anchor.diff:    final BoxPainter _painter;
   
     BoxDecoration get decoration => _painter.decoration;
  -  void set decoration (BoxDecoration value) {
  -    assert(value != null);
  -    if (value == _painter.decoration)
  +  void set decoration (BoxDecoration newDecoration) {
  +    assert(newDecoration != null);
  +    if (newDecoration == _painter.decoration)
         return;
       _removeBackgroundImageListenerIfNeeded();
  -    _painter.decoration = value;
  +    _painter.decoration = newDecoration;
       _addBackgroundImageListenerIfNeeded();
       markNeedsPaint();
     }
  
positive.code: 
    double _stepWidth;
    double get stepWidth => _stepWidth;
    void set stepWidth(double value) {
      if (value == _stepWidth)
        return;
      _stepWidth = value;
      markNeedsLayout();
    }
  
    double _stepHeight;
    double get stepHeight => _stepHeight;
    void set stepHeight(double value) {
      if (value == _stepHeight)
        return;
      _stepHeight = value;
      markNeedsLayout();
    }
  
  
negative.code: 
    Matrix4 _transform;
  
    void set transform(Matrix4 newTransform) {
      assert(newTransform != null);
      if (_transform == newTransform)
        return;
      _transform = new Matrix4.copy(newTransform);
      markNeedsPaint();
    }
  
  