Need help: BufferedImage and zooming

Question

please help me understand what i am doing wrong. i am having a hard time understanding the concept behind BufferedImage and zooming. the applet code loads an image as its background. after loading, you can draw line segments on it. but when i try to zoom in, the image in the background remains the same in terms of size, line segments are the only ones that are being zoomed, and the mouse coordinates are confusing.
import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.awt.geom.*;
import javax.swing.*;
import javax.imageio.*;
import java.io.*;
import java.util.ArrayList;
import java.io.IOException;
import java.net.URL;
import java.awt.image.*;
public class Testing extends JApplet {
     private String url;
     private Map map;
     public void init() {
     public void start()
          url = "http://localhost/image.gif";
              map = new Map(url);
             getContentPane().add(map, "Center");
             validate();
             map.validate();
class Map extends JPanel implements MouseListener, MouseMotionListener{
     private Image image;
     private ArrayList<Point2D> points;
     private ArrayList<Line2D> lineSegment;
     private Point2D startingPoint;
     private int mouseX;
     private int mouseY;
     private BufferedImage bimg;
     private AffineTransform xform;
     private AffineTransform inverse;
     private double zoomFactor = 1;
     public Map(String url)
                     super();
          //this.image = image;
          try
               image = ImageIO.read(new URL(url));
          catch(Exception e)
          Insets insets = getInsets();
          xform = AffineTransform.getTranslateInstance(insets.left, insets.top);
          xform.scale(zoomFactor,zoomFactor);
          try {
               inverse = xform.createInverse();
          } catch (NoninvertibleTransformException e) {
               System.out.println(e);
          points = new ArrayList();
          startingPoint = new Point();
          bimg = new BufferedImage(this.image.getWidth(this), this.image.getHeight(this), BufferedImage.TYPE_INT_ARGB);
          repaintBImg();
          addMouseListener(this);
          addMouseMotionListener(this);
     public void paintComponent(Graphics g)
        Graphics2D g2d = (Graphics2D)g;
          g2d.addRenderingHints(new RenderingHints(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON));
          g2d.addRenderingHints(new RenderingHints(RenderingHints.KEY_RENDERING , RenderingHints.VALUE_RENDER_QUALITY ));
        bimg = (BufferedImage)image;
        g2d.drawRenderedImage(bimg, xform);
        if(!points.isEmpty())
             for(int i=0; i<points.size(); i++)
                  if(i > 0)
                       drawLineSegment(g2d,points.get(i-1),points.get(i));
                  drawPoint(g2d, points.get(i));
        if(startingPoint != null)
            drawTempLine(startingPoint, g2d);
        else
            mouseX = 0;
            mouseY = 0;
     private void repaintBImg()
          bimg.flush();
          Graphics2D g2d = bimg.createGraphics();
          g2d.addRenderingHints(new RenderingHints(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON));
          g2d.addRenderingHints(new RenderingHints(RenderingHints.KEY_RENDERING , RenderingHints.VALUE_RENDER_QUALITY ));
        g2d.drawRenderedImage(bimg, xform);
        g2d.dispose();
     private void drawPoint(Graphics2D g2d, Point2D p)
        int x = (int)(p.getX() * zoomFactor);
        int y = (int)(p.getY() * zoomFactor);
        int w = (int)(13 * zoomFactor);
        int h = (int)(13 * zoomFactor);
          g2d.setColor(Color.ORANGE);
          g2d.setStroke(new BasicStroke(1.0F));
        g2d.fillOval(x - w / 2, y - h / 2, w, h);
        g2d.setColor(Color.BLACK);
        g2d.drawOval(x - w / 2, y - h / 2, w - 1, h - 1);
     private void drawLineSegment(Graphics2D g2d, Point2D p1, Point2D p2)
          double x1 = p1.getX() * zoomFactor;
             double y1 = p1.getY() * zoomFactor;
             double x2 = p2.getX() * zoomFactor;
             double y2 = p2.getY() * zoomFactor;
             g2d.setColor(Color.RED);
             g2d.setStroke(new BasicStroke(3.0F));
             g2d.draw(new java.awt.geom.Line2D.Double(x1, y1, x2, y2));
         private void drawTempLine(Point2D p, Graphics2D g2d)
             int startX = (int)(p.getX() * zoomFactor);
             int startY = (int)(p.getY() * zoomFactor);
             if(mouseX != 0 && mouseY != 0)
                     g2d.setColor(Color.RED);
                      g2d.setStroke(new BasicStroke(2.0F));
                      g2d.drawLine(startX, startY, mouseX, mouseY);
     public void mouseClicked(MouseEvent e)
     public void mouseDragged(MouseEvent e)
          mouseX = (int)(e.getX()*zoomFactor);
          mouseY = (int)(e.getY()*zoomFactor);
          repaint();
     public void mousePressed(MouseEvent e)
          if(e.getButton() == 1)
               points.add(inverse.transform(e.getPoint(), null));
               if(points.size() > 0)
                    startingPoint = points.get(points.size()-1);
                    mouseX = mouseY = 0;
               repaint();
          else if(e.getButton() == 2)
               zoomFactor = zoomFactor + .05;
               repaintBImg();
          else if(e.getButton() == 3)
               zoomFactor = zoomFactor - .05;
               repaintBImg();
     public void mouseReleased(MouseEvent e)
          if(e.getButton() == 1)
               points.add(inverse.transform(e.getPoint(), null));
          repaint();
     public void mouseEntered(MouseEvent mouseevent)
     public void mouseExited(MouseEvent mouseevent)
     public void mouseMoved(MouseEvent mouseevent)
}Message was edited by:
hardc0d3r

Answer 1

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.awt.geom.*;
import java.io.*;
import java.net.URL;
import java.util.*;
import javax.imageio.*;
import javax.swing.*;
public class ZoomTesting extends JApplet {
    public void init() {
        //String dir = "file:/" + System.getProperty("user.dir");
        //System.out.printf("dir = %s%n", dir);
        String url = "http://localhost/image.gif";
                     //dir + "/images/cougar.jpg";
        MapPanel map = new MapPanel(url);
        getContentPane().add(map, "Center");
    public static void main(String[] args) {
        JApplet applet = new ZoomTesting();
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(applet);
        f.setSize(400,400);
        f.setLocation(200,200);
        applet.init();
        f.setVisible(true);
class MapPanel extends JPanel implements MouseListener, MouseMotionListener {
    private BufferedImage image;
    private ArrayList<Point2D> points;
    private Point2D startingPoint;
    private int mouseX;
    private int mouseY;
    private AffineTransform xform;
    private AffineTransform inverse;
    RenderingHints hints;
    private double zoomFactor = 1;
    public MapPanel(String url) {
        super();
        try {
            image = ImageIO.read(new URL(url));
        } catch(Exception e) {
            System.out.println(e.getClass().getName() +
                               " = " + e.getMessage());
        Map<RenderingHints.Key, Object> map =
                    new HashMap<RenderingHints.Key, Object>();
        map.put(RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);
        map.put(RenderingHints.KEY_RENDERING,
                RenderingHints.VALUE_RENDER_QUALITY);
        hints = new RenderingHints(map);
        setTransforms();
        points = new ArrayList<Point2D>();
        startingPoint = new Point();
        addMouseListener(this);
        addMouseMotionListener(this);
    private void setTransforms() {
        Insets insets = getInsets();
        xform = AffineTransform.getTranslateInstance(insets.left, insets.top);
        xform.scale(zoomFactor,zoomFactor);
        try {
            inverse = xform.createInverse();
        } catch (NoninvertibleTransformException e) {
            System.out.println(e);
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D)g;
        g2d.setRenderingHints(hints);
        g2d.drawRenderedImage(image, xform);
        if(!points.isEmpty()) {
            for(int i=0; i<points.size(); i++) {
                if(i > 0)
                    drawLineSegment(g2d,points.get(i-1),points.get(i));
                drawPoint(g2d, points.get(i));
        if(startingPoint != null) {
            drawTempLine(startingPoint, g2d);
        } else {
            mouseX = 0;
            mouseY = 0;
    private void drawPoint(Graphics2D g2d, Point2D p) {
        int x = (int)(p.getX() * zoomFactor);
        int y = (int)(p.getY() * zoomFactor);
        int w = (int)(13 * zoomFactor);
        int h = (int)(13 * zoomFactor);
        g2d.setColor(Color.ORANGE);
        g2d.setStroke(new BasicStroke(1.0F));
        g2d.fillOval(x - w / 2, y - h / 2, w, h);
        g2d.setColor(Color.BLACK);
        g2d.drawOval(x - w / 2, y - h / 2, w - 1, h - 1);
    private void drawLineSegment(Graphics2D g2d, Point2D p1, Point2D p2) {
        double x1 = p1.getX() * zoomFactor;
        double y1 = p1.getY() * zoomFactor;
        double x2 = p2.getX() * zoomFactor;
        double y2 = p2.getY() * zoomFactor;
        g2d.setColor(Color.RED);
        g2d.setStroke(new BasicStroke(3.0F));
        g2d.draw(new java.awt.geom.Line2D.Double(x1, y1, x2, y2));
    private void drawTempLine(Point2D p, Graphics2D g2d) {
        int startX = (int)(p.getX() * zoomFactor);
        int startY = (int)(p.getY() * zoomFactor);
        if(mouseX != 0 && mouseY != 0) {
            g2d.setColor(Color.RED);
            g2d.setStroke(new BasicStroke(2.0F));
            g2d.drawLine(startX, startY, mouseX, mouseY);
    public void mouseClicked(MouseEvent e) {}
    public void mouseDragged(MouseEvent e) {
        mouseX = (int)(e.getX()*zoomFactor);
        mouseY = (int)(e.getY()*zoomFactor);
        repaint();
    public void mousePressed(MouseEvent e) {
        if(e.getButton() == 1) {
            points.add(inverse.transform(e.getPoint(), null));
            if(points.size() > 0) {
                startingPoint = points.get(points.size()-1);
                mouseX = mouseY = 0;
        } else if(e.getButton() == 2) {
            zoomFactor = zoomFactor + .05;
            setTransforms();
        } else if(e.getButton() == 3) {
            zoomFactor = zoomFactor - .05;
            setTransforms();
        repaint();
    public void mouseReleased(MouseEvent e) {
        if(e.getButton() == 1) {
            points.add(inverse.transform(e.getPoint(), null));
        repaint();
    public void mouseEntered(MouseEvent mouseevent) {}
    public void mouseExited(MouseEvent mouseevent) {}
    public void mouseMoved(MouseEvent mouseevent) {}
}