程序（如FRAP）显示应用程序以120fps的速度运行。所以基本上，应用程序所做的是：画框，画框，睡眠，画框，画框，睡眠。。。如何让swing为每个repaint()调用绘制一个帧？（哦，我试着用Timer代替sleep()，结果是一样的）

下面是在Oracle教程中找到的SwingPaintDemo示例。我添加了一个while循环，它将每16毫秒重新绘制一次。我还将undecorated设置为true（这是FRAPS显示每秒实际帧数的唯一方法）

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

/*
 ***************************************************************
 * Silly Sample program which demonstrates the basic paint
 * mechanism for Swing components.
 ***************************************************************
 */
public class SwingPaintDemo {

    public static void main(String[] args) {
        JFrame f = new JFrame("Aim For the Center");
        f.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
        Container panel = new BullsEyePanel();
        panel.add(new JLabel("BullsEye!", SwingConstants.CENTER), BorderLayout.CENTER);
        f.setUndecorated(true);
        f.setSize(200, 200);
        f.getContentPane().add(panel, BorderLayout.CENTER);
        f.show();

        while(true)
        {
            f.repaint();
            try{Thread.sleep(16);}catch(Exception e){}
        }
    }
}

/**
 * A Swing container that renders a bullseye background
 * where the area around the bullseye is transparent.
 */
class BullsEyePanel extends JPanel {

    public BullsEyePanel() {
        super();
        setOpaque(false); // we don't paint all our bits
        setLayout(new BorderLayout());
        setBorder(BorderFactory.createLineBorder(Color.black));
    }

    public Dimension getPreferredSize() {
        // Figure out what the layout manager needs and
        // then add 100 to the largest of the dimensions
        // in order to enforce a 'round' bullseye 
        Dimension layoutSize = super.getPreferredSize();
        int max = Math.max(layoutSize.width,layoutSize.height);
        return new Dimension(max+100,max+100);
    }

    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Dimension size = getSize();
        int x = 0;
        int y = 0;
        int i = 0;
        while(x < size.width && y < size.height) {
            g.setColor(i%2==0? Color.red : Color.white);
            g.fillOval(x,y,size.width-(2*x),size.height-(2*y));
            x+=10; y+=10; i++;
        }
    }
}

Answer 1

1）基本上，paintComponent()内的方法不需要调用repaint()

2）当需要重新绘制时，Swing GUI会自动调用paintComponent()

3）对于今天使用Graphics(2D)的Swing GUI，默认情况下使用Swing Timer

4）为frame.repaint();调用重复repaint的代码，删除该

5）frame.repaint();是一种有用的方法，如果您add/remove/modify已经可见

你是说

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class SwingPaintDemo {

    public static void main(String[] args) {
        JFrame f = new JFrame("Aim For the Center");
        f.addWindowListener(new WindowAdapter() {

            @Override
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
        Container panel = new BullsEyePanel();
        panel.add(new JLabel("BullsEye!", SwingConstants.CENTER), BorderLayout.CENTER);
        f.getContentPane().add(panel, BorderLayout.CENTER);
        f.pack();
        f.setVisible(true);
    }
}

/**
 * A Swing container that renders a bullseye background
 * where the area around the bullseye is transparent.
 */
class BullsEyePanel extends JPanel {

    public BullsEyePanel() {
        super();
        setOpaque(false); // we don't paint all our bits
        setLayout(new BorderLayout());
        setBorder(BorderFactory.createLineBorder(Color.black));
    }

    @Override
    public Dimension getPreferredSize() {
        // Figure out what the layout manager needs and
        // then add 100 to the largest of the dimensions
        // in order to enforce a 'round' bullseye
        Dimension layoutSize = super.getPreferredSize();
        int max = Math.max(layoutSize.width, layoutSize.height);
        return new Dimension(max + 100, max + 100);
    }

    @Override
    protected void paintComponent(Graphics g) {
        Dimension size = getSize();
        int x = 0;
        int y = 0;
        int i = 0;
        while (x < size.width && y < size.height) {
            g.setColor(i % 2 == 0 ? Color.red : Color.white);
            g.fillOval(x, y, size.width - (2 * x), size.height - (2 * y));
            x += 10;
            y += 10;
            i++;
        }
    }
}

编辑，你上一个问题中链接的@trashgod代码有什么问题，关于JPanel's repaint（this.repaint()）

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.util.Random;
import javax.swing.*;

/** @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 static final long serialVersionUID = 1L;
    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);
        }
    }
}