[原创]利用橡皮条技术画图

[原创]利用橡皮条技术画图

在进行有绘制图形功能的软件开发中都会面临橡皮条技术，所谓橡皮条技术就是在绘制过程中出现鼠标移动的记录，当鼠标松开时绘制完整的图形。下面给出一个简单的橡皮条技术的应用，该应用是在APPLET上绘制一个矩形，并且只能绘制一个矩形，这对于图象裁剪很有帮助：

/**
 * @(#) xortest.java
 *
 * Copyright 2004 Opensource Develop Team. All rights reserved.
 */
import java.applet.Applet;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;

/**
 * 在APPLET上绘制一个矩形，当要进行第二次绘制时，上次绘制的矩形消失。
 * @author ODT
 * @see java.applet.Applet
 * @since JDK 1.3
 * @version 1.0 07/05/2004
 */
public class xortest extends Applet
{
     Point pressed, last; // 记录图形起点和鼠标不停移动时终点坐标
     boolean firstRect; // 只画一个矩形

     public void init()
     {
           addMouseListener(new MouseAdapter()
           {
                 public void mousePressed(MouseEvent e)
                 {
                       firstRect = true; // 确保一个矩形
                       pressed = e.getPoint(); // 获得起点坐标
                 }

                 public void mouseReleased(MouseEvent e)
                 {
                       if (pressed != null)
                       {
                             Point released = e.getPoint();
                             Rectangle clip = new Rectangle(); // clip为最终确定的矩形
                             Graphics g = getGraphics();
                             Dimension size = getSize();

                             try
                             {
                                   clip.x = pressed.x;
                                   clip.y = pressed.y;
                                   clip.width = Math.abs(released.x - pressed.x);
                                   clip.height = Math.abs(released.y - pressed.y);

                                   g.clearRect(0, 0, size.width, size.height);
                                   g.drawRect(clip.x,  clip.y, clip.width, clip.height); // 画最后的矩形
                             }
                             finally
                             {
                                   g.dispose();
                             }
                       }
                 }

                 public void mouseClicked(MouseEvent e)
                 {
                       repaint();
                 }
           });

           addMouseMotionListener(new MouseMotionAdapter()
           {
                 public void mouseDragged(MouseEvent e)
                 {
                       Point loc = e.getPoint(); // 鼠标当前位置
                       Graphics g = getGraphics();

                       try
                       {
                             g.setXORMode(getBackground()); // 设置绘图模式为XOR，橡皮条颜色为背景灰色
                             if (firstRect)
                             {
                                   firstRect = false; // 如果有矩形的画则设置为FALSE
                             }
                             else
                             {
                                   g.drawRect(pressed.x,  pressed.y,
                                           Math.abs(pressed.x - last.x),
                                           Math.abs(pressed.y - last.y));
                             }
                             g.drawRect(pressed.x,  pressed.y,
                                     Math.abs(loc.x - pressed.x),
                                     Math.abs(loc.y - pressed.y));
                             last = e.getPoint();
                       }
                       finally
                       {
                             g.dispose();
                       }
                 }
           });
     }
}

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