example

a.dart

import 'package:flutter/material.dart';
import 'package:flutter_svg/flutter_svg.dart';
import 'package:mobile_scanner/mobile_scanner.dart';
import 'package:sco_mobile/constants/colors.dart';

typedef MobileScannerErrorBuilder = Widget Function(
  BuildContext,
  MobileScannerException,
  Widget?,
);

class ScannerScreen extends StatefulWidget {
  const ScannerScreen({Key? key}) : super(key: key);

  @override
  ScannerScreenState createState() => ScannerScreenState();
}

class ScannerScreenState extends State<ScannerScreen> {
  MobileScannerController cameraController = MobileScannerController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text(''),
        backgroundColor: Colors.transparent,
        elevation: 0.0,
        leading: IconButton(
          icon: SvgPicture.asset(
            'assets/images/icons/ArrowLeft.svg',
            colorFilter: const ColorFilter.mode(
              NeutralColor.n0,
              BlendMode.srcIn,
            ),
          ),
          onPressed: () => Navigator.of(context).pop(),
        ),
        actions: [
          IconButton(
            icon: ValueListenableBuilder(
              valueListenable: cameraController.torchState,
              builder: (context, state, child) {
                return SvgPicture.asset(
                  state == TorchState.on
                      ? 'assets/images/icons/smile.svg'
                      : 'assets/images/icons/perfil.svg',
                  colorFilter: const ColorFilter.mode(
                    NeutralColor.n0,
                    BlendMode.srcIn,
                  ),
                );
              },
            ),
            onPressed: () => cameraController.toggleTorch(),
          ),
          IconButton(
            icon: ValueListenableBuilder(
              valueListenable: cameraController.cameraFacingState,
              builder: (context, state, child) {
                return SvgPicture.asset(
                  state == CameraFacing.front
                      ? 'assets/images/icons/Eye.svg'
                      : 'assets/images/icons/EyeSlash.svg',
                  colorFilter: const ColorFilter.mode(
                    NeutralColor.n0,
                    BlendMode.srcIn,
                  ),
                );
              },
            ),
            onPressed: () => cameraController.switchCamera(),
          ),
        ],
      ),
      extendBodyBehindAppBar: true,
      body: Stack(
        children: [
          MobileScanner(
            controller: cameraController,
            errorBuilder:(context,exception,widget){
            print(exception);
            return Center(child:Text(exception.toString()));
            }
            ,
            onDetect: (capture) {
              final List<Barcode> barcodes = capture.barcodes;
              for (final barcode in barcodes) {
                debugPrint('Barcode found >>>>> ${barcode.rawValue} <<<<<');
              }
            },
          ),
          _buildOverlay(MediaQuery.of(context).size),
        ],
      ),
    );
  }
}

class InvertedClipper extends CustomClipper<Path> {
  final Rect cutOutRect;

  InvertedClipper(this.cutOutRect);

  @override
  Path getClip(Size size) {
    final path = Path()
      ..addRect(Rect.fromLTWH(0, 0, size.width, size.height))
      ..addRect(cutOutRect);
    path.fillType = PathFillType.evenOdd;
    return path;
  }

  @override
  bool shouldReclip(InvertedClipper oldClipper) =>
      oldClipper.cutOutRect != cutOutRect;
}

Widget _buildOverlay(Size size) {
  final cutOutRect = Rect.fromLTWH(
    16,
    (size.height - 208) / 2,
    size.width - 32,
    208,
  );

  return ClipPath(
    clipper: InvertedClipper(cutOutRect),
    child: Container(
      color: NeutralColor.n700.withOpacity(0.9),
    ),
  );
}