anchor.diff:    GameBase(String appName, String canvasSelector, int width, int height,
         {this.spriteSheetName: 'assets',
         this.bodyDefsName: 'assets',
  -      bool webgl: false})
  +      bool webgl: false,
  +      bool depthTest: true,
  +      bool blending: true})
         : canvas = querySelector(canvasSelector),
           helper = new GameHelper(appName),
           webgl = webgl,
  
positive.code:   /// which contains the assets. Usually the game itself.
    GameBase.noAssets(
        String appName, String canvasSelector, int width, int height,
        {bool webgl: false})
        : this(appName, canvasSelector, width, height,
              spriteSheetName: null, bodyDefsName: null, webgl: webgl);
  
    GameBase.noCanvas(String appNahme)
        : canvas = null,
  
negative.code:   void start() {
      _init().then((_) {
        _lastTimeP = window.performance.now();
  
        var physicsSystem = world.systems.firstWhere((system) => system.group == 1, orElse: () => null);
        if (null != physicsSystem) {
          physicsLoop();
        }
        window.requestAnimationFrame(_firstUpdate);
      });
    }
  