anchor.diff:  }
   
   const double _kThumbRadius = 6.0;
  -const double _kThumbRadiusDisabled = 3.0;
  +const double _kActiveThumbRadius = 9.0;
  +const double _kDisabledThumbRadius = 4.0;
   const double _kReactionRadius = 16.0;
   const double _kTrackWidth = 144.0;
   final Color _kInactiveTrackColor = Colors.grey[400];
   final Color _kActiveTrackColor = Colors.grey[500];
  +final Tween<double> _kReactionRadiusTween = new Tween<double>(begin: _kThumbRadius, end: _kReactionRadius);
  +final Tween<double> _kThumbRadiusTween = new Tween<double>(begin: _kThumbRadius, end: _kActiveThumbRadius);
  +final ColorTween _kTrackColorTween = new ColorTween(begin: _kInactiveTrackColor, end: _kActiveTrackColor);
   
   class _RenderSlider extends RenderConstrainedBox {
     _RenderSlider({
  
positive.code:       ..onUpdate = _handleDragUpdate
        ..onEnd = _handleDragEnd;
      _reactionController = new AnimationController(duration: kRadialReactionDuration);
      _reaction = new Tween<double>(
        begin: _kThumbRadius,
        end: _kReactionRadius
      ).animate(new CurvedAnimation(
        parent: _reactionController,
        curve: Curves.ease
      ))..addListener(markNeedsPaint);
    }
  
    double get value => _value;
  
negative.code:     double trackActive = trackLeft + trackLength * value;
  
      Paint primaryPaint = new Paint()..color = enabled ? _activeColor : _kInactiveTrackColor;
      Paint trackPaint = new Paint()..color = _kTrackColorTween.evaluate(_reaction);
  
      double thumbRadius = enabled ? _kThumbRadiusTween.evaluate(_reaction) : _kDisabledThumbRadius;
      Point activeLocation = new Point(trackActive, trackCenter);
  
      if (enabled) {
        canvas.drawRect(new Rect.fromLTRB(trackLeft, trackTop, trackRight, trackBottom), trackPaint);
        if (_value > 0.0)
          canvas.drawRect(new Rect.fromLTRB(trackLeft, trackTop, trackActive, trackBottom), primaryPaint);
      } else {
        canvas.drawRect(new Rect.fromLTRB(trackLeft, trackTop, activeLocation.x - _kDisabledThumbRadius - 2, trackBottom), trackPaint);
        canvas.drawRect(new Rect.fromLTRB(activeLocation.x + _kDisabledThumbRadius + 2, trackTop, trackRight, trackBottom), trackPaint);
      }
  
      if (_reaction.status != AnimationStatus.dismissed) {
        Paint reactionPaint = new Paint()..color = _activeColor.withAlpha(kRadialReactionAlpha);
        canvas.drawCircle(activeLocation, _kReactionRadiusTween.evaluate(_reaction), reactionPaint);
      }
      canvas.drawCircle(activeLocation, thumbRadius, primaryPaint);
    }
  