anchor.diff:          rootNode.size = new Size(systemWidth, systemHeight);
           break;
         case SpriteBoxTransformMode.nativePoints:
  +        systemWidth = size.width;
  +        systemHeight = size.height;
           break;
         default:
           assert(false);
  
positive.code:     assert(rootNode != null);
      assert(rootNode._spriteBox == null);
  
      // Setup root node
      this.rootNode = rootNode;
  
      // Setup transform mode
      this.transformMode = mode;
    }
  
    void _removeSpriteBoxReference(Node node) {
  
negative.code:     if (value == _rootNode) return;
  
      // Ensure that the root node has a size
      assert(_transformMode == SpriteBoxTransformMode.nativePoints
        || value.size.width > 0);
      assert(_transformMode == SpriteBoxTransformMode.nativePoints
        || value.size.height > 0);
  
      // Remove sprite box references
      if (_rootNode != null) _removeSpriteBoxReference(_rootNode);
  