——求助：drawPolygon的问题，总是显示不出来想要的效果————

Question

本帖最后由 songhu987 于 2011-05-16 16:06:08 编辑

Answer 1

你的错误原因，见我添加上去的三行注释import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;import javax.swing.JFrame;
import javax.swing.JPanel;public class drawPolygon {    public static void main(String[] args) {        // 测试坐标数据,将x、y轴坐标分别存储   
        int xpoints[] = {25, 145, 25, 145, 275, 478, 345};
        int ypoints[] = {25, 25, 145, 145, 165, 223, 267};
        int npoints = 7;
        //你帖出来的程序是错误的，你PolygonFrame的构造函数的contentPane.add(panel);
        //你哪来的panel
        //我改了一个，把panel作为参数传递进去
        myPolygonPanel panel = new myPolygonPanel();
        PolygonFrame frame = new PolygonFrame(panel);
        panel.setPoints(xpoints, ypoints, npoints);
//  Container contentPane = getContentPane();   
//  contentPane.add(panel);    
        frame.show();
    }
}class PolygonFrame extends JFrame {    public PolygonFrame(JPanel panel) {
        setTitle(" Polygon ");
        setResizable(false);
        setSize(600, 400);
        Container contentPane = getContentPane();
        contentPane.add(panel);
    }
}class myPolygonPanel extends JPanel {    int[] xpoints;
    int[] ypoints;
    int npoints;    // 设置坐标参数   
    public void setPoints(int[] x, int[] y, int n) {
        this.xpoints = x;
        this.ypoints = y;
        this.npoints = n;
    }    // 画多边形   
    public void paint(Graphics g) {
        g.setColor(Color.red);
        g.drawPolygon(xpoints, ypoints, npoints); // 首尾相接   
        // g.drawPolyline(xpoints, ypoints, npoints); //首尾未相接   
    }
}  

Answer 2

当时确实是没看出来，也没有想到是这个原因，谢谢wenbodong。第二个小问题是，怎样才能想把先后画出的两个文件的图形同时显示出来？ 以及图形的缩放？能给个简单小例子最好

Answer 3

什么是先后画出的两个“文件”图形同时显示？不太清楚你的意思。
至于缩放变换，就是对BufferedImage进行变换嘛。不知道你是否熟悉BufferedImage，用getRGB可以获取它的一个数组，这就是它图像的内容，对此进行操作。不过，Java已经为你提供了强大的图形变换类，不用自己设计了。
下面是一个演示，程序运行时点击菜单打开一个图片文件，调节滑块可进行缩放。作为一个示例程序，稍微长了一点，你主要是看change2这个函数，再看看pan中的paint就可以了。/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 *//**
 *
 * @author Administrator
 */
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.*;
import java.awt.*;
import java.awt.geom.*;
import java.awt.image.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.util.*;
import javax.imageio.ImageIO;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
public class ZoomInAndZoomOut {
    JFrame frame;
    JPanel pan;
    JPanel contentPane;
    JMenuBar menuBar;
    JMenu fileMenu;
    JMenuItem openMenuItem;
    JScrollPane jsp;
    BufferedImage buffer,paintBuffer;
    JSlider opaqueSlider;
    double opaqueValue;
    public ZoomInAndZoomOut(){
        //takePhoto();
        frame=new JFrame();
        pan=new JPanel(){
            public void paint(Graphics g){
                int width=pan.getWidth();
                int height=pan.getHeight();
                g.setColor(Color.WHITE);
                g.fillRect(0, 0, width, height);
                if(paintBuffer!=null){
                    g.drawImage(paintBuffer, 0, 0, null);
                }
            }
        };
        pan.addMouseListener(new MouseAdapter(){
            public void mousePressed(MouseEvent e){
                int x=e.getX();
                int y=e.getY();
                System.out.println("["+x+","+y+"]");
            }
        });
        pan.setPreferredSize(new Dimension(800,600));
        contentPane=new JPanel();
        contentPane.setLayout(new BorderLayout());
        setMenu();
        jsp=new JScrollPane(pan);
        jsp.setPreferredSize(new Dimension(800,600));
        contentPane.add(jsp,BorderLayout.CENTER);
        setSlider();
        frame.setContentPane(contentPane);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setVisible(true);
    }
    public void setMenu(){
        menuBar=new JMenuBar();
        contentPane.add(menuBar,BorderLayout.NORTH);
        fileMenu=new JMenu("文件");
        menuBar.add(fileMenu);
        openMenuItem=new JMenuItem("打开");
        openMenuItem.addActionListener(new ActionListener(){
           public void actionPerformed(ActionEvent e) {
               JFileChooser jfc=new JFileChooser();
               jfc.setCurrentDirectory(new File("."));
               jfc.setApproveButtonText("确定");
               int result=jfc.showOpenDialog(frame);
               if(result==JFileChooser.APPROVE_OPTION){
                   File f=jfc.getSelectedFile();
                    try {
                        buffer = ImageIO.read(f);
                        paintBuffer = ImageIO.read(f);
                        frame.repaint();
                    } catch (IOException ex) {
                        Logger.getLogger(ZoomInAndZoomOut.class.getName()).log(Level.SEVERE, null, ex);
                    }
               }
           }
        });
        fileMenu.add(openMenuItem);
    }
    public void setSlider(){
        opaqueSlider=new JSlider();
        opaqueSlider.setMinimum(0);
        opaqueSlider.setMaximum(200);
        opaqueSlider.setMajorTickSpacing(10);
        opaqueSlider.setMinorTickSpacing(2);
        opaqueSlider.setPaintLabels(true);
        opaqueSlider.setPaintTrack(true);
        opaqueSlider.setPaintTicks(true);
        opaqueSlider.setValue(100);
        opaqueValue=1;
        opaqueSlider.addChangeListener(new ChangeListener(){
            public void stateChanged(ChangeEvent e){
                opaqueValue=opaqueSlider.getValue()/100.0;
                change2(opaqueValue);
                int width=(int)(buffer.getWidth()*opaqueValue);
                int height=(int)(buffer.getHeight()*opaqueValue);
                pan.setPreferredSize(new Dimension(width,height));
                jsp.updateUI();
                frame.repaint();
                System.out.println(opaqueValue);
            }
        });
        contentPane.add(opaqueSlider,BorderLayout.SOUTH);
    }
    public void change2(double rate){
        //生成一个缩放变换，两个参数分别是X轴、Y轴的缩放因子
        AffineTransform transform = AffineTransform.getScaleInstance(rate,rate);
        //构造线性映射
        AffineTransformOp op = new AffineTransformOp(transform,AffineTransformOp.TYPE_BILINEAR);
        //进行变换
        paintBuffer=op.filter(buffer, null);
    }
    public static void main(String args[]){
        new ZoomInAndZoomOut();
    }
}对于同时显示两个图片的问题，可以加我QQ：815611030，备注说明：Java