[Flutter]ちょっと座標指定しやすく

真ん中が原点だし、経度緯度では指定しにくいのでちょっと変更。

import 'package:flutter/material.dart';
import 'package:flutter_map/flutter_map.dart';
import 'package:latlong2/latlong.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return FlutterMap(
      options: MapOptions(
        crs: CrsSimple(),
        center: LatLng(-0.5, 0.5),
        zoom: 1.5,
        maxZoom: 3.0,
      ),
      layers: [
        TileLayerOptions(
          tileProvider: const AssetTileProvider(),
          urlTemplate: "assets/tempest/{z}/{x}/{y}.jpg",
          attributionBuilder: (_) {
            return const Text(
              '©2010-2021 SQUARE ENIX CO., LTD. All Rights Reserved.',
              style: TextStyle(
                fontSize: 10,
                backgroundColor: Colors.white,
              ),
            );
          },
        ),
        MarkerLayerOptions(
          markers: [
            Marker(
              width: 25.0,
              height: 25.0,
              point: LatLng(-(1 / 409 * (174 - 10)),
                  (1 / 409 * (326 - 10))), // 1で一番端っこ(y, x)
              builder: (ctx) => Image.asset('assets/aetheryte.png'),
            ),
            Marker(
              width: 25.0,
              height: 25.0,
              point: LatLng(-(1 / 409 * (258 - 10)),
                  (1 / 409 * (185 - 10))), // 1で一番端っこ(y, x)
              builder: (ctx) => Image.asset('assets/aetheryte.png'),
            ),
          ],
        ),
      ],
    );
  }
}

crs: CrsSimple()追加したら左上が原点になりました。
そして右下がLatLng(-1, 1)。