anchor.diff:      });
     }
   
  +  void stop() {
  +    _stop = true;
  +  }
  +
     void physicsLoop() {
       var time = window.performance.now();
       world.delta = (time - _lastTimeP) / 1000;
       _lastTimeP = time;
       world.process(1);
   
  -    new Future.delayed(new Duration(milliseconds: 5), physicsLoop);
  +    if (!_stop) {
  +      new Future.delayed(new Duration(milliseconds: 5), physicsLoop);
  +    }
     }
   
     void _firstUpdate(double time) {
  
positive.code:     world.delta = delta;
      _lastTime = time;
      world.process();
      window.requestAnimationFrame((time) => update(time: time / 1000.0));
    }
  
    void _handleFullscreen(Event e) {
  
negative.code:   SpriteSheet spriteSheet;
    double _lastTime;
    double _lastTimeP;
    bool fullscreen = false;
    bool _stop = false;
  
    /// [appName] is used to refernce assets and has to be the name of the library
    /// which contains the assets. Usually the game itself.
  