The best way to make zoom over a Graphic2D object

Question

Hi to all!
I'm reading severals webs that describe the way to make zoom using Java2D. I'm working with an object Graphic2D and I want let the user to zomming in over the image, clicking the left mouse button and make zoom out clicking the right mouse button. I'm trying to make this using the method "scale()" of Graphic2D class, but I don't understand how it really works and I don't know if I have choised the best way to implement the zoom function. I let you a piece of code that I think sould do that I have said, why doesn't it works?
public class zoom extends JPanel implements MouseListener, MouseMotionListener{
    public static JFrame window = new JFrame();
    Graphics2D g2;
    public static void main(String[] args) {
        zoom internalPanel = new zoom();
        internalPanel.setBorder(BorderFactory.createTitledBorder("Zoom test"));
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setPreferredSize(new Dimension(500, 500));
        window.setLayout(new FlowLayout(FlowLayout.CENTER));
        window.add(internalPanel);
        window.pack();
        window.setVisible(true);
    public zoom(){  
        setPreferredSize(new Dimension(500, 500));
        addMouseListener(this);
        addMouseMotionListener(this);
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g2 = (Graphics2D) g;
        Dimension d = getSize();
        Image mImagen = createImage(500, 500);
        Graphics2D offG = (Graphics2D) mImagen.getGraphics();
        offG.setColor(Color.white);
        offG.fill(new Rectangle2D.Double(0, 0, d.width, d.height));
        g2.drawImage(mImagen, 0, 20, null);
        g2.setColor(Color.blue);
        Ellipse2D ellipse = new Ellipse2D.Double(100.0d, 100.0d, 100.0d, 100.0d);
        g2.fill(ellipse);
    public void mouseClicked(MouseEvent e) {
        if (e.getButton()==1){
            g2.scale(10.0, 10.0);
        if (e.getButton()==3){
            g2.scale(-10.0, -10.0);
    public void mousePressed(MouseEvent e){}
    public void mouseReleased(MouseEvent e){}
    public void mouseEntered(MouseEvent e){}
    public void mouseExited(MouseEvent e){}
    public void mouseDragged(MouseEvent e){}
    public void mouseMoved(MouseEvent e){}
}Thanks for read.
Edited by: Daniel.GB on May 1, 2008 5:02 PM

Answer 1

zoom makes centering the zoomed image over the mouse pointer
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
public class ZoomTest2 extends JPanel implements MouseListener,
                                                 MouseMotionListener {
    Image mImagen;
    Point loc;
    double scale = 1.0;
    double scaleInc = 0.1;
    double MIN_SCALE = 0.25;
    final int WIDTH  = 500;
    final int HEIGHT = 500;
    public ZoomTest2(){  
        addMouseListener(this);
        addMouseMotionListener(this);
    public Dimension getPreferredSize() {
        Dimension d = new Dimension();
        d.width  = (int)(scale*WIDTH);
        d.height = (int)(scale*HEIGHT);
        return d;
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        Dimension d = getSize();
        if(mImagen == null) {
            mImagen = createImage(WIDTH, HEIGHT);
            Graphics2D offG = (Graphics2D) mImagen.getGraphics();
            offG.setColor(Color.white);
            offG.fill(new Rectangle2D.Double(0, 0, d.width, d.height));
            offG.dispose();
            loc = new Point(WIDTH/2, HEIGHT/2);
        AffineTransform orig = g2.getTransform();
        // Center the scaled image under the mouse pointer.
        double x = loc.x - scale*WIDTH/2;
        double y = loc.y - scale*HEIGHT/2;
        g2.translate(x, y);
        g2.scale(scale, scale);
        g2.drawImage(mImagen, 0, 0, null);
        g2.setColor(Color.blue);
        Ellipse2D ellipse = new Ellipse2D.Double(100.0d, 100.0d, 100.0d, 100.0d);
        g2.fill(ellipse);
        g2.setTransform(orig);
    public void mousePressed(MouseEvent e) {
        if (SwingUtilities.isLeftMouseButton(e)){
            scale = scale + scaleInc;
        } else if (SwingUtilities.isRightMouseButton(e)){
            scale = scale - scaleInc;
            if(scale < MIN_SCALE)
                scale = MIN_SCALE;
        loc = e.getPoint();
        repaint();
    public void mouseClicked(MouseEvent e){}
    public void mouseReleased(MouseEvent e){}
    public void mouseEntered(MouseEvent e){}
    public void mouseExited(MouseEvent e){}
    public void mouseDragged(MouseEvent e){}
    public void mouseMoved(MouseEvent e){}
    public static void main(String[] args) {
        ZoomTest2 internalPanel = new ZoomTest2();
        internalPanel.setBorder(BorderFactory.createTitledBorder("Zoom test"));
        JFrame window = new JFrame();
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setLayout(new FlowLayout(FlowLayout.CENTER));
        window.add(internalPanel);
        window.pack();
        window.setVisible(true);
}