anchor.diff:      if (_cachedPaint == null) {
         _cachedPaint =  new Paint()
           ..color = new Color.fromARGB(_alpha, 0, 0, 0)
  -        ..setTransferMode(sky.TransferMode.srcOver);
  +        ..setTransferMode(sky.TransferMode.srcOver)
  +        ..isAntiAlias = false;
       }
       return _cachedPaint;
     }
  
positive.code: class RenderClipOval extends RenderProxyBox {
    RenderClipOval({ RenderBox child }) : super(child);
  
    void paint(PaintingCanvas canvas, Offset offset) {
      if (child != null) {
        Rect rect = offset & size;
        canvas.saveLayer(rect, new Paint());
        Path path = new Path();
        path.addOval(rect);
        canvas.clipPath(path);
        canvas.paintChild(child, offset.toPoint());
        canvas.restore();
      }
  
negative.code:   Paint get _paint {
      if (_cachedPaint == null) {
        _cachedPaint = new Paint()
          ..setColorFilter(new sky.ColorFilter.mode(_color, _transferMode))
          ..isAntiAlias = false;
      }
      return _cachedPaint;
    }
  