anchor.diff:    void paint(Canvas canvas, Size size) {
       Paint paint = new Paint()
         ..color = backgroundColor
  -      ..style = PaintingStyle.fill;
  +      ..style = ui.PaintingStyle.fill;
       canvas.drawRect(Point.origin & size, paint);
   
       paint.color = valueColor;
  
positive.code:   const _CircularProgressIndicatorPainter({
      this.valueColor,
      this.value,
      this.animationValue
    });
  
    final Color valueColor;
    final double value;
    final double animationValue;
  
    void paint(Canvas canvas, Size size) {
      Paint paint = new Paint()
        ..color = valueColor
        ..strokeWidth = _kCircularProgressIndicatorStrokeWidth
        ..style = PaintingStyle.stroke;
  
      if (value != null) {
        double angle = value.clamp(0.0, 1.0) * _kSweep;
        Path path = new Path()
          ..arcTo(Point.origin & size, _kStartAngle, angle, false);
        canvas.drawPath(path, paint);
      } else {
        double startAngle = _kTwoPI * (1.75 * animationValue - 0.75);
        double endAngle = startAngle + _kTwoPI * 0.75;
        double arcAngle = startAngle.clamp(0.0, _kTwoPI);
        double arcSweep = endAngle.clamp(0.0, _kTwoPI) - arcAngle;
        Path path = new Path()
          ..arcTo(Point.origin & size, _kStartAngle + arcAngle, arcSweep, false);
        canvas.drawPath(path, paint);
      }
    }
  
negative.code: // found in the LICENSE file.
  
  import 'dart:math' as math;
  import 'dart:ui' as ui;
  
  import 'package:flutter/animation.dart';
  import 'package:flutter/widgets.dart';
  
  import 'theme.dart';
  
  const double _kLinearProgressIndicatorHeight = 6.0;
  const double _kMinCircularProgressIndicatorSize = 36.0;
  const double _kCircularProgressIndicatorStrokeWidth = 4.0;
  
  // TODO(hansmuller) implement the support for buffer indicator
  
  