CS 596 Java Programming Fall Semester, 1998 Scaling an Image
	To Applet Index San Diego State University -- This page last updated 03-Jan-99

The scrollbar value ranges from from 10 to 200. These values represent the percentage used to scale the image. A value of 200 displays an image twice the size of the orginal image.

<DIV ALIGN="center">
   <APPLET 
      ARCHIVE="AppletClasses.jar" 
      CODE="ImageScaleApplet.class" 
      WIDTH=350 HEIGHT=330>
      Your browser does not support Java applets, so
      you can not see this applet operate.
   </APPLET>
</DIV>

import java.awt.*;
import java.awt.image.ImageObserver;

public class ImageCanvas extends Canvas
  {
  Image displayImage;
  int imageWidth;
  int imageHeight;
  int displayWidth;
  int displayHeight;
    
  public ImageCanvas( Image toDisplay )
    {
    displayImage = toDisplay;
    imageWidth = displayImage.getWidth( this );
    imageHeight = displayImage.getHeight( this );
    displayWidth = imageWidth;
    displayHeight = imageHeight;
    }
  
  public void paint( Graphics display) 
    {
    //center image
    int startX = (imageWidth - displayWidth) / 2;
    int startY = (imageHeight - displayHeight) / 2;

    //drawImage scales image to fit displayWidth, height 
    display.drawImage( displayImage, startX, startX, 
                  displayWidth, displayHeight,
                  this );
    }

  // Override the default action, which would clear the display region
  // before drawing the image again. The default causes some flicker.
  // Here we just redraw the image. It covers the entire area.
  public void update(Graphics display)
    {
    paint( display);
    }
  
  // Scale display image
  public void scaleImage( int percentScale)
    {
    displayWidth = (imageWidth * percentScale) / 100;
    displayHeight =   (imageHeight * percentScale) / 100;
    repaint();
    }
  }

import java.awt.*;
import java.applet.Applet;
import java.awt.Image;
import java.awt.image.ImageObserver;
import java.awt.event.AdjustmentListener;
import java.awt.event.AdjustmentEvent;

public class ImageScaleApplet extends Applet
  {
  private Scrollbar imageChanger = 
      new Scrollbar( Scrollbar.HORIZONTAL, 
                  100, //Initial value
                  1,   //Not used, area visiable
                  10,   // min value, seems to be block change rate
                  201 ); //max value, 1 compensates for visisble area
                      // subtracted from max value.
  
  private ImageCanvas tigerCanvas;
    
  public void init() 
    {
    Image tiger = getImage( "../images/tiger.gif" );
    tigerCanvas = new ImageCanvas( tiger);
    
    imageChanger.addAdjustmentListener( new ImageAdjustment() );
    setLayout( new BorderLayout() );
    add( BorderLayout.NORTH, imageChanger );
    add( BorderLayout.CENTER, tigerCanvas ); 
    }  
  
  private Image getImage( String imageName)
    {
    Image loadedImage = null;
    try 
      {      
      loadedImage = super.getImage( getCodeBase(), imageName );
      
      //Insure image is downloaded before showing it
      MediaTracker tracker = new MediaTracker( this );
      tracker.addImage( loadedImage, 0 );
      tracker.waitForID( 0 );
      }
    catch (InterruptedException netProblem ) 
      {
      System.out.println( "error");
      }
    return loadedImage;
    }
  
  class ImageAdjustment implements AdjustmentListener 
    {
    public void adjustmentValueChanged( AdjustmentEvent event )
      {
      // Use the value of the scrollbar as the scale rate of image
      tigerCanvas.scaleImage( event.getValue());
      }
    }              
  }

Visitors since 03-Jan-99