jdk.awt.MediaTracker

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*-aborted
*-complete
*-errored
*-loading
->media-tracker
add-image
check-all
check-id
error-any?
error-id?
get-errors-any
get-errors-id
remove-image
status-all
status-id
wait-for-all
wait-for-id

The MediaTracker class is a utility class to track the status of a number of media objects. Media objects could include audio clips as well as images, though currently only images are supported.

To use a media tracker, create an instance of MediaTracker and call its addImage method for each image to be tracked. In addition, each image can be assigned a unique identifier. This identifier controls the priority order in which the images are fetched. It can also be used to identify unique subsets of the images that can be waited on independently. Images with a lower ID are loaded in preference to those with a higher ID number.

Tracking an animated image might not always be useful due to the multi-part nature of animated image loading and painting, but it is supported. MediaTracker treats an animated image as completely loaded when the first frame is completely loaded. At that point, the MediaTracker signals any waiters that the image is completely loaded. If no ImageObservers are observing the image when the first frame has finished loading, the image might flush itself to conserve resources (see Image.flush()).

Here is an example of using MediaTracker:

import java.applet.Applet; import java.awt.Color; import java.awt.Image; import java.awt.Graphics; import java.awt.MediaTracker;

public class ImageBlaster extends Applet implements Runnable { MediaTracker tracker; Image bg; Image anim[] = new Image[5]; int index; Thread animator;

 // Get the images for the background (id == 0)
 // and the animation frames (id == 1)
 // and add them to the MediaTracker
 public void init() {
     tracker = new MediaTracker(this);
     bg = getImage(getDocumentBase(),
             "images/background.gif");
     tracker.addImage(bg, 0);
     for (int i = 0; i < 5; i++) {
         anim[i] = getImage(getDocumentBase(),
                 "images/anim"+i+".gif");
         tracker.addImage(anim[i], 1);
     }
 }

 // Start the animation thread.
 public void start() {
     animator = new Thread(this);
     animator.start();
 }

 // Stop the animation thread.
 public void stop() {
     animator = null;
 }

 // Run the animation thread.
 // First wait for the background image to fully load
 // and paint.  Then wait for all of the animation
 // frames to finish loading. Finally, loop and
 // increment the animation frame index.
 public void run() {
     try {
         tracker.waitForID(0);
         tracker.waitForID(1);
     } catch (InterruptedException e) {
         return;
     }
     Thread me = Thread.currentThread();
     while (animator == me) {
         try {
             Thread.sleep(100);
         } catch (InterruptedException e) {
             break;
         }
         synchronized (this) {
             index++;
             if (index >= anim.length) {
                 index = 0;
             }
         }
         repaint();
     }
 }

 // The background image fills the frame so we
 // don't need to clear the applet on repaints.
 // Just call the paint method.
 public void update(Graphics g) {
     paint(g);
 }

 // Paint a large red rectangle if there are any errors
 // loading the images.  Otherwise always paint the
 // background so that it appears incrementally as it
 // is loading.  Finally, only paint the current animation
 // frame if all of the frames (id == 1) are done loading,
 // so that we don't get partial animations.
 public void paint(Graphics g) {
     if ((tracker.statusAll(false) & MediaTracker.ERRORED) != 0) {
         g.setColor(Color.red);
         g.fillRect(0, 0, size().width, size().height);
         return;
     }
     g.drawImage(bg, 0, 0, this);
     if (tracker.statusID(1, false) == MediaTracker.COMPLETE) {
         g.drawImage(anim[index], 10, 10, this);
     }
 }

}

The MediaTracker class is a utility class to track
the status of a number of media objects. Media objects could
include audio clips as well as images, though currently only
images are supported.

To use a media tracker, create an instance of
MediaTracker and call its addImage
method for each image to be tracked. In addition, each image can
be assigned a unique identifier. This identifier controls the
priority order in which the images are fetched. It can also be used
to identify unique subsets of the images that can be waited on
independently. Images with a lower ID are loaded in preference to
those with a higher ID number.



Tracking an animated image
might not always be useful
due to the multi-part nature of animated image
loading and painting,
but it is supported.
MediaTracker treats an animated image
as completely loaded
when the first frame is completely loaded.
At that point, the MediaTracker
signals any waiters
that the image is completely loaded.
If no ImageObservers are observing the image
when the first frame has finished loading,
the image might flush itself
to conserve resources
(see Image.flush()).


Here is an example of using MediaTracker:



import java.applet.Applet;
import java.awt.Color;
import java.awt.Image;
import java.awt.Graphics;
import java.awt.MediaTracker;

public class ImageBlaster extends Applet implements Runnable {
     MediaTracker tracker;
     Image bg;
     Image anim[] = new Image[5];
     int index;
     Thread animator;

     // Get the images for the background (id == 0)
     // and the animation frames (id == 1)
     // and add them to the MediaTracker
     public void init() {
         tracker = new MediaTracker(this);
         bg = getImage(getDocumentBase(),
                 "images/background.gif");
         tracker.addImage(bg, 0);
         for (int i = 0; i < 5; i++) {
             anim[i] = getImage(getDocumentBase(),
                     "images/anim"+i+".gif");
             tracker.addImage(anim[i], 1);
         }
     }

     // Start the animation thread.
     public void start() {
         animator = new Thread(this);
         animator.start();
     }

     // Stop the animation thread.
     public void stop() {
         animator = null;
     }

     // Run the animation thread.
     // First wait for the background image to fully load
     // and paint.  Then wait for all of the animation
     // frames to finish loading. Finally, loop and
     // increment the animation frame index.
     public void run() {
         try {
             tracker.waitForID(0);
             tracker.waitForID(1);
         } catch (InterruptedException e) {
             return;
         }
         Thread me = Thread.currentThread();
         while (animator == me) {
             try {
                 Thread.sleep(100);
             } catch (InterruptedException e) {
                 break;
             }
             synchronized (this) {
                 index++;
                 if (index >= anim.length) {
                     index = 0;
                 }
             }
             repaint();
         }
     }

     // The background image fills the frame so we
     // don't need to clear the applet on repaints.
     // Just call the paint method.
     public void update(Graphics g) {
         paint(g);
     }

     // Paint a large red rectangle if there are any errors
     // loading the images.  Otherwise always paint the
     // background so that it appears incrementally as it
     // is loading.  Finally, only paint the current animation
     // frame if all of the frames (id == 1) are done loading,
     // so that we don't get partial animations.
     public void paint(Graphics g) {
         if ((tracker.statusAll(false) & MediaTracker.ERRORED) != 0) {
             g.setColor(Color.red);
             g.fillRect(0, 0, size().width, size().height);
             return;
         }
         g.drawImage(bg, 0, 0, this);
         if (tracker.statusID(1, false) == MediaTracker.COMPLETE) {
             g.drawImage(anim[index], 10, 10, this);
         }
     }
}

jdk.awt.MediaTracker

*-abortedclj

*-completeclj

*-erroredclj

*-loadingclj

->media-trackerclj

add-imageclj

check-allclj

check-idclj

error-any?clj

error-id?clj

get-errors-anyclj

get-errors-idclj

remove-imageclj

status-allclj

status-idclj

wait-for-allclj

wait-for-idclj

*-aborted^clj

*-complete^clj

*-errored^clj

*-loading^clj

->media-tracker^clj

add-image^clj

check-all^clj

check-id^clj

error-any?^clj

error-id?^clj

get-errors-any^clj

get-errors-id^clj

remove-image^clj

status-all^clj

status-id^clj

wait-for-all^clj

wait-for-id^clj