Custom painer with hole inside

transparent_rounded_rectangle.dart

import 'package:flutter/material.dart';

class TransparentRoundedRectangle extends StatelessWidget {
  const TransparentRoundedRectangle({super.key});

  @override
  Widget build(BuildContext context) {
    return CustomPaint(
      painter: CandlePainter(),
    );
  }
}

class CandlePainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    Paint paint = Paint()
      ..color = Colors.orange;

    canvas.drawPath(
      Path.combine(
        PathOperation.difference,
        Path()..addRect(Rect.fromLTRB(0, 0, size.width, size.height)),
        Path()
          ..addRRect(RRect.fromLTRBR(
              0, 0, size.width, size.height, Radius.circular(30)))
          ..close(),
      ),
      paint,
    );
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) {
    return false;
  }
}