anchor.diff:  
     void invalidateDraw(){
       validateNotDisposed();
  -    if(_lastDrawSize != null){
  +    if(_lastDrawSize != null) {
         _lastDrawSize = null;
         _invalidateParent();
       }
  
positive.code:     var tx = this.getTransform();
      CanvasUtil.transform(ctx, tx);
  
      ctx.drawImage(this._cacheCanvas, 0, 0);
      ctx.restore();
    }
  
negative.code:     requireArgument(isValidNumber(value), 'value');
      requireArgument(value >= 0 && value <= 1, 'value');
      _alpha = value;
      if(parent != null) {
        _invalidateParent();
      }
    }
  
    ThingParent get parent => _parent;
  