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Apache License 2.0

About

This is a dart port of the original java Universal Tween Engine created by Aurelien Ribbon. This readme is an adaptation of the original's engine readme and includes how things are handled in the dart version of the engine.

You can find a demo of the library here. The engine might have some bugs. Use at your own risk.

Introduction

The Universal Tween Engine enables the interpolation of every attribute from any object in any dart project (server or client side). Tweens are 'fire and forget'.

Implementing

Dart, unlike javascript, has no string accessors for objects, such as myObject['myProperty']. Reflection methods are still under development in Dart, and they will be slow. So, there are two ways of telling the engine which properties you want to tween. The first one is very useful if you do not have control over the class you want to tween a property of. The second one is a bit less verbose but requires code in the class you want to tween.

Using TweenAccessor

Create an accessor that implements the TweenAccessor interface, register it to the engine, and animate anything you want!

class MyAccessor implements TweenAccessor<MyClass>{
  static const Type1 = 1;
  
  int getValues(MyClass target, Tween tween, int tweenType, List<num> returnValues){
    if ( tweenType == MyAccessor.Type1 ){
      returnValues[0] = target.x;
      returnValues[1] = target.y;
      return 2;
    }
    return 0;
  }

  void setValues(MyClass target, Tween tween, int tweenType, List<num> newValues){
    if ( tweenType == MyAccessor.Type1 ){
      target.x = newValues[0];
      target.y = newValues[1];
    }
  }
}

class MyClass{
  num x=0, y=0;
}

main(){
   Tween.registerAccessor(MyClass, new MyAccessor());
}

Using Tweenable

Make sure the class you want to tween implements the Tweenable interface.

class MyTweenable implements Tweenable {
  static const int ANSWER = 1;
  static const int CIRCLE = 2;

  int answer = 42;
  num circle = 6.2831853;

  /**
   * Updates [returnValues] with the values of the properties you want to tween
   * when you run a `tweenType` tween.
   * Returns the number of values set in [returnValues].
   */
  int getTweenableValues(int tweenType, Tween tween, List<num> returnValues) {
    if (tweenType == ANSWER) {
      returnValues[0] = answer;
    } else if (tweenType == CIRCLE) {
      returnValues[0] = circle;
    }
    return 1;
  }

  /**
   * Updates this object's properties with values from [newValues],
   * in the [tweenType] fashion of `getTweenableValues`.
   */
  void setTweenableValues(int tweenType, Tween tween, List<num> newValues) {
    if (tweenType == ANSWER) {
      answer = newValues[0];
    } else if (tweenType == CIRCLE) {
      circle = newValues[0];
    }
  }
}

Updating

For the tween to be completed, a continuous call to your TweenManager's .update(delta) is needed. The delta parameter represents the time elapsed in milliseconds since last call to update.

An easy way to obtain the delta is the window.animationFrame method:


TweenManager myManager;
main(){
  ...
  myManager = new TweenManager();
  window.animationFrame.then(update);
}

num lastUpdate = 0;
update(num delta){
  num deltaTime = (delta - lastUpdate) / 1000;
  lastUpdate = delta;
  
  myManager.update(deltaTime);
  window.animationFrame.then(update);
}

Next, send your objects to another position (here x=20 and y=30), with a smooth elastic transition, during 1 second.

// Arguments are 
// 1. the target
// 2. the type of interpolation
// 3. the duration in seconds
// Additional methods specify the target values, and the easing function. 

main(){
  ...
  Tween.to(myClass, MyAccessor.Type1, 1.0)
    ..targetValues = [20, 30]
    ..easing = Elastic.INOUT;
  window.animationFrame.then(update);
}

API

Possibilities are:

Tween.to(...);   // interpolates from the current values to the targets
Tween.from(...); // interpolates from the given values to the current ones
Tween.set(...);  // apply the target values without animation (useful with a delay)
Tween.call(...); // calls a method (useful with a delay)

Current options are:

myTween.delay = 0.5;
myTween.repeat(2, 0.5);
myTween.repeatYoyo(2, 0.5); 
myTween.pause();
myTween.resume();
myTween.callback = callback;
myTween.callbackTriggers = flags;
myTween.userData = obj;

You can of course chain everything (with dart's method cascading):

new Tween.to(...)
 ..delay = 1
 ..repeat(2, 0.5)
 ..start(myManager);

By altering the delta parameter, adding slow-motion, fast-motion or reverse play is easy, you just need to change the speed of the update:

myManager.update(delta * speed);

Create some powerful animation sequences!

new Timeline.sequence()
    // First, set all objects to their initial positions
    ..push(Tween.set(...))
    ..push(Tween.set(...))
    ..push(Tween.set(...))

    // Wait 1s
    ..pushPause(1.0)

    // Move the objects around, one after the other
    ..push(Tween.to(...))
    ..push(Tween.to(...))
    ..push(Tween.to(...))

    // Then, move the objects around at the same time
    ..beginParallel()
        ..push(Tween.to(...))
        ..push(Tween.to(...))
        ..push(Tween.to(...))
    ..end()

    // And repeat the whole sequence 2 times
    // with a 0.5s pause between each iteration
    ..repeatYoyo(2, 0.5)

    // Let's go!
    ..start(myManager);

You can also quickly create timers:

new Tween.call(myCallback)
  ..delay = 3000
  ..start(myManager);

Main features

Testing suite

Since 0.10.0, tweenengine has a (crude) test suite. It leverages the unittest package.

To run it, you'll either need Dartium or dart2js.

Using Dartium

Browse test/test.html.

Using dart2js

Compile test/test.dart to test/test.dart.js :

$ dart2js test/test.dart -v -o test/test.dart.js

Then, browse test/test.html.