usedoublebuffering.java

《java游戏设计》范例源代码及程序执行结果

// 程序：使用双缓冲区
// 范例文件：UseDoubleBuffering.java

import java.awt.*;
import java.applet.*;

public class UseDoubleBuffering extends Applet implements Runnable
{
   int    X,Y,moveX,moveY,width,height;  
   Thread newThread;                      //新线程

   Image    OffScreen;                    //次画面
   Graphics drawOffScreen;                //绘制次画面的Graphics实体

   public void init()
   {
      X      = 0;                         //X坐标
      Y      = 0;                         //Y坐标
      moveX  = 2;                         //X轴移动距离
      moveY  = 3;                         //Y轴移动距离
      width  = getSize().width;           //Applet的宽度
      height = getSize().height;          //Applet的高度

      OffScreen     = createImage(width,height); //建立次画面
      drawOffScreen = OffScreen.getGraphics();   //取得次画面的绘制类
   }

   public void start()                    //start()函数  
   {
      newThread = new Thread(this);       //建立与启动新线程
      newThread.start();
   }

   public void stop()                     //stop()函数
   {
      newThread = null;                   //将线程设为null
   }

   public void paint(Graphics g)
   {
      //下面这两行的作用为清除次画面
      drawOffScreen.setColor(Color.black);
      drawOffScreen.fillRect(0,0,width,height);

      //下面这两行的作用为在次画面上绘制实心正圆形
      drawOffScreen.setColor(Color.white);
      drawOffScreen.fillOval(X,Y,30,30);  

      //将次画面贴到主画面上
      g.drawImage(OffScreen,0,0,this); 
   }

   public void update(Graphics g)         //update()函数
   {
      paint(g);                           //只单纯调用paint()函数
   }

   public void run()
   {
      while(newThread != null)            //动画循环
      {
         repaint();                       //重新绘制图像

         try
         {
            Thread.sleep(50);             //暂停程序执行50毫秒
         }
         catch(InterruptedException E){ }
       
         X = X + moveX;                   //计算新的X坐标
         Y = Y + moveY;                   //计算新的Y坐标
    
         //碰撞到边界时就会反弹
         if(X >= (width - 30))
         {
            X     = width - 30;
            moveX = -moveX;
         }
         if(X <= 0)
         {
            X = 0;
            moveX = -moveX;
         } 
         if(Y >= (height - 30))
         {
            Y     = height - 30;
            moveY = -moveY;
         }
         if(Y <= 0)
         {
            Y = 0;
            moveY = -moveY;
         } 
      }
   }
}