twonly-app/lib/src/views/camera/painters/barcode_detector_painter.dart

import 'dart:ui';
import 'package:camera/camera.dart';
import 'package:flutter/material.dart';
import 'package:google_mlkit_barcode_scanning/google_mlkit_barcode_scanning.dart';
import 'coordinates_translator.dart';

class BarcodeDetectorPainter extends CustomPainter {
  BarcodeDetectorPainter(
    this.barcodes,
    this.imageSize,
    this.rotation,
    this.cameraLensDirection,
  );

  final List<Barcode> barcodes;
  final Size imageSize;
  final InputImageRotation rotation;
  final CameraLensDirection cameraLensDirection;

  @override
  void paint(Canvas canvas, Size size) {
    final paint = Paint()
      ..style = PaintingStyle.stroke
      ..strokeWidth = 3.0
      ..color = Colors.lightGreenAccent;

    for (final barcode in barcodes) {
      final cornerPoints = <Offset>[];
      for (final point in barcode.cornerPoints) {
        final x = translateX(
          point.x.toDouble(),
          size,
          imageSize,
          rotation,
          cameraLensDirection,
        );
        final y = translateY(
          point.y.toDouble(),
          size,
          imageSize,
          rotation,
          cameraLensDirection,
        );

        cornerPoints.add(Offset(x, y));
      }

      cornerPoints.add(cornerPoints.first);
      canvas.drawPoints(PointMode.polygon, cornerPoints, paint);
    }
  }

  @override
  bool shouldRepaint(BarcodeDetectorPainter oldDelegate) {
    return oldDelegate.imageSize != imageSize ||
        oldDelegate.barcodes != barcodes;
  }
}