Add game_template (#1180)

Adds a template / sample for games built in Flutter, with all the bells and whistles, like ads, in-app purchases, audio, main menu, settings, and so on.

Co-authored-by: Parker Lougheed
Co-authored-by: Shams Zakhour

game_template/lib/src/main_menu/main_menu_screen.dart

@@ -0,0 +1,123 @@
+// Copyright 2022, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:go_router/go_router.dart';
+import 'package:provider/provider.dart';
+
+import '../audio/audio_controller.dart';
+import '../audio/sounds.dart';
+import '../games_services/games_services.dart';
+import '../settings/settings.dart';
+import '../style/palette.dart';
+import '../style/responsive_screen.dart';
+
+class MainMenuScreen extends StatelessWidget {
+  const MainMenuScreen({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    final palette = context.watch<Palette>();
+    final gamesServicesController = context.watch<GamesServicesController?>();
+    final settingsController = context.watch<SettingsController>();
+    final audioController = context.watch<AudioController>();
+
+    return Scaffold(
+      backgroundColor: palette.backgroundMain,
+      body: ResponsiveScreen(
+        mainAreaProminence: 0.45,
+        squarishMainArea: Center(
+          child: Transform.rotate(
+            angle: -0.1,
+            child: const Text(
+              'Flutter Game Template!',
+              textAlign: TextAlign.center,
+              style: TextStyle(
+                fontFamily: 'Permanent Marker',
+                fontSize: 55,
+                height: 1,
+              ),
+            ),
+          ),
+        ),
+        rectangularMenuArea: Column(
+          mainAxisAlignment: MainAxisAlignment.end,
+          children: [
+            ElevatedButton(
+              onPressed: () {
+                audioController.playSfx(SfxType.buttonTap);
+                GoRouter.of(context).go('/play');
+              },
+              child: const Text('Play'),
+            ),
+            _gap,
+            if (gamesServicesController != null) ...[
+              _hideUntilReady(
+                ready: gamesServicesController.signedIn,
+                child: ElevatedButton(
+                  onPressed: () => gamesServicesController.showAchievements(),
+                  child: const Text('Achievements'),
+                ),
+              ),
+              _gap,
+              _hideUntilReady(
+                ready: gamesServicesController.signedIn,
+                child: ElevatedButton(
+                  onPressed: () => gamesServicesController.showLeaderboard(),
+                  child: const Text('Leaderboard'),
+                ),
+              ),
+              _gap,
+            ],
+            ElevatedButton(
+              onPressed: () => GoRouter.of(context).go('/settings'),
+              child: const Text('Settings'),
+            ),
+            _gap,
+            Padding(
+              padding: const EdgeInsets.only(top: 32),
+              child: ValueListenableBuilder<bool>(
+                valueListenable: settingsController.muted,
+                builder: (context, muted, child) {
+                  return IconButton(
+                    onPressed: () => settingsController.toggleMuted(),
+                    icon: Icon(muted ? Icons.volume_off : Icons.volume_up),
+                  );
+                },
+              ),
+            ),
+            _gap,
+            const Text('Music by Mr Smith'),
+            _gap,
+          ],
+        ),
+      ),
+    );
+  }
+
+  /// Prevents the game from showing game-services-related menu items
+  /// until we're sure the player is signed in.
+  ///
+  /// This normally happens immediately after game start, so players will not
+  /// see any flash. The exception is folks who decline to use Game Center
+  /// or Google Play Game Services, or who haven't yet set it up.
+  Widget _hideUntilReady({required Widget child, required Future<bool> ready}) {
+    return FutureBuilder<bool>(
+      future: ready,
+      builder: (context, snapshot) {
+        // Use Visibility here so that we have the space for the buttons
+        // ready.
+        return Visibility(
+          visible: snapshot.data ?? false,
+          maintainState: true,
+          maintainSize: true,
+          maintainAnimation: true,
+          child: child,
+        );
+      },
+    );
+  }
+
+  static const _gap = SizedBox(height: 10);
+}