/*
 * @(#)Animator.java	1.5 99/07/12
 *
 * Copyright (c) 1997 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Sun grants you ("Licensee") a non-exclusive, royalty free, license to use,
 * modify and redistribute this software in source and binary code form,
 * provided that i) this copyright notice and license appear on all copies of
 * the software; and ii) Licensee does not utilize the software in a manner
 * which is disparaging to Sun.
 *
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING ANY
 * IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR
 * NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN AND ITS LICENSORS SHALL NOT BE
 * LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING
 * OR DISTRIBUTING THE SOFTWARE OR ITS DERIVATIVES. IN NO EVENT WILL SUN OR ITS
 * LICENSORS BE LIABLE FOR ANY LOST REVENUE, PROFIT OR DATA, OR FOR DIRECT,
 * INDIRECT, SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER
 * CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY, ARISING OUT OF THE USE OF
 * OR INABILITY TO USE SOFTWARE, EVEN IF SUN HAS BEEN ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGES.
 *
 * This software is not designed or intended for use in on-line control of
 * aircraft, air traffic, aircraft navigation or aircraft communications; or in
 * the design, construction, operation or maintenance of any nuclear
 * facility. Licensee represents and warrants that it will not use or
 * redistribute the Software for such purposes.
 */

import java.awt.*;
import java.awt.event.*;
import java.applet.Applet;
import java.applet.AudioClip;
import java.util.Vector;
import java.util.Hashtable;
import java.util.Enumeration;
import java.net.URL;
import java.net.MalformedURLException;
import java.util.List;
import java.util.ArrayList;
import java.util.Iterator;

/**
 * An applet that plays a sequence of images, as a loop or a one-shot.
 * Can have a soundtrack and/or sound effects tied to individual frames.
 * See the <a href="http://java.sun.com/applets/applets/Animator/">Animator
 * home page</a> for details and updates.
 *
 * @author Herb Jellinek
 * @version 1.5, 07/12/99
 */
public class Animator extends Applet implements Runnable, MouseListener {
    int appWidth = 0;                // Animator width
    int appHeight = 0;               // Animator height
    Thread engine = null;            // Thread animating the images
    boolean userPause = false;       // True if thread currently paused by user
    boolean loaded = false;          // Can we paint yet?
    boolean error = false;           // Was there an initialization error?
    Animation animation = null;      // Animation this animator contains
    String hrefTarget = null;        // Frame target of reference URL if any
    URL hrefURL = null;              // URL link for information if any
 
    static final String sourceLocation = 
                          "http://java.sun.com/applets/applets/Animator/";
    static final String userInstructions = "shift-click for errors, info";
    static final int STARTUP_ID    = 0;
    static final int BACKGROUND_ID = 1;
    static final int ANIMATION_ID  = 2;

    /**
     * Applet info.
     */
    public String getAppletInfo() {
	return "Animator v1.10 (02/05/97), by Herb Jellinek";
    }

    /**
     * Parameter info.
     */
    public String[][] getParameterInfo() {
	String[][] info = {
	    {"imagesource", 	"URL", 	       "a directory"},
	    {"startup", 	"URL", 	       "image displayed at start-up"},
	    {"backgroundcolor", "int", "background color (24-bit RGB number)"},
	    {"background", 	"URL", 	      "image displayed as background"},
	    {"startimage", 	"int", 	       "index of first image"},
	    {"endimage", 	"int", 	       "index of last image"},
	    {"namepattern",     "URL",         "generates indexed names"},
	    {"images",          "URLs",        "list of image indices"},
	    {"href",		"URL",	       "page to visit on mouse-click"},
	    {"target",		"name",	       "frame to put that page in"},
	    {"pause", 	        "int", 	       "global pause, milliseconds"},
	    {"pauses", 	        "ints",     "individual pauses, milliseconds"},
	    {"repeat", 	        "boolean",     "repeat? true or false"},
	    {"positions",       "coordinates", "path images will follow"},
	    {"soundsource",	"URL", 	       "audio directory"},
	    {"soundtrack",	"URL", 	       "background music"},
	    {"sounds",		"URLs",	       "list of audio samples"},
	};
	return info;
    }

    /**
     * Show a crude "About" box.  Displays credits, errors (if any), and
     * parameter values and documentation.
     */
    void showDescription() {
	DescriptionFrame description = new DescriptionFrame();	    
	description.tell("\t\t"+getAppletInfo()+"\n");
	description.tell("Updates, documentation at "+sourceLocation+"\n\n");
	description.tell("Document base: "+getDocumentBase()+"\n");
	description.tell("Code base: "+getCodeBase()+"\n\n");
	
	Object errors[] = animation.tracker.getErrorsAny();
	if (errors != null) {
	    description.tell("Applet image errors:\n");
	    for (int i = 0; i < errors.length; i++) {
		if (errors[i] instanceof Image) {
		    AnimationFrame frame = (AnimationFrame) 
                                              animation.frames.get(i);
                    URL url = frame.imageLocation;
		    if (url != null) {
			description.tell(" "+url+" not loaded\n");
		    }
		}
	    }
	    description.tell("\n");
	}
	if (animation.frames == null || animation.frames.size() == 0)
	    description.tell("\n** No images loaded **\n\n");
	description.tell("Applet parameters:\n");
	description.tell(" width = "+getParameter("WIDTH")+"\n");
	description.tell(" height = "+getParameter("HEIGHT")+"\n");
	String params[][] = getParameterInfo();
	for (int i = 0; i < params.length; i++) {
	    String name = params[i][0];
	    description.tell(" "+name+" = "+getParameter(name)+
			     "\t ["+params[i][2]+"]\n");
	}
	description.show();
    }

    /**
     * Local version of getParameter for debugging purposes.
     */
    public String getParam(String key) {
	String result = getParameter(key);
	return result;
    }

    /**
     * Get parameters and parse them
     */
    public void handleParams() {
        try {
	    String param = getParam("IMAGESOURCE");
	    animation.imageSource = (param == null) ? getDocumentBase() :
                new URL(getDocumentBase(), param + "/");
	
	    String href = getParam("HREF");
	    if (href != null) {
		try {
		    hrefURL = new URL(getDocumentBase(), href);
		} catch (MalformedURLException e) {
		    showParseError(e);
		}
	    }

	    hrefTarget = getParam("TARGET");
	    if (hrefTarget == null)
		hrefTarget = "_top";
	    param = getParam("PAUSE");
            if (param != null)
                animation.setGlobalPause(Integer.parseInt(param));
	    param = getParam("REPEAT");
	    animation.repeat = (param == null) ? true :
                (param.equalsIgnoreCase("yes") ||
                 param.equalsIgnoreCase("true"));
	    int startImage = 1;
	    int endImage = 1;
	    param = getParam("ENDIMAGE");
	    if (param != null) {
		endImage = Integer.parseInt(param);
		param = getParam("STARTIMAGE");
		if (param != null) {
		    startImage = Integer.parseInt(param);
		}
                param = getParam("NAMEPATTERN");
                animation.prepareImageRange(startImage, endImage, param);
	    } else {
		param = getParam("STARTIMAGE");
		if (param != null) {
		    startImage = Integer.parseInt(param);
		    param = getParam("NAMEPATTERN");
		    animation.prepareImageRange(startImage, endImage, param);
		} else {
		    param = getParam("IMAGES");
		    if (param == null) {
			showStatus("No legal IMAGES, STARTIMAGE, or ENDIMAGE "+
				   "specified.");
			error = true;
			return;
		    } else {
			animation.parseImages(param, getParam("NAMEPATTERN"));
		    }
		}
	    }

	    param = getParam("BACKGROUND");
	    if (param != null)
		animation.backgroundImageURL = new URL(animation.imageSource,
                                                       param);
	    param = getParam("BACKGROUNDCOLOR");
	    if (param != null)
		animation.backgroundColor = decodeColor(param);
	    param = getParam("STARTUP");
	    if (param != null)
		animation.startUpImageURL = new URL(animation.imageSource, 
                                                    param);
	    param = getParam("SOUNDSOURCE");
	    animation.soundSource = (param == null) ? animation.imageSource :
                new URL(getDocumentBase(), param + "/");	
	    param = getParam("SOUNDS");
	    if (param != null)
		animation.parseSounds(param);
	    param = getParam("PAUSES");
	    if (param != null)
		animation.parseDurations(param);
	    param = getParam("POSITIONS");
	    if (param != null) 
		animation.parsePositions(param);
	    param = getParam("SOUNDTRACK");
	    if (param != null)
		animation.soundTrackURL = new URL(
                                          animation.soundSource, param);
	} catch (MalformedURLException e) {
	    showParseError(e);
	} catch (ParseException e) {
	    showParseError(e);
	}
    }

    private Color decodeColor(String s) {
	int val = 0;
	try {
	    if (s.startsWith("0x")) {
		val = Integer.parseInt(s.substring(2), 16);
	    } else if (s.startsWith("#")) {
		val = Integer.parseInt(s.substring(1), 16);
	    } else if (s.startsWith("0") && s.length() > 1) {
		val = Integer.parseInt(s.substring(1), 8);
	    } else {
		val = Integer.parseInt(s, 10);
	    }
	    return new Color(val);
	} catch (NumberFormatException e) {
	    return null;
	}
    }
    
    /**
     * Initialize the applet.  Get parameters.
     */
    public void init() {
        
        //animation.tracker = new MediaTracker(this);
	appWidth = getSize().width;
	appHeight = getSize().height;
        animation = new Animation(this);
        handleParams();
        animation.init();
	addMouseListener(this);
        Thread me = Thread.currentThread();
        me.setPriority(Thread.MIN_PRIORITY);
        userPause = false;
    }

    public void destroy() {
        removeMouseListener(this);
    }

    void tellLoadingMsg(String file, String fileType) {
	showStatus("Animator: loading "+fileType+" "+file);
    }

    void tellLoadingMsg(URL url, String fileType) {
	tellLoadingMsg(url.toExternalForm(), fileType);
    }

    void clearLoadingMessage() {
	showStatus("");
    }
    
    void loadError(String fileName, String fileType) {
	String errorMsg = "Animator: Couldn't load "+fileType+" "+
	    fileName;
	showStatus(errorMsg);
	System.err.println(errorMsg);
	error = true;
	repaint();
    }

    void loadError(URL badURL, String fileType) {
	loadError(badURL.toExternalForm(), fileType);
    }

    void showParseError(Exception e) {
	String errorMsg = "Animator: Parse error: "+e;
	showStatus(errorMsg);
	System.err.println(errorMsg);
	error = true;
	repaint();
    }

    /**
     * Run the animation. This method is called by class Thread.
     * @see java.lang.Thread
     */
    public void run() {
        Thread me = Thread.currentThread();
        if (animation.frames == null)
            return;
        if ((appWidth <= 0) || (appHeight <= 0))
            return;
	try {
            while (engine == me) {
                // Get current frame and paint it, play its sound
                AnimationFrame thisFrame = (AnimationFrame) 
                               animation.frames.get(animation.currentFrame);
                repaint();
                if (thisFrame.sound != null)
                    thisFrame.sound.play();

                animation.currentFrame++;
                 // Check if we are done
                if (animation.currentFrame >= animation.frames.size()) {
                    if (animation.repeat)
                        animation.currentFrame = 0;
                    else return;
                }

                // Pause for duration or longer if user paused
                try {        
                    Thread.sleep(thisFrame.duration);
                    synchronized(this) {
                        while (userPause) {
                            animation.stopPlaying();
                            wait();
                        }
                    }
                }
                catch (InterruptedException e) {
                }
            }
        } finally {
            synchronized(this) {
            if (engine == me)
                animation.stopPlaying();
            }
        }
    }

    /**
     * No need to clear anything; just paint.
     */
    public void update(Graphics g) {
	paint(g);
    }

    /**
     * Paint the current frame
     */
    public void paint(Graphics g) {
        if (error || ! loaded) {
            if (animation.startUpImage != null) {
		if (animation.tracker.checkID(STARTUP_ID)) {
		    if (animation.backgroundColor != null) {
			g.setColor(animation.backgroundColor);
			g.fillRect(0, 0, appWidth, appHeight);
		    }
		    g.drawImage(animation.startUpImage, 0, 0, this);
		}
	    } else {
		if ((animation.backgroundImage != null) &&
		     (animation.tracker.checkID(BACKGROUND_ID)))
			g.drawImage(animation.backgroundImage, 0, 0, this);
		else 
		    g.clearRect(0, 0, appWidth, appHeight);
	    }
        } else {
            animation.paint(g);
        }
    }

    /**
     * Start the applet by forking an animation thread.
     */
    public void start() {
	engine = new Thread(this);
	engine.start();
	showStatus(getAppletInfo());
    }

    /**
     * Stop the insanity, um, applet.
     */
    public synchronized void stop() {
	engine = null;
        animation.stopPlaying();
         if (userPause) {
            userPause = false;
            notify();
        }
    }

    /**
     * Pause the thread when the user clicks the mouse in the applet.
     * If the thread has stopped (as in a non-repeat performance),
     * restart it.
     */
    public synchronized void mousePressed(MouseEvent event) {
        event.consume();
	if ((event.getModifiers() & InputEvent.SHIFT_MASK) != 0) {
	    showDescription();
	    return;
	} else if (hrefURL != null) {
            //Let mouseClicked handle this.
            return;
        } else if (loaded) {
	    userPause = !userPause;
            if (!userPause) {
                animation.startPlaying();
                notifyAll();
            }
	}
    }

    public void mouseClicked(MouseEvent event) {
	if ((hrefURL != null) &&
	        ((event.getModifiers() & InputEvent.SHIFT_MASK) == 0)) {
	    getAppletContext().showDocument(hrefURL, hrefTarget);
	}
    }

    public void mouseReleased(MouseEvent event) {
    }

    public void mouseEntered(MouseEvent event) {
	showStatus(getAppletInfo()+" -- "+userInstructions);
    }

    public void mouseExited(MouseEvent event) {
        showStatus("");
    }    
}

/**
 * A class that represents an animation to be displayed by the applet
 */
class Animation extends Object {
    static final int STARTUP_ID    = 0;
    static final int BACKGROUND_ID = 1;
    static final int ANIMATION_ID  = 2;
    static final String imageLabel = "image";
    static final String soundLabel = "sound";

    int globalPause = 1300;        // global pause in milleseconds
    List frames = null;            // List holding frames of animation
    int currentFrame;              // Index into images for current position
    Image startUpImage = null;     // The startup image if any
    Image backgroundImage = null;  // The background image if any
    AudioClip soundTrack = null;   // The soundtrack for this animation
    Color backgroundColor = null;  // Background color if any
    URL backgroundImageURL = null; // URL of background image if any
    URL startUpImageURL = null;    // URL of startup image if any 
    URL soundTrackURL = null;      // URL of soundtrack
    URL imageSource = null;        // Directory or URL for images
    URL soundSource = null;        // Directory or URL for sounds
    boolean repeat;                // Repeat the animation if true
    Image offScrImage;             // Offscreen image
    Graphics offScrGC;             // Offscreen graphics context
    MediaTracker tracker;          // MediaTracker used to load images
    Animator owner;                // Applet that contains this animation

    Animation(Animator container) {
        super();
        owner = container;
    }

    void init() {
        tracker = new MediaTracker(owner);
	currentFrame = 0;
        loadAnimationMedia();
	startPlaying();
    }

    void setGlobalPause(int pause) {
        globalPause = pause;
    }

    /**
     * Loads the images and sounds involved with this animation
     */
    void loadAnimationMedia() {
        URL badURL;
        boolean error;
        try {
            if (startUpImageURL != null) {
                owner.tellLoadingMsg(startUpImageURL, imageLabel);
                startUpImage = fetchImageAndWait(startUpImageURL, STARTUP_ID);
                if (tracker.isErrorID(STARTUP_ID)) {
                    owner.loadError(startUpImageURL, "start-up image");
                }
                owner.repaint();
            }
	    
	    if (backgroundImageURL != null) {
	         owner.tellLoadingMsg(backgroundImageURL, imageLabel);
	        backgroundImage = fetchImageAndWait(backgroundImageURL, 
                                                    BACKGROUND_ID);
	        if (tracker.isErrorID(BACKGROUND_ID))
                    owner.loadError(backgroundImageURL, 
                                        "background image");
		owner.repaint();
            }

	    // Fetch the animation frame images
            Iterator iterator = frames.iterator();
            while(iterator.hasNext()) {
                AnimationFrame frame = (AnimationFrame) iterator.next();
                owner.tellLoadingMsg(frame.imageLocation, imageLabel);
                frame.image = owner.getImage(frame.imageLocation);
                tracker.addImage(frame.image, ANIMATION_ID);
                try {
                    tracker.waitForID(ANIMATION_ID);
                } catch (InterruptedException e) {}
	    }

	    if (soundTrackURL != null && soundTrack == null) {
		owner.tellLoadingMsg(soundTrackURL, imageLabel);
		soundTrack = owner.getAudioClip(soundTrackURL);
		if (soundTrack == null) {
		    owner.loadError(soundTrackURL, "soundtrack");
		    return;
		}
	    }

            // Load the sounds into their frames
            iterator = frames.iterator();
            while(iterator.hasNext()) {
                AnimationFrame frame = (AnimationFrame) iterator.next();
                if (frame.soundLocation != null) {
                    owner.tellLoadingMsg(frame.soundLocation, soundLabel);
                    try {
                        frame.sound = owner.getAudioClip(frame.soundLocation);
                    } catch (Exception ex) {
                        owner.loadError(frame.soundLocation, soundLabel);
                    }
                }
	    }

	    owner.clearLoadingMessage();
	    offScrImage = owner.createImage(owner.appWidth, owner.appHeight);
	    offScrGC = offScrImage.getGraphics();
	    offScrGC.setColor(Color.lightGray);
            owner.loaded = true;
	    error = false;
	} catch (Exception e) {
	    error = true;
	    e.printStackTrace();
	}
    }

    /**
     * Fetch an image and wait for it to come in.  Used to enforce a load
     * order for background and startup images.
     */
    Image fetchImageAndWait(URL imageURL, int trackerClass) 
                              throws InterruptedException {
	Image image = owner.getImage(imageURL);
	tracker.addImage(image, trackerClass);
	tracker.waitForID(trackerClass);
	return image;
    }

    /**
     * Stuff a range of image names into a List
     * @return a List of image URLs.
     */
    void prepareImageRange(int startImage, int endImage, String pattern)
    throws MalformedURLException {
	frames = new ArrayList(Math.abs(endImage - startImage) + 1);
	if (pattern == null)
	    pattern = "T%N.gif";
	if (startImage > endImage) {
	    for (int i = startImage; i >= endImage; i--) {
                AnimationFrame frame = new AnimationFrame();
		frames.add(frame);
                frame.duration = globalPause;
                frame.imageLocation = new URL(imageSource, 
                                              doSubst(pattern, i+""));
	    }
	} else {
	    for (int i = startImage; i <= endImage; i++) {
                AnimationFrame frame = new AnimationFrame();
		frames.add(frame);
                frame.duration = globalPause;
                frame.imageLocation = new URL(imageSource,
                                              doSubst(pattern, i+""));
	    }
	}
    }

    /**
     * Parse the SOUNDS parameter.  It looks like
     * train.au||hello.au||stop.au, etc., where each item refers to a
     * source image.  Empty items mean that the corresponding image
     * has no associated sound.
     */
    void parseSounds(String attr) throws MalformedURLException {
	int frameIndex = 0;
	int numFrames = frames.size();
	for (int i = 0; (i < attr.length()) && (frameIndex < numFrames); ) {
	    int next = attr.indexOf('|', i);
	    if (next == -1) next = attr.length();
	    String sound = attr.substring(i, next);
	    if (sound.length() != 0) {
                AnimationFrame frame = (AnimationFrame) frames.get(frameIndex);
		frame.soundLocation = new URL(soundSource, sound);
	    }
	    i = next + 1;
	    frameIndex++;
        }
    }

    /**
     * Parse the IMAGES parameter.  It looks like
     * 1|2|3|4|5, etc., where each number (item) names a source image.
     */
    void parseImages(String attr, String pattern) 
                           throws MalformedURLException {
        frames = new ArrayList();
	if (pattern == null)
	    pattern = "T%N.gif";
	for (int i = 0; i < attr.length(); ) {
	    int next = attr.indexOf('|', i);
	    if (next == -1) next = attr.length();
	    String file = attr.substring(i, next);
            AnimationFrame frame = new AnimationFrame();
            frames.add(frame);
            frame.imageLocation = new URL(imageSource, doSubst(pattern, file));
            frame.duration = globalPause;
	    i = next + 1;
	}
    }

    /**
     * Parse the PAUSES parameter.  It looks like
     * 1000|500|||750, etc., where each item corresponds to a
     * source image.  Empty items mean that the corresponding image
     * has no special duration, and should use the global one.
     *
     * @return a Hashtable of Integer pauses keyed to Integer
     * frame numbers.
     */
    void parseDurations(String attr) {
	int imageNum = 0;
	int numImages = frames.size();
	for (int i = 0; (i < attr.length()) && (imageNum < numImages); ) {
	    int next = attr.indexOf('|', i);
	    if (next == -1) next = attr.length();
            AnimationFrame aFrame = (AnimationFrame) frames.get(imageNum);
	    if (i != next) {
		int duration = Integer.parseInt(attr.substring(i, next));
                aFrame.duration = duration;
	    }
	    i = next + 1;
	    imageNum++;
	}
    }

    /**
     * Parse a String of form xxx@yyy and return a Point.
     */
    Point parsePoint(String s) throws ParseException {
	int atPos = s.indexOf('@');
	if (atPos == -1) throw new ParseException("Illegal position: "+s);
	return new Point(Integer.parseInt(s.substring(0, atPos)),
			 Integer.parseInt(s.substring(atPos + 1)));
    }

    /**
     * Parse the POSITIONS parameter.  It looks like
     * 10@30|11@31|||12@20, etc., where each item is an X@Y coordinate
     * corresponding to a source image.  Empty items mean that the
     * corresponding image has the same position as the preceding one.
     *
     * @return a Hashtable of Points keyed to Integer frame numbers.
     */
    void parsePositions(String param)
    throws ParseException {
	int imageNum = 0;
	int numImages = frames.size();
	for (int i = 0; (i < param.length()) && (imageNum < numImages); ) {
	    int next = param.indexOf('|', i);
	    if (next == -1) 
                next = param.length();
	    if (i != next) {
                AnimationFrame frame = (AnimationFrame) frames.get(imageNum);
                frame.position = parsePoint(param.substring(i, next));
            }
	    i = next + 1;
	    imageNum++;
	}
    }

    /**
     * Substitute an integer some number of times in a string, subject to
     * parameter strings embedded in the string.
     * Parameter strings:
     *   %N - substitute the integer as is, with no padding.
     *   %<digit>, for example %5 - substitute the integer left-padded with
     *        zeros to <digits> digits wide.
     *   %% - substitute a '%' here.
     * @param inStr the String to substitute within
     * @param theInt the int to substitute, as a String.
     */
    String doSubst(String inStr, String theInt) {
	String padStr = "0000000000";
	int length = inStr.length();
	StringBuffer result = new StringBuffer(length);
	
	for (int i = 0; i < length;) {
	    char ch = inStr.charAt(i);
	    if (ch == '%') {
		i++;
		if (i == length) {
		    result.append(ch);
		} else {
		    ch = inStr.charAt(i);
		    if (ch == 'N' || ch == 'n') {
			// just stick in the number, unmolested
			result.append(theInt);
			i++;
		    } else {
			int pad;
			if ((pad = Character.digit(ch, 10)) != -1) {
			    // we've got a width value
			    String numStr = theInt;
			    String scr = padStr+numStr;
			    result.append(scr.substring(scr.length() - pad));
			    i++;
			} else {
			    result.append(ch);
			    i++;
			}
		    }
		}
	    } else {
		result.append(ch);
		i++;
	    }
	}
	return result.toString();
    }	

    void startPlaying() {
	if (soundTrack != null)
	    soundTrack.loop();
    }

    void stopPlaying() {
	if (soundTrack != null)
	    soundTrack.stop();
    }

    public void paint(Graphics g) {
        int xPos = 0;
        int yPos = 0;
        if ((frames.size() > 0) && tracker.checkID(ANIMATION_ID) && 
                                                          (offScrGC != null)) {
            AnimationFrame frame = (AnimationFrame) frames.get(currentFrame);
            Image image = frame.image;
            if (backgroundImage == null) {
                offScrGC.clearRect(0, 0, owner.appWidth, owner.appHeight);
            }
            else
                offScrGC.drawImage(backgroundImage, 0, 0, owner);
            Point pos = null;
            if (frame.position != null) {
                xPos = frame.position.x;
                yPos = frame.position.y;
            }
            if (backgroundColor != null) {
                offScrGC.setColor(backgroundColor);
                offScrGC.fillRect(0, 0, owner.appWidth, owner.appHeight);
                offScrGC.drawImage(image, xPos, yPos, backgroundColor, owner);
            } else {
                offScrGC.drawImage(image, xPos, yPos, owner);
            }
            if (offScrImage != null)
                g.drawImage(offScrImage, 0, 0, owner);
        }
    }
}

/**
 * Instances of this class represent a single frame of an animation
 * There can be an image, sound, and position associated with each frame
 */
class AnimationFrame extends Object {
    static final String imageLabel = "image";
    static final String soundLabel = "sound";

    URL imageLocation = null; // Directory or URL of this frames image
    URL soundLocation = null; // Directory or URL of this frames sound
    int duration;             // Duration time for this frame in milliseconds
    AudioClip sound;          // Sound associated with this frame object
    Image image;              // Image associated with this frame
    Point position;           // Position of this frame

}

/**
 * ParseException: signals a parameter parsing problem.
 */
class ParseException extends Exception {
    ParseException(String s) {
	super(s);
    }
}

/**
 * DescriptionFrame: implements a pop-up "About" box.
 */
class DescriptionFrame extends Frame implements ActionListener {
    static final int rows = 27;
    static final int cols = 70;
    TextArea info;
    Button cancel;

    DescriptionFrame() {
	super("Animator v1.10");
	add("Center", info = new TextArea(rows, cols));
	info.setEditable(false);
	info.setBackground(Color.white);
	Panel buttons = new Panel();
	add("South", buttons);
	buttons.add(cancel = new Button("Cancel"));
	cancel.addActionListener(this);
	pack();
    }

    public void show() {
	info.select(0,0);
	super.show();
    }

    void tell(String s) {
	info.append(s);
    }

    public void actionPerformed(ActionEvent e) {
	setVisible(false);
    }
}