不移动鼠标光标时，Java 动画卡顿 [英] Java animation stutters when not moving mouse cursor

问题描述

我有一个非常简单的动画，一个大字体的文本向左连续(逐像素)移动.首先将文本转换为图像，然后启动一个计时器任务，该任务重复(每 10-20 毫秒)将图像的 x 坐标减 1，并执行 repaint().

I have a quite simple animation, a text in a big font moving continuously (pixel by pixel) to the left. The text is first converted to an image, then a timer task is started which repeatedly (every 10-20 ms) decrements the x coordinate of the image by 1, and does a repaint().

此程序在某些系统上显示出奇怪的行为.在我的带有 nVidia 卡的 PC 上，它运行流畅.在我的 Vaio 笔记本、BeagleBoneBlack 和朋友的 Mac 上，它严重卡顿.似乎暂停了一会儿，然后向左跳了大约 10 个像素，然后再次暂停，依此类推.

This program shows a strange behavior on some systems. On my PC with a nVidia card it runs smoothly. On my Vaio notebook, on a BeagleBoneBlack and on a friend's Mac it stutters heavily. It appears to pause for a while, then jump to the left about 10 pixels, pause again and so on.

让我感到难堪的是，在这些系统上，如果您不触摸鼠标，动画只有会断断续续.只要你在窗口内移动鼠标光标，无论多慢，或者拖动窗口本身，动画运行得非常流畅！

What stumps me is the fact that on these systems the animation only stutters if you don't touch the mouse. As long as you move the mouse cursor within the window, no matter how slowly, or drag the window itself around, the animation runs perfectly smooth!

谁能解释一下?这是程序:

Can anybody explain this? Here is the program:

import java.awt.*;
import java.awt.image.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
import java.util.*;

class Textimg extends JComponent
{
    String      str;
    Font        font;
    int         x = 0;
    final int   ytext = 136;
    Image       img;

    public Textimg(String s)
    {
        str = s;
        font = new Font("Noserif", Font.PLAIN, 96);
        setLayout(null);
    }

    protected void paintComponent(Graphics g)
    {
        if (img == null)
        {
            img = createImage(4800, 272);
            Graphics gr = img.getGraphics();

            gr.setFont(font);
            gr.setColor(Color.BLACK);
            gr.fillRect(0, 0, 4800, 272);
            gr.setColor(new Color(135, 175, 0));
            gr.drawString(str, 0, ytext);
            gr.dispose();
        }

        g.drawImage(img, x, 0, this);
    }

    public void addX(int dif)
    {
        if (isVisible())
        {
            x = x + dif;

            Graphics g = getGraphics();

            if (g != null) paintComponent(g);
        }
    }
} 


public class Banner extends JFrame 
{ 
    StringBuffer    buf;
    int             sleeptime = 10;

    Banner(String path) throws IOException 
    { 
        setSize(new Dimension(480, 272));
        setTitle("Java Test");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLayout(null);

        BufferedReader reader = new BufferedReader(
                new InputStreamReader(new FileInputStream(path), "UTF-8"));

        buf = new StringBuffer();

        while (true) 
        {
           String line = reader.readLine();

           if (line == null) break;
           buf.append(line);
        }

        final Textimg textimg = new Textimg(buf.toString());

        add(textimg);
        textimg.setBounds(0, 0, 480, 272);

        final javax.swing.Timer timer = new javax.swing.Timer(200, new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
                textimg.addX(-1);
            }
        });

        timer.setDelay(sleeptime);
        timer.start();
    }

    //----------------------------------------------------------------------

    public static void main(String[] args) throws Exception
    {
        new Banner(args[0]).setVisible(true);
    }
}

推荐答案

绘制完成后尝试调用此方法:

Try calling this method when you are done drawing:

 Toolkit.getDefaultToolkit().sync();

这会刷新某些系统(如 Linux)使用的图形缓冲区.请参阅 Javadoc:http://docs.oracle.com/javase/7/docs/api/java/awt/Toolkit.html#sync()

This flushs the graphics buffer which some systems like Linux use. See the Javadoc: http://docs.oracle.com/javase/7/docs/api/java/awt/Toolkit.html#sync()

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