Calibration Page

calibration_screen.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  
  void _reporter(Offset global, Offset center) {
    print( 'Touch: Global -> $global, Local -> $center');
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        canvasColor: Colors.white,
      ),
      home: Material(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          children: <Widget>[
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: <Widget>[
                CalibrationPoint(reporter: _reporter),
                CalibrationPoint(reporter: _reporter),
              ],
            ),
            Container(             
              alignment: Alignment.center,
              child: CalibrationPoint(reporter: _reporter),
            ),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: <Widget>[
                CalibrationPoint(reporter: _reporter),
                CalibrationPoint(reporter: _reporter),
              ],
            ),
          ],
        ),
      ),
    );
  }
}

typedef ReportCalibration = void Function(Offset global, Offset center);

class CalibrationPoint extends StatelessWidget {
  const CalibrationPoint({
    Key key,
    @required this.reporter,
   }) : super(key: key);

  final ReportCalibration reporter;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      behavior: HitTestBehavior.opaque,
      onTapDown: (details) => _handleTapDown(context, details),
      child: Padding(
        padding: const EdgeInsets.all(50.0),
        child: Icon(Icons.add),
      ),
    );
  }

  void _handleTapDown(BuildContext context, TapDownDetails details) {
    final RenderBox renderBox = context.findRenderObject();
    final centerPos = renderBox.localToGlobal(renderBox.size.center(Offset.zero));
    reporter(details.globalPosition, centerPos);
  }
}