Arc progress bar challenge

main.dart

import 'dart:ui' as ui;
import 'dart:math' as math;

import 'package:flutter/material.dart';

final Color darkBlue = Color.fromARGB(255, 18, 32, 47);

void main() {
  runApp(HomePage());
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return  MaterialApp(
      theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: MyWidget(),
        ),
      ),
    );
  }
}

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  double percent = 0.5;

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Padding(
          padding: const EdgeInsets.all(24.0),
          child: CustomPaint(
            painter: MyPainter(
                percent: percent,
                fromAngle: 10.toRadian(),
                toAngle: 80.toRadian()
            ),
            size: Size(200, 200),
          ),
        ),
        SizedBox(
          height: 40,
        ),
        Text('Percent: ${percent.toStringAsFixed(2)}'),
        Slider(
            value: percent,
            onChanged: (newValue) {
              setState(() {
                percent = newValue;
              });
            })
      ],
    );
  }
}

class MyPainter extends CustomPainter {
  final double percent;
  final double fromAngle;
  final double toAngle;

  MyPainter({
    this.percent,
    this.fromAngle,
    this.toAngle,
  });

  @override
  void paint(Canvas canvas, Size size) {
    final rect = Rect.fromLTWH(0, 0, size.width, size.height);

    final gradient = ui.Gradient.sweep(
      Offset(size.width / 2, size.height / 2),
      [Colors.blue, Colors.red],
      [percent, percent],
      TileMode.mirror,
      fromAngle - 10.toRadian(),
      toAngle + 10.toRadian(),
      null,
    );

    final paint = Paint()
      ..shader = gradient
      ..strokeWidth = 20
      ..style = PaintingStyle.stroke
      ..strokeCap = StrokeCap.round;
    canvas.drawArc(rect, fromAngle, toAngle - fromAngle, false, paint);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) => false;
}

extension on int {
  double toRadian() => (this * math.pi) / 180.0;
}