手绘图实例

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package handdraw;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import javax.swing.*;

/**
 *
 * @author 91152
 */
public class HandDraw {

    // 画图区的宽度
	private final int AREA_WIDTH = 500;
	// 画图区的高度
	private final int AREA_HEIGHT = 400;
	// 下面的preX、preY保存了上一次鼠标拖动事件的鼠标坐标
	private int preX = -1;
	private int preY = -1;
	// 定义一个右键菜单用于设置画笔颜色
        JPopupMenu pop = new JPopupMenu();
        JMenuItem redItem = new JMenuItem("红色");
        JMenuItem greenItem = new JMenuItem("绿色");
        JMenuItem blueItem = new JMenuItem("蓝色");
        BufferedImage image = new BufferedImage(AREA_WIDTH,
            AREA_HEIGHT,BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();
        private JFrame jf = new JFrame("简单手绘程序");
        private MyJPanel drawArea = new MyJPanel();
        private Color foreColor = new Color(255,0,0);
        
        public void init(){
            ActionListener menuListener = e ->{
              if(e.getActionCommand().equals("绿色")){
                  foreColor = new Color(0,255,0);
              }  
              if(e.getActionCommand().equals("红色")){
                  foreColor = new Color(255,0,0);
              }
              if(e.getActionCommand().equals("蓝色")){
                  foreColor = new Color(0,0,255);
              }
            };
            redItem.addActionListener(menuListener);
            greenItem.addActionListener(menuListener);
            blueItem.addActionListener(menuListener);
            pop.add(redItem);
            pop.add(greenItem);
            pop.add(blueItem);
            drawArea.add(pop);
            
            g.fillRect(0, 0, AREA_WIDTH, AREA_HEIGHT);
            drawArea.setPreferredSize(new Dimension(AREA_WIDTH,AREA_HEIGHT));
            drawArea.addMouseMotionListener(new MouseMotionAdapter(){
                public void mouseDragged(MouseEvent e){
                    if(preX >0 && preY >0){
                        g.setColor(foreColor);
                        //这个设计很精巧
                        g.drawLine(preX,preY,e.getX(),e.getY());
                    }
                    preX = e.getX();
                    preY = e.getY();
                    drawArea.repaint();
                }
            });
            drawArea.addMouseListener(new MouseAdapter(){
                public void mouseReleased(MouseEvent e){
                    if(e.isPopupTrigger()){
                        pop.show(drawArea, e.getX(), e.getY());
                    }
                    preX=-1;
                    preY = -1;
                }
            });
            jf.add(drawArea);
            jf.pack();
            jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            jf.setLocationRelativeTo(null);
            jf.setVisible(true);
            
        }
        
    public static void main(String[] args) {
        new HandDraw().init();
    }
    
    class MyJPanel extends JPanel{
        @Override
        public void paint(Graphics g){
            //super.paint(g);
            g.drawImage(image, 0, 0, null);
        }
    }
    
}