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ImageAnimator.javaAPI DocExample3643Mon Sep 22 13:30:30 BST 1997None

ImageAnimator

public class ImageAnimator extends Applet implements Runnable
This applet displays an image animation. It uses the MediaTracker class to load the images and verify that there are no errors.

Fields Summary
protected int
num_frames
protected Image[]
frames
protected int
framenum
protected MediaTracker
tracker
protected Thread
animator_thread
Constructors Summary
Methods Summary
public voidinit()
Read the basename and num_frames parameters. Then read in the images, using the specified base name. For example, if basename is images/anim, read images/anim0, images/anim1, etc. These are relative to the current document URL.

 // The thread for animation

                                           
     
    String basename = this.getParameter("basename");
    try { num_frames = Integer.parseInt(this.getParameter("num_frames")); }
    catch (NumberFormatException e) { num_frames = 0; }

    // getImage() creates an Image object from a URL specification,
    // but it doesn't actually load the images; that is done  asynchronously.
    // Store all the images in a MediaTracker so we can block until
    // they have all loaded.  This method must return promptly, so we don't
    // wait for them to load here.
    tracker = new MediaTracker(this);
    frames = new Image[num_frames];
    for(int i = 0; i < num_frames; i++) {
      frames[i] = this.getImage(this.getDocumentBase(), basename+i);
      tracker.addImage(frames[i], i);  // Add image to tracker, assigning an ID
    }
public voidpaint(java.awt.Graphics g)
Draw the current frame of the animation

 g.drawImage(frames[framenum], 0, 0, this);
public voidrun()
This is the body of the thread--the method that does the animation.

    // First, wait until all images have loaded completely.
    for (int i = 0; i < num_frames; i++) {
      this.showStatus("Loading frame: " + i);
      // Block until the specified image is loaded.  The ID argument is the
      // one we passed to addImage().
      try { tracker.waitForID(i); } catch (InterruptedException e) {;}
      // Check for errors loading it.  Display an error message if necessary
      if (tracker.isErrorID(i)) {
        this.showStatus("Error loading frame " + i + "; quitting.");
        return;
      }
    }
    this.showStatus("Loading frames: done.");  // Done loading all frames

    // Now do the animation: increment the framenumber, redraw, pause
    while(true) {
      if (++framenum >= frames.length) framenum = 0;
      repaint();
      try { Thread.sleep(200); } catch (InterruptedException e) { ; }
    }
public voidstart()
Create the animation thread and start it running

    if (animator_thread == null) {
      animator_thread = new Thread(this);
      animator_thread.start();
    }
public voidstop()
Stop the animation thread

    if ((animator_thread != null) && animator_thread.isAlive())
      animator_thread.stop();
    animator_thread = null;
public voidupdate(java.awt.Graphics g)
Don't clear the screen before calling paint()

 paint(g);