The Juggler controls the progress of your application by propagating the time passed between two render frames.

The RenderLoop and Stage class provides Juggler instances which are driven by the browsers animation frames. You can also create your own Juggler instance and control the time by yourself. Because Juggler implements the Animatable interface it can be added to other Juggler instances too.

See also: Tween, Transition, DelayedCall

Examples:

var tween = new Tween(sprite, 1.0, TransitionFunction.easeIn);
tween.animate.x.to(1.0);
stage.juggler.add(tween);

// create a "gameJuggler" who controls all my animations.
var gameJuggler = new Juggler();
// start all animations controlled by "gameJuggler".
stage.juggler.add(gameJuggler);
// stop all animations controlled by "gameJuggler".
stage.juggler.remove(gameJuggler);

class Juggler implements Animatable {

 _AnimatableLink _firstAnimatableLink;
 _AnimatableLink _lastAnimatableLink;

 num _elapsedTime = 0.0;

 Juggler() {
   _firstAnimatableLink = new _AnimatableLink();
   _lastAnimatableLink = _firstAnimatableLink;
 }

 //-----------------------------------------------------------------------------------------------
 //-----------------------------------------------------------------------------------------------

 num get elapsedTime => _elapsedTime;

 //-----------------------------------------------------------------------------------------------

 void add(Animatable animatable) {

   if (animatable is! Animatable) {
     throw new ArgumentError("The supplied animatable does not extend type Animatable.");
   }

   if (this.contains(animatable) == false) {
     var animatableLink = new _AnimatableLink();
     _lastAnimatableLink.animatable = animatable;
     _lastAnimatableLink.nextAnimatableLink = animatableLink;
     _lastAnimatableLink = animatableLink;
   }
 }

 //-----------------------------------------------------------------------------------------------

 void remove(Animatable animatable) {

   if (animatable != null) {
     var link = _firstAnimatableLink;
     while(identical(link, _lastAnimatableLink) == false) {
       if (identical(link.animatable, animatable)) {
         link.animatable = null;
         break;
       }
       link = link.nextAnimatableLink;
     }
   }
 }

 //-----------------------------------------------------------------------------------------------

 bool contains(Animatable animatable) {

   if (animatable != null) {
     var link = _firstAnimatableLink;
     while(identical(link, _lastAnimatableLink) == false) {
       if (identical(link.animatable, animatable)) return true;
       link = link.nextAnimatableLink;
     }
   }

   return false;
 }

 //-----------------------------------------------------------------------------------------------

 void removeTweens(DisplayObject displayObject) {

   var link = _firstAnimatableLink;
   while(identical(link, _lastAnimatableLink) == false) {
     var animatable = link.animatable;
     if (animatable is Tween && identical(animatable.displayObject, displayObject)) {
       link.animatable = null;
     }
     link = link.nextAnimatableLink;
   }
 }

 //-----------------------------------------------------------------------------------------------

 bool containsTweens(DisplayObject displayObject) {

   var link = _firstAnimatableLink;
   while(identical(link, _lastAnimatableLink) == false) {
     var animatable = link.animatable;
     if (animatable is Tween && identical(animatable.displayObject, displayObject)) {
       return true;
     }
     link = link.nextAnimatableLink;
   }

   return false;
 }

 //-----------------------------------------------------------------------------------------------

 void purge() {

   var link = _firstAnimatableLink;
   while(identical(link, _lastAnimatableLink) == false) {
     link.animatable = null;
   }

   _lastAnimatableLink = _firstAnimatableLink;
 }

 //-----------------------------------------------------------------------------------------------
 //-----------------------------------------------------------------------------------------------

 Tween tween(DisplayObject displayObject, num time, [EaseFunction transitionFunction]) {

   Tween tween = transitionFunction != null
       ? new Tween(displayObject, time, transitionFunction)
       : new Tween(displayObject, time);

   add(tween);
   return tween;
 }

 //-----------------------------------------------------------------------------------------------

 Transition transition(num startValue, num targetValue, num time, EaseFunction transitionFunction, void onUpdate(num value)) {

   Transition transition = new Transition(startValue, targetValue, time, transitionFunction);
   transition.onUpdate = onUpdate;
   add(transition);

   return transition;
 }

 //-----------------------------------------------------------------------------------------------

 DelayedCall delayCall(Function action, num delay) {

   DelayedCall delayedCall = new DelayedCall(action, delay);
   add(delayedCall);

   return delayedCall;
 }

 //-----------------------------------------------------------------------------------------------

 AnimationGroup addGroup(List<Animatable> animatables) {
   var animationGroup = new AnimationGroup();
   for(int i = 0; i < animatables.length; i++) {
     animationGroup.add(animatables[i]);
   }
   add(animationGroup);
   return animationGroup;
 }

 //-----------------------------------------------------------------------------------------------

 AnimationChain addChain(List<Animatable> animatables) {
   var animationChain = new AnimationChain();
   for(int i = 0; i < animatables.length; i++) {
     animationChain.add(animatables[i]);
   }
   add(animationChain);
   return animationChain;
 }

 //-----------------------------------------------------------------------------------------------
 //-----------------------------------------------------------------------------------------------

 bool advanceTime(num time) {

   _elapsedTime += time;

   // Call advanceTime of current animatables.
   // Do not call advanceTime of newly added animatables.

   var link = _firstAnimatableLink;
   var lastLink = _lastAnimatableLink;

   while(identical(link, lastLink) == false) {

     var animatable = link.animatable;
     if (animatable == null) {

       var nextLink = link.nextAnimatableLink;
       link.animatable = nextLink.animatable;
       link.nextAnimatableLink = nextLink.nextAnimatableLink;

       if (identical(nextLink, lastLink)) lastLink = link;
       if (identical(nextLink, _lastAnimatableLink)) _lastAnimatableLink = link;

     } else if (animatable.advanceTime(time) == false) {
       link.animatable = null;
     } else {
       link = link.nextAnimatableLink;
     }
   }

   return true;
 }

}