Re: Zoom relative to mouse position


I've finally figured this out. Here's my code if you are interested:

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseWheelEvent;
import java.awt.event.MouseWheelListener;
import java.awt.geom.AffineTransform;
import java.awt.geom.NoninvertibleTransformException;
import java.awt.geom.Point2D;
import java.awt.geom.Rectangle2D;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

@SuppressWarnings("serial")
public class ZoomDemo extends JPanel implements Runnable {

AffineTransform tx = new AffineTransform();

Rectangle2D.Double rect1 = new Rectangle2D.Double(100, 100, 30, 60);
Rectangle2D.Double rect2 = new Rectangle2D.Double(150, 250, 60, 40);

public ZoomDemo() {
this.addMouseWheelListener(new ZoomHandler());
}

@Override
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2 = (Graphics2D) g;
g2.setColor(Color.RED);
g2.draw(tx.createTransformedShape(rect1));
g2.setColor(Color.BLUE);
g2.draw(tx.createTransformedShape(rect2));
}

private class ZoomHandler implements MouseWheelListener {

double scale = 1.0;

public void mouseWheelMoved(MouseWheelEvent e) {
if (e.getScrollType() == MouseWheelEvent.WHEEL_UNIT_SCROLL) {

Point2D p1 = e.getPoint();
Point2D p2 = null;
try {
p2 = tx.inverseTransform(p1, null);
} catch (NoninvertibleTransformException ex) {
// should not get here
ex.printStackTrace();
return;
}

scale -= (0.1 * e.getWheelRotation());
scale = Math.max(0.1, scale);

tx.setToIdentity();
tx.translate(p1.getX(), p1.getY());
tx.scale(scale, scale);
tx.translate(-p2.getX(), -p2.getY());

ZoomDemo.this.revalidate();
ZoomDemo.this.repaint();
}
}
}

public void run() {
JFrame f = new JFrame("Zoom Demo");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.getContentPane().add(this);
f.setSize(600, 600);
f.setLocationRelativeTo(null);
f.setVisible(true);
}

public static void main(String[] args) {
SwingUtilities.invokeLater(new ZoomDemo());
}
}












Amir Kouchekinia wrote:
Hi,

I am trying to figure out how to zoom relative to the mouse pointer
position. Below, please find my sample code.

When I initially position the mouse pointer on one corner of the red
rectangle and use the mouse wheel, I am able to zoom in and out as
expected. As soon as I move the pointer position, let's say to another
corner of the red rectangle, and try to zoom in or out, my position
relative to the rectangle shifts around.

I think I may be missing a transform or two. In another attempt, in the
mouseWheelMoved method, I inverted tx from the previous iteration and
transformed the mouse position p with the inverted transform before
recalculating the new transform; but the behavior got more erratic.


Any help is greatly appreciated. What am I missing here?

Thanks.

Here is my code:

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.event.MouseWheelEvent;
import java.awt.event.MouseWheelListener;
import java.awt.geom.AffineTransform;
import java.awt.geom.Path2D;
import java.awt.geom.Rectangle2D;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

@SuppressWarnings("serial")
public class ZoomDemo extends JPanel {

AffineTransform tx = new AffineTransform();

Rectangle2D.Double rect = new Rectangle2D.Double(100, 100, 20, 30);

public ZoomDemo() {
this.addMouseWheelListener(new ZoomHandler());
}

@Override
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2 = (Graphics2D) g;

Path2D.Double path;
g2.setColor(Color.RED);
path = new Path2D.Double(rect, tx);
g2.draw(path);
}

private class ZoomHandler implements MouseWheelListener {

Point oldPoint = null;

double scale = 1.0;

public void mouseWheelMoved(MouseWheelEvent e) {
if (e.getScrollType() == MouseWheelEvent.WHEEL_UNIT_SCROLL) {

scale += (.1 * e.getWheelRotation());
scale = Math.max(0.1, scale);
Point p = e.getPoint();

tx = AffineTransform.getTranslateInstance(p.getX(), p.getY());
tx.scale(scale, scale);
tx.translate(-p.getX(), -p.getY());

ZoomDemo.this.revalidate();
ZoomDemo.this.repaint();
}
}
}

public static void main(String[] args) {

JFrame f = new JFrame("ZoomDemo");
ZoomDemo zoomDemo = new ZoomDemo();
JScrollPane sp = new JScrollPane(zoomDemo);
f.getContentPane().add(sp);
f.setSize(500, 500);
f.setLocationRelativeTo(null);
f.setVisible(true);
}
}
.

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