如何在Flutter中绘制带有圆角矩形轨迹的滑块？

import 'package:flutter/material.dart';

class RoundedSlider extends StatefulWidget {
  @override
  _RoundedSliderState createState() => _RoundedSliderState();
}

class _RoundedSliderState extends State<RoundedSlider> {
  double _value = 0.0;

  @override
  Widget build(BuildContext context) {
    return SliderTheme(
      data: SliderTheme.of(context).copyWith(
        trackShape: RoundedRectSliderTrackShape(),
        trackHeight: 4.0,
        thumbShape: RoundSliderThumbShape(enabledThumbRadius: 12.0),
        overlayShape: RoundSliderOverlayShape(overlayRadius: 20.0),
      ),
      child: Slider(
        value: _value,
        onChanged: (newValue) {
          setState(() {
            _value = newValue;
          });
        },
      ),
    );
  }
}

class RoundedRectSliderTrackShape extends SliderTrackShape {
  Rect getPreferredRect({
    @required RenderBox parentBox,
    Offset offset = Offset.zero,
    @required SliderThemeData sliderTheme,
    bool isEnabled = false,
    bool isDiscrete = false,
  }) {
    final double trackHeight = sliderTheme.trackHeight;
    final double trackLeft = offset.dx + 10.0;
    final double trackTop = offset.dy + (parentBox.size.height - trackHeight) / 2;
    final double trackWidth = parentBox.size.width - 20.0;
    return Rect.fromLTWH(trackLeft, trackTop, trackWidth, trackHeight);
  }
}

class RoundSliderThumbShape extends SliderComponentShape {
  final double enabledThumbRadius;

  const RoundSliderThumbShape({
    this.enabledThumbRadius = 10.0,
  });

  Size getPreferredSize(bool isEnabled, bool isDiscrete) {
    return Size.fromRadius(enabledThumbRadius);
  }

  void paint(
    PaintingContext context,
    Offset center, {
    Animation<double> activationAnimation,
    Animation<double> enableAnimation,
    bool isDiscrete,
    TextPainter labelPainter,
    RenderBox parentBox,
    SliderThemeData sliderTheme,
    TextDirection textDirection,
    double value,
  }) {
    final Canvas canvas = context.canvas;
    final Paint paint = Paint()
      ..color = sliderTheme.thumbColor
      ..style = PaintingStyle.fill;
    canvas.drawCircle(center, enabledThumbRadius, paint);
  }
}

class RoundSliderOverlayShape extends SliderComponentShape {
  final double overlayRadius;

  const RoundSliderOverlayShape({
    this.overlayRadius = 20.0,
  });

  Size getPreferredSize(bool isEnabled, bool isDiscrete) {
    return Size.fromRadius(overlayRadius);
  }

  void paint(
    PaintingContext context,
    Offset center, {
    Animation<double> activationAnimation,
    Animation<double> enableAnimation,
    bool isDiscrete,
    TextPainter labelPainter,
    RenderBox parentBox,
    SliderThemeData sliderTheme,
    TextDirection textDirection,
    double value,
  }) {
    final Canvas canvas = context.canvas;
    final Paint paint = Paint()
      ..color = sliderTheme.overlayColor
      ..style = PaintingStyle.fill;
    canvas.drawCircle(center, overlayRadius, paint);
  }
}