Path + Positioned Widgets

main.dart

import 'dart:math' show Random;
import 'package:flutter/material.dart';

List<bool> checkmarks = List.generate(10, (_) => false);

void main() {
  runApp(
    MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Demo',
      home: HomePage(),
    ),
  );
}

class HomePage extends StatefulWidget {
  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    double checkBoxSize = computeCheckBoxSize(context);
    return Scaffold(
      body: LayoutBuilder(
        builder: (context, constraints) {
          final height = constraints.biggest.height;
          final width = constraints.biggest.width;
          return Stack(
            children: [
              Container(color: Colors.amber.shade100),
              Positioned.fill(child: CustomPaint(painter: TestPathPainter())),
              ...points.indexed
                  .map(
                    (point) => Positioned(
                      left: point.$2.dx * width - checkBoxSize / 2,
                      top: point.$2.dy * height - checkBoxSize / 2,
                      child: Checkbox(
                        value: checkmarks[point.$1],
                        onChanged: (_) {
                          setState(() {
                            checkmarks[point.$1] = !checkmarks[point.$1];
                          });
                        },
                      ),
                    ),
                  )
                  .toList(),
            ],
          );
        },
      ),
    );
  }
}

double computeCheckBoxSize(BuildContext context) {
  final ThemeData themeData = Theme.of(context);
  final MaterialTapTargetSize effectiveMaterialTapTargetSize =
      themeData.checkboxTheme.materialTapTargetSize ??
          themeData.materialTapTargetSize;
  final VisualDensity effectiveVisualDensity =
      themeData.checkboxTheme.visualDensity ?? themeData.visualDensity;
  Size size;
  switch (effectiveMaterialTapTargetSize) {
    case MaterialTapTargetSize.padded:
      size = const Size(kMinInteractiveDimension, kMinInteractiveDimension);
      break;
    case MaterialTapTargetSize.shrinkWrap:
      size = const Size(
          kMinInteractiveDimension - 8.0, kMinInteractiveDimension - 8.0);
      break;
  }
  size += effectiveVisualDensity.baseSizeAdjustment;
  return size.longestSide;
}

class TestPathPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final paint = Paint()
      ..style = PaintingStyle.stroke
      ..strokeWidth = 2.0
      ..color = Colors.black;

    final path = Path()
      ..moveTo(
        points[0].dx * size.width,
        points[0].dy * size.height,
      );
    points.sublist(1).forEach(
          (point) => path.lineTo(
            point.dx * size.width,
            point.dy * size.height,
          ),
        );
    canvas.drawPath(path, paint);
  }

  @override
  bool shouldRepaint(TestPathPainter oldDelegate) => false;
}

final random = Random();
final List<Offset> points = List.generate(
  10,
  (index) => Offset(.1 + random.nextDouble() * .8, .1 + index * .8 / 9),
);