anchor.diff:  
   
   
  -
  
positive.code:   }
  
    void update() {
      if(object == null) return;
      var center = object.target;
      var position = object.position;
      var offset = position - center;
  
negative.code:       _state = STATE_ZOOM;
        _zoomStart.setValues(e.client.x.toDouble(), e.client.y.toDouble());
      }
      if (_mouseMoveSubscription != null) _mouseMoveSubscription.cancel();
      if (_mouseUpSubscription != null) _mouseUpSubscription.cancel();
      _mouseMoveSubscription = html.document.onMouseMove.listen(_onMouseMove);
      _mouseUpSubscription = html.document.onMouseUp.listen(_onMouseUp);
    }
  