flame/doc/examples/nine_tile_box/lib/main.dart

import 'package:flame/components.dart';
import 'package:flame/game.dart';
import 'package:flutter/material.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();

  final game = MyGame();
  runApp(
    GameWidget(
      game: game,
    ),
  );
}

class MyGame extends Game {
  NineTileBox nineTileBox;

  @override
  Future<void> onLoad() async {
    final sprite = Sprite(await images.load('nine-box.png'));
    nineTileBox = NineTileBox(sprite, tileSize: 8, destTileSize: 24);
  }

  @override
  void render(Canvas canvas) {
    const length = 300.0;
    final boxSize = Vector2.all(length);
    final position = (size - boxSize) / 2;
    nineTileBox.draw(canvas, position, boxSize);
  }

  @override
  void update(double dt) {}
}