anchor.diff:        ..onUpdate = _handleDragUpdate
         ..onEnd = _handleDragEnd;
       _reactionController = new AnimationController(duration: kRadialReactionDuration);
  -    _reaction = new Tween<double>(
  -      begin: _kThumbRadius,
  -      end: _kReactionRadius
  -    ).animate(new CurvedAnimation(
  +    _reaction = new CurvedAnimation(
         parent: _reactionController,
         curve: Curves.ease
  -    ))..addListener(markNeedsPaint);
  +    )..addListener(markNeedsPaint);
     }
   
     double get value => _value;
  
positive.code:     double trackActive = trackLeft + trackLength * value;
  
      Paint primaryPaint = new Paint()..color = enabled ? _activeColor : _kInactiveTrackColor;
      Paint trackPaint = new Paint()..color = _active ? _kActiveTrackColor : _kInactiveTrackColor;
  
      double thumbRadius = enabled ? _kThumbRadius : _kThumbRadiusDisabled;
  
      canvas.drawRect(new Rect.fromLTRB(trackLeft, trackTop, trackRight, trackBottom), trackPaint);
      if (_value > 0.0)
        canvas.drawRect(new Rect.fromLTRB(trackLeft, trackTop, trackActive, trackBottom), primaryPaint);
  
      Point activeLocation = new Point(trackActive, trackCenter);
      if (_reaction.status != AnimationStatus.dismissed) {
        Paint reactionPaint = new Paint()..color = _activeColor.withAlpha(kRadialReactionAlpha);
        canvas.drawCircle(activeLocation, _reaction.value, reactionPaint);
      }
      canvas.drawCircle(activeLocation, thumbRadius, primaryPaint);
    }
  
negative.code: }
  
  const double _kThumbRadius = 6.0;
  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({
  