CircularProgressBorder flutter widget

circular_progress_border.dart

import 'package:flutter/material.dart';
import 'dart:math';

class CircularProgressBorder extends StatelessWidget {
  final Color backgroundColor;
  final Color progressColor;
  final Color unfilledColor;
  final double progress;
  final double thickness;
  final double offset;
  final Widget child;

  const CircularProgressBorder({
    Key key,
    @required this.child,
    @required this.progressColor,
    @required this.progress,
    this.backgroundColor = Colors.white,
    this.offset = 0,
    this.thickness = 2,
    this.unfilledColor = Colors.transparent,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final tau = 2 * pi;
    return Stack(
      children: [
        Positioned.fill(
          child: ShaderMask(
            shaderCallback: (rect) {
              return SweepGradient(
                  startAngle: 0,
                  endAngle: tau,
                  transform: GradientRotation(offset * tau),
                  stops: [progress, progress],
                  center: Alignment.center,
                  colors: [
                    progressColor,
                    unfilledColor,
                  ]).createShader(rect);
            },
            child: Container(
              decoration: const BoxDecoration(
                  shape: BoxShape.circle, color: Colors.white),
            ),
          ),
        ),
        Positioned.fill(
          left: thickness,
          top: thickness,
          right: thickness,
          bottom: thickness,
          child: FractionallySizedBox(
              heightFactor: 1,
              child: Container(
                clipBehavior: Clip.hardEdge,
                decoration: const BoxDecoration(
                    shape: BoxShape.circle, color: Colors.white),
                child: Center(
                  child: child,
                ),
              )),
        ),
      ],
    );
  }
}