图像双缓冲技术

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




@SuppressWarnings("serial")
public class Example7_6 extends Applet{
    Image myPicture;


    
    /*init()方法中，先定义一个Image对象，并赋予createImage()方法的返回值，接着创建Graphics对象并赋予其图形环境。最后，让Graphics对象调用drawImage()方法显示图像。
由于这里的Graphics对象offScreenGc是非屏幕对象是，小程序窗口不会有图像显示*/
public void init(){


        myPicture = getImage(getCodeBase(),"1.jpg");


        Image offScreenImage = createImage(getSize().width, getSize().height);
        Graphics offScreenGc = offScreenImage.getGraphics();
        offScreenGc.drawImage(myPicture, 10, 10, this);
        new BufferedDemo(myPicture);




            
    }
    /*drawImage()方法的第四个参数是实现ImageObserver接口，在init()方法中，调用drawImage()方法的参数是this，所以小程序要定义imageUpdate()方法*/
    public boolean imageUpdate(Image img, int infoFlg, int x, int y, int w, int h){
        if (infoFlg == ALLBITS){  // 表示图像已全部装入内存
            repaint();
            return false;// 防止线程再次调用imageUpdate()方法
        }
        else
            return true;
    }

}

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


/*程序的执行过程是，当小程序调用drawImage()方法时，drawImage()方法将创建一个调用 imageUpdate()方法的线程，在imageUpdate()方法中，测定图像是否已在部分调入内存。创建的线程不断调用imageUpdate()方法，直到该方法返回false为止。参数infoFlg使小程序能知道图像装入内存的情况。当infoFlg等于ALLBITS时，表示图像已全部装入内存。当该方法发现图像已全部装入内存后，置imageLoaded为真，并调用repaint()方法重画小程序窗口。方法返回false防止线程再次调用imageUpdate()方法。*/
@SuppressWarnings("serial")
class BufferedDemo extends JFrame{
    public BufferedDemo(Image img){
        this.getContentPane().add(new PicPanel(img));
        setTitle("双缓技术演示");
        setSize(300, 300);
        setVisible(true);
    }
}

import java.awt.Color;
import java.awt.Cursor;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.image.BufferedImage;


import javax.swing.JPanel;


@SuppressWarnings("serial")
class PicPanel extends JPanel implements MouseListener, MouseMotionListener{
    int x = 0, y = 0, dx = 0, dy = 0;
    BufferedImage bimg1, bimg2;
    boolean upstate = true;
    public PicPanel(Image img){
        this.setBackground(Color.white);
        this.addMouseListener(this);
        this.addMouseMotionListener(this);
        bimg1 = new BufferedImage(img.getWidth(this), img.getHeight(this),BufferedImage.TYPE_INT_ARGB);
        bimg2 = new BufferedImage(img.getWidth(this), img.getHeight(this),BufferedImage.TYPE_INT_ARGB);
        Graphics2D g2D1 = bimg1.createGraphics();
        Graphics2D g2D2 = bimg2.createGraphics();
        g2D1.drawImage(img, 0, 0, this);
        g2D2.drawImage(img, 0, 0, this);
        g2D2.drawRect(1, 1, img.getWidth(this) - 3, img.getHeight(this) - 3);
    }
    public void paintComponent(Graphics g){
        super.paintComponent(g);
        Graphics2D g2D = (Graphics2D)g;
        if (upstate)
            g2D.drawImage(bimg1, x, y, this);
        else
            g2D.drawImage(bimg2,x, y, this);
    }
    public void mousePressed(MouseEvent e){
        if (e.getX() >= x && e.getX() < x + bimg1.getWidth(this) && e.getY() >= y&& e.getY() < y + bimg1.getHeight(this)){
            upstate = false;
            setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR));
            dx = e.getX() - x;
            dy = e.getY() - y;
            repaint();
        }
    }
    public void mouseExited(MouseEvent e){}
    public void mouseClicked(MouseEvent e){}
    public void mouseEntered(MouseEvent e){}
    public void mouseReleased(MouseEvent e){
        this.setCursor(Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
        upstate = true;
        repaint();
    }
    public void mouseMoved(MouseEvent e){}
    public void mouseDragged(MouseEvent e){
        if (!upstate){
            x = e.getX() - dx;
            y = e.getY() - dy;
            repaint();
        }


    }
}