DashLinePainter.dart

class DashLinePainter extends CustomPainter {
  final double progress;

  DashLinePainter({this.progress});

  Paint _paint = Paint()
    ..color = Colors.black
    ..strokeWidth = 4.0
    ..style = PaintingStyle.stroke
    ..strokeJoin = StrokeJoin.round;

  @override
  void paint(Canvas canvas, Size size) {
    var path = Path()
      ..moveTo(0, size.height / 2)
      ..lineTo(size.width * progress, size.height / 2);

    Path dashPath = Path();

    double dashWidth = 10.0;
    double dashSpace = 5.0;
    double distance = 0.0;

    for (PathMetric pathMetric in path.computeMetrics()) {
      while (distance < pathMetric.length) {
        dashPath.addPath(
          pathMetric.extractPath(distance, distance + dashWidth),
          Offset.zero,
        );
        distance += dashWidth;
        distance += dashSpace;
      }
    }
    canvas.drawPath(dashPath, _paint);
  }

  @override
  bool shouldRepaint(DashLinePainter oldDelegate) {
    return oldDelegate.progress != progress;
  }
}