不移动鼠标光标时Java动画会断断续续

问题描述

我有一个非常简单的动画，一个大字体的文字连续（逐个像素）向左移动。首先将文本转换为图像，然后启动计时器任务，重复（每10-20毫秒）将图像的x坐标递减1，并进行重绘（）。

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奇怪的行为。在我的电脑上使用nVidia卡，它运行顺畅。在我的Vaio笔记本电脑上，在BeagleBoneBlack和朋友的Mac上，它会严重破坏。它似乎暂停了一段时间，然后跳到左边大约10个像素，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.

在这些系统上动画的事实让我感到震惊如果您不触摸鼠标，仅断断续续。只要您在窗口内移动鼠标光标，无论速度有多慢，或者拖动窗口本身，动画都会非常流畅！

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!

有人可以解释一下吗？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

尝试完成绘制后调用此方法：

Try calling this method when you are done drawing:

 Toolkit.getDefaultToolkit().sync();

这会刷新Linux等系统使用的图形缓冲区。请参阅Javadoc：

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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