package {
    import flash.display.*;
    import flash.events.*;
    import flash.utils.*;
    
    // A very simple animation class that demonstrates how to separate
    // animation duties from an object being animated
    public class @ax-actionscript-lib-animation-Animator extends EventDispatcher {
      // Stores a reference to the object being animated
      private var target:DisplayObject;
      // Each time an animation starts we record its start time in startTime
      private var startTime:Number;
      // The duration of an animation, in milliseconds
      private var duration:Number;
      // Each time an animation starts we record the target's start 
      // position in startX and startY
      private var startX:Number;    
      private var startY:Number;
      // Each time an animation starts we record the difference between the 
      // starting position and the end position in deltaX and deltaY
      private var deltaX:Number;
      private var deltaY:Number;
  
      // The constructor function accepts a reference to the object that 
      // will be animated
      public function @ax-actionscript-lib-animation-Animator (target:DisplayObject) {
        this.target = target;
      }    
  
      // Starts an animation that moves the target object from its current 
      // position to the specified new position (toX, toY), over 
      // 'duration' milliseconds
      public function animateTo (toX:Number, toY:Number, 
                                 duration:Number):void {
        // Remember where the target was when this animation started
        startX = target.x;
        startY = target.y;
  
        // Calculate the difference between the target's starting position
        // and final destination
        deltaX = toX - target.x;
        deltaY = toY - target.y;
        startTime = getTimer();
        
        // Remember how long this animation should take
        this.duration  = duration;
        
        // Begin listening for Event.ENTER_FRAME events. Each time a
        // scheduled screen-update occurs, we'll update the position of 
        // the target object
        target.addEventListener(Event.ENTER_FRAME, enterFrameListener);
      }
  
      // Handles Event.ENTER_FRAME events. 
      private function enterFrameListener (e:Event):void {
        // Calculate the time elapsed since the animation started
        var elapsed:Number = getTimer()-startTime;
        // Calculate how much time has passed in the animation, as a
        // percentage of its total duration
        var percentDone:Number = elapsed/duration;
        // If the animation is not yet complete...
        if (percentDone < 1) {
          // ...update the position of the target object
          updatePosition(percentDone);
        } else {
          // ...otherwise place the target object at its final destination,
          // and stop listening for Event.ENTER_FRAME events
          updatePosition(1);
          target.removeEventListener(Event.ENTER_FRAME, enterFrameListener);
        }
      }
  
      // Sets the position of the target object to a percentage of the
      // distance between the animation start point and end point
      private function updatePosition (percentDone:Number):void {
        target.x = startX + deltaX*percentDone;
        target.y = startY + deltaY*percentDone;
      }
    }
  }