在Java中的线绘图

问题描述

这段代码有许多问题

  public class LineEx extends JFrame implements MouseMotionListener，MouseListener {
 int X1，Y1，X2，Y2; 
 public LineEx（）{
 JLabel image = new JLabel（）; 
 JFileChooser chooser = new JFileChooser（）; 
 
 chooser.setCurrentDirectory（new File（。））; 
 int r = chooser.showOpenDialog（new JFrame（））; 
文件文件= chooser.getSelectedFile（）; 
 if（r == JFileChooser.APPROVE_OPTION）{
 try {
 BufferedImage bf; 
 bf = ImageIO.read（file）; 
 ImageIcon icon = new ImageIcon（bf）; 
 image.setIcon（icon）; 
 image.setHorizo​​ntalAlignment（JLabel.CENTER）; 
 $ b $ catch（IOException ex）{
 Logger.getLogger（LineEx.class.getName（））.log（Level.SEVERE，null，ex）; 
} 
} 
 JScrollPane jsp = new JScrollPane（image）; 
 getContentPane（）。add（jsp）; 
 image.addMouseListener（this）; 
 image.addMouseMotionListener（this）; 
 this.pack（）; 
} 
 public static void main（String ar []）{
 LineEx line = new LineEx（）; 
 line.setVisible（true）; 
 line.setDefaultCloseOperation（EXIT_ON_CLOSE）; 
} 
 
 public void mouseClicked（MouseEvent e）{
 
} 
 
 public void mousePressed（MouseEvent e）{
 X1 = e.getX（）; 
 y1 = e.getY（）; 
 
 
 public void mouseReleased（MouseEvent e）{
 JOptionPane.showMessageDialog（rootPane，X1 =+ x1 +Y1 =+ y1）; 
} 
 
 public void mouseEntered（MouseEvent e）{
} 
 
 public void mouseExited（MouseEvent e）{
} 
 @Override 
 public void paint（Graphics g）{
 super.paintComponents（g）; 
 Graphics2D gd =（Graphics2D）g; 
 gd.setRenderingHint（RenderingHints.KEY_ANTIALIASING，RenderingHints.VALUE_ANTIALIAS_ON）; 
 Line2D line = new Line2D.Double（x1，y1，x2，y2）; 
 gd.draw（line）; 
} 
 
 public void mouseDragged（MouseEvent e）{
 x2 = e.getX（）; 
 y2 = e.getY（）; 
 repaint（）; 
} 
 
 public void mouseMoved（MouseEvent e）{
} 
} 
  

1. MouseEvents没有得到确切的坐标，这意味着每当我画一条线时它都不在其位置上。这背后的原因是什么？


2. 当滚动条上下移动时，我想沿图像移动一行，我该怎么做？

>

解决方案

• MouseEvents没有得到确切的坐标，这意味着每当我画一个它不在它的位置上。这背后的原因是什么？

当滚动条上下移动时，我想沿着图像移动线条，我该怎么做？ >

您从 JLabel 中获得了正确的坐标，但在的JFrame 。框架坐标从左上角开始，包含窗口标题/边框。

覆盖 paintComponent 方法放在 JLabel 上，它会得到正确的插入和坐标。

---

$ b

 类ImageComponent继承JComponent 
实现MouseListener，MouseMotionListener {
 private final BufferedImage img; 
私人点p1，p2; 
 
 public ImageComponent（URL url）抛出IOException {
 img = ImageIO.read（url）; 
 setPreferredSize（new Dimension（img.getWidth（），img.getHeight（）））; 
 addMouseListener（this）; 
 addMouseMotionListener（this）; 
} 
 @Override protected void paintComponent（Graphics g）{
 super.paintComponent（g）; 
 g.drawImage（img，0，0，img.getWidth（），img.getHeight（），this）; 
 if（p1！= null&& p2！= null）
 g.drawLine（p1.x，p1.y，p2.x，p2.y）; 
} 
 @Override public void mousePressed（MouseEvent e）{
 p1 = e.getPoint（）; 
} 
 @Override public void mouseDragged（MouseEvent e）{
 mouseReleased（e）; 
} 
 @Override public void mouseReleased（MouseEvent e）{
 p2 = e.getPoint（）; 
 repaint（）; 
} 
 @Override public void mouseMoved（MouseEvent e）{} 
 @Override public void mouseClicked（MouseEvent e）{} 
 @Override public void mouseEntered（MouseEvent e）{} 
 @Override public void mouseExited（MouseEvent e）{} 
} 
  

测试代码（生成此截图）：

  public static void main（String [] args）throws Exception {
 
最终网址lenna = 
新网址（http://upload.wikimedia.org/wikipedia/en/2/24/Lenna.png）; 
 
 final ImageComponent image = new ImageComponent（lenna）; 
 
 JFrame frame = new JFrame（Test）; 
 frame.add（new JScrollPane（image））; 
 
 frame.setDefaultCloseOperation（JFrame.EXIT_ON_CLOSE）; 
 frame.setSize（400，300）; 
 frame.setVisible（true）; 
} 
  

There are number of problems with this code

public class LineEx extends JFrame implements MouseMotionListener,MouseListener{
    int x1,y1,x2,y2;
    public LineEx(){
        JLabel image=new JLabel("");
        JFileChooser chooser=new JFileChooser();

        chooser.setCurrentDirectory(new File("."));
        int r=chooser.showOpenDialog(new JFrame());
        File file=chooser.getSelectedFile();
        if(r==JFileChooser.APPROVE_OPTION){
            try {
                BufferedImage bf;
                bf = ImageIO.read(file);
                ImageIcon icon=new ImageIcon(bf);
                image.setIcon(icon);
                image.setHorizontalAlignment(JLabel.CENTER);

            } catch (IOException ex) {
                Logger.getLogger(LineEx.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
        JScrollPane jsp=new JScrollPane(image);
        getContentPane().add(jsp);
        image.addMouseListener(this);
        image.addMouseMotionListener(this);
        this.pack();
    }
    public static void main(String ar[]){
        LineEx line=new LineEx();
        line.setVisible(true);
        line.setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    public void mouseClicked(MouseEvent e) {

    }

    public void mousePressed(MouseEvent e) {
        x1=e.getX();
        y1=e.getY();
    }

    public void mouseReleased(MouseEvent e) {
        JOptionPane.showMessageDialog(rootPane, "X1="+x1+"  Y1="+y1);
    }

    public void mouseEntered(MouseEvent e) {
    }

    public void mouseExited(MouseEvent e) {
    }
    @Override
    public void paint(Graphics g){
        super.paintComponents(g);
        Graphics2D gd=(Graphics2D)g;
        gd.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        Line2D line=new Line2D.Double(x1,y1,x2,y2);
        gd.draw(line);
    }

    public void mouseDragged(MouseEvent e) {
        x2=e.getX();
        y2=e.getY();
        repaint();
    }

    public void mouseMoved(MouseEvent e) {
    }
}

1. MouseEvents are not getting exact co-ordinates that means whenever i draw a line it is not on its position. What is the reason behind this?
2. I want to move line along the image when scrollbar goes up and down, how can i do that?

解决方案

You are getting the correct coordinates from the JLabel but paints on the JFrame. And the frame coordinates begins at the top left point and "includes" the window title/border.

Override the paintComponent method on the JLabel and it you will get the correct insets and coordinates.

---

Example:

class ImageComponent extends JComponent
        implements MouseListener, MouseMotionListener {
    private final BufferedImage img;
    private Point p1, p2;

    public ImageComponent(URL url) throws IOException {
        img = ImageIO.read(url);
        setPreferredSize(new Dimension(img.getWidth(), img.getHeight()));
        addMouseListener(this);
        addMouseMotionListener(this);
    }
    @Override protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(img, 0, 0, img.getWidth(), img.getHeight(), this);
        if (p1 != null && p2 != null)
            g.drawLine(p1.x, p1.y, p2.x, p2.y);
    }
    @Override public void mousePressed(MouseEvent e) {
        p1 = e.getPoint();
    }
    @Override public void mouseDragged(MouseEvent e) {
        mouseReleased(e);
    }
    @Override public void mouseReleased(MouseEvent e) {
        p2 = e.getPoint();
        repaint();
    }
    @Override public void mouseMoved(MouseEvent e) {}
    @Override public void mouseClicked(MouseEvent e) {}
    @Override public void mouseEntered(MouseEvent e) {}
    @Override public void mouseExited(MouseEvent e) {}
}

Test code (generates this screenshot):

public static void main(String[] args) throws Exception {

    final URL lenna =
        new URL("http://upload.wikimedia.org/wikipedia/en/2/24/Lenna.png");

    final ImageComponent image = new ImageComponent(lenna);

    JFrame frame = new JFrame("Test");
    frame.add(new JScrollPane(image));

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(400, 300);
    frame.setVisible(true);
}

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