Mouse Coordinate issues caused by Scaling Components in a JScrollPane

Question

Hi All,
I've been attempting to write a program that includes a simple modeler. However, I've been having some trouble with being able to select components when attempting to implement zoom functionality - when I "zoom" (which is done via scroll wheel) using the scale Graphics2D method, while it zooms correctly, the mouse location of components do not seem scale.
I've tried one of the solutions found on the forums here (create a custom event queue that adjusts the mouse coordinates) and while it seemed to work initially, if I zoom in and adjust the current view position using the scrollbars, certain components contained in the JPane will become un-selectable and I haven't been able to work out why.
I've attached a SSCCE that reproduces the problem below - it implements a JScrollPane with a JPane with a few selectable shapes set as the Viewport. The zoom is done using the mouse scroll wheel (with wheel up being zoom in and wheel down being zoom out)
Any help in order to fix the selection/de-selection issues on zoom would be greatly appreciated! I've spent some time reading through the forums here but have unfortunately not been able to find a workable solution around it.
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
public class Tester extends JScrollPane
    public Tester() {
        this.setViewportView(new Model());
    public static void main (String[] args) {
        JFrame main = new JFrame();
        main.add(new Tester());
        main.setSize(500,300);
        main.setResizable(false);
        main.setVisible(true);
class Model extends JPanel implements MouseListener, MouseWheelListener
    private GfxClass selection = null;
    private static double zoomLevel = 1;
    // zoom methods
    public void setZoom(double zoom) {
        if( zoom < 0 && zoomLevel > 1.0)
            zoomLevel += zoom;
        if( zoom > 0 && zoomLevel < 5.0)
            zoomLevel += zoom;
    public static double getZoom() { return zoomLevel; }
    public void resetZoom() { zoomLevel = 1; }
    public Model() {
        super(null);
        addMouseListener(this);
        addMouseWheelListener(this);
        MyEventQueue meq = new MyEventQueue();
        Toolkit.getDefaultToolkit().getSystemEventQueue().push(meq);
        for(int i = 0; i <7; i++) {
            double angle = Math.toRadians(i * 360 / 7);
            GfxClass oc_tmp = new GfxClass((int)(200 + 150 * Math.cos(angle)), (int)(125 + 100 * Math.sin(angle)), "Element"+i);
            add(oc_tmp);
        repaint();
    public void paint (Graphics g) {
        Graphics2D g2 = (Graphics2D) g.create();
        AffineTransform oldTr=g2.getTransform();
        g2.scale(getZoom(),getZoom());
        super.paint(g2);
        g2.setTransform(oldTr);
        setBackground (Color.white);
        super.paintBorder(g2);
    private static class MyEventQueue extends EventQueue  {
        protected void dispatchEvent(AWTEvent event) {
            AWTEvent event2=event;
            if ( !(event instanceof MouseWheelEvent) && (event instanceof MouseEvent) ) {
                if ( event.getSource() instanceof Component && event instanceof MouseEvent) {
                    MouseEvent me=(MouseEvent)event2;
                    Component c=(Component)event.getSource();
                    Component cursorComponent=SwingUtilities.getDeepestComponentAt(c, me.getX(), me.getY());
                    JPanel zContainer= getZoomedPanel(cursorComponent);
                    if (zContainer!=null) {
                        int x=me.getX();
                        Point p=SwingUtilities.convertPoint(zContainer,0,0,(Component)event.getSource());
                        int cX=me.getX()-p.x;
                        x=x-cX+(int)(cX/getZoom());
                        int y=me.getY();
                        int cY=me.getY()-p.y;
                        y=y-cY+(int)(cY/getZoom());
                        MouseEvent ze = new MouseEvent(me.getComponent(), me.getID(), me.getWhen(), me.getModifiers(), x, y, me.getClickCount(), me.isPopupTrigger());
                        event2=ze;
            super.dispatchEvent(event2);
    public static JPanel getZoomedPanel(Component c) {
        if (c == null)
            return null;
        else if (c instanceof Model)
            return (Model)c;
        else
            return getZoomedPanel(c.getParent());
    private void deselectAll() {
        if(selection != null)
            selection.setSelected(false);
        selection = null;
    public void mouseClicked(MouseEvent arg0)  {    }
    public void mouseEntered(MouseEvent arg0)  {    }
    public void mouseExited(MouseEvent arg0)   {    }
    public void mouseReleased(MouseEvent arg0) {    }   
    public void mousePressed(MouseEvent me) {
        Component c1 = findComponentAt(me.getX(),me.getY());
        if(c1 instanceof GfxClass)
            if(selection != null)
                selection.setSelected(false);
            selection = (GfxClass)c1;
            selection.setSelected(true);
        else
            deselectAll();
        repaint();
        return;
    public void mouseWheelMoved(MouseWheelEvent e) { // controls zoom
            int notches = e.getWheelRotation();
            if (notches < 0)
                setZoom(0.1);
            else
                setZoom(-0.1);
            this.setSize(new Dimension((int)(500*getZoom()),(int)(300*getZoom())));           
            this.setPreferredSize(new Dimension((int)(500*getZoom()),(int)(300*getZoom())));     
            repaint();
class GfxClass extends Component { // simple graphical component
    private boolean isSelected = false;
    private String name;
    public GfxClass(int xPos, int yPos, String name) {
        this.name = name;
        this.setLocation(xPos,yPos);
        this.setSize(100,35);
    public void setSelected(boolean b) {
        if( b == isSelected )
            return;
        isSelected = b;
        repaint();
    public boolean isSelected() {
        return isSelected;
    public void paint(Graphics g2) {
        Graphics2D g = (Graphics2D)g2;
        if( isSelected )
            g.setColor(Color.RED);
        else
            g.setColor(Color.BLUE);
        g.fill(new Ellipse2D.Double(0,0,100,35));
        g.setColor(Color.BLACK);
        g.drawString(name, getSize().width/2 - 25, getSize().height/2);
}Edited by: Kys99 on Feb 22, 2010 9:09 AM
Edited by: Kys99 on Feb 22, 2010 9:10 AM

Answer 1

Delete your EventQueue class. Change one line of code in your mouse pressed method.
public void mousePressed(MouseEvent me) {
    Component c1 = findComponentAt((int) (me.getX()/getZoom()),
                                   (int) (me.getY()/getZoom()));
}