Re: Draw a rectangle keeping aspect ratio of viewport

Here is an example contrived from some earlier code that Knute kindly
provided to centre the image in the scroll pane.

I believe Peter that the scroll pane is complicating things, which is
further complicated by the resize event??

Sorry this is longer than anticipated but works

import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.JViewport;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.swing.JScrollPane;

public class TestScale extends JPanel {

     static BufferedImage image;
     int imageW,imageH;
     private static JViewport vp;
     private static Point p;
     private static int zoom = 1;
     private static JScrollPane sp;
     private static Rectangle rect;
     /**
      * This method initializes
      *
      */

    public TestScale() throws IOException {
        super();
        initialize();
        image = ImageIO.read(new File("Sunset2.JPG"));
        imageW = image.getWidth();
        imageH = image.getHeight();
        rect = new Rectangle();
        setPreferredSize(new Dimension(imageW,imageH));
        }

     public void paintComponent(Graphics g) {
         int x = Math.max(getWidth() - imageW,0) / 2;
         int y = Math.max(getHeight() - imageH,0) / 2;
         g.drawImage(image,x,y,imageW,imageH,null);
         drawRect(g);
     }

     /**
      * This method initializes this
      *
      */
     private void initialize() {
         this.setSize(new Dimension(800, 600));
     
     }

     private static void drawRect(Graphics g) {
    int x1, y1, x2, y2;
    int startx = 0;
         int starty = 0;

         Graphics2D g2d = (Graphics2D) g;
         Rectangle vpBounds = sp.getViewport().getBounds();

         // is image width smaller or larger than viewport?
    if (getScaledImageDimension().width < vpBounds.width) {

             startx = (getScaledImageDimension().width / 2);
         } else { // nope

             startx = (int) vpBounds.x + (vpBounds.width / 2);

         }

    // is image height smaller or larger than viewport?
         if (getScaledImageDimension().height < vpBounds.height) {

             starty = getScaledImageDimension().height / 2;
         } else {

             starty = (int) vpBounds.y + (vpBounds.height / 2);

         }

         rect.setBounds(new Rectangle(startx, starty, 30 * zoom, 30 *
zoom));

         g2d.setColor(Color.WHITE);
      g2d.draw(rect);
         }

     //startx *= getZoomLevel();
     private static Dimension getScaledImageDimension() {
    return new Dimension(image.getWidth() * zoom, image.getHeight() * zoom );
     }

     public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
             public void run() {
                 try {
                     final TestScale t = new TestScale();
                     final JFrame f = new JFrame();
                     f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

                     sp = new JScrollPane(t);
                     f.add(sp,BorderLayout.CENTER);

                     JMenuBar mb = new JMenuBar();
                     f.setJMenuBar(mb);

                     JMenu m = new JMenu("Scale");
                     mb.add(m);

                     final JMenuItem oneX = new JMenuItem("1X");
                     final JMenuItem threeX = new JMenuItem("3X");

                     oneX.setEnabled(false);
                     oneX.addActionListener(new ActionListener() {
                         public void actionPerformed(ActionEvent ae) {
                             oneX.setEnabled(false);
                             threeX.setEnabled(true);
                             t.imageW /= 3;
                             t.imageH /= 3;
                             t.setPreferredSize(
                             new Dimension(t.imageW,t.imageH));
                             zoom = 1;
                             t.revalidate();
                             f.repaint();
                         }

                     });
                     m.add(oneX);

                     threeX.addActionListener(new ActionListener() {
                         public void actionPerformed(ActionEvent ae) {
                             threeX.setEnabled(false);
                             oneX.setEnabled(true);
                             t.imageW *= 3;
                             t.imageH *= 3;
                             t.setPreferredSize(
                              new Dimension(t.imageW,t.imageH));
                             zoom = 3;
                             t.revalidate();
                             f.repaint();

                             EventQueue.invokeLater(new Runnable() {
                                 public void run() {
                                     vp = sp.getViewport();
                                     p = new Point(
                                      (t.imageW - vp.getWidth())/2,
                                      (t.imageH - vp.getHeight())/2);
                                     vp.setViewPosition(p);
                                 }
                             });
                         }

                     });
                     m.add(threeX);

                     f.pack();
                     f.setVisible(true);
                 } catch (IOException ioe) {
                     ioe.printStackTrace();
                 }
             }
         });

     }
}

Rich