From eb4fc09d83fdfe235d658b30de5e19c110526d4c Mon Sep 17 00:00:00 2001
From: Adil Hanney <adilhanney@disroot.org>
Date: Tue, 8 Aug 2023 19:50:07 +0100
Subject: [PATCH] fix: Pause forge2d when backgrounded

---
 .github/.cspell/gamedev_dictionary.txt        |  2 +
 .../flame/lib/src/game/game_render_box.dart   | 10 ++++-
 packages/flame_forge2d/lib/forge2d_game.dart  | 41 +++++++++++++++++++
 .../flame_forge2d/test/forge2d_game_test.dart | 29 +++++++++++++
 4 files changed, 80 insertions(+), 2 deletions(-)

diff --git a/.github/.cspell/gamedev_dictionary.txt b/.github/.cspell/gamedev_dictionary.txt
index 5cd7da96f94..09b55065806 100644
--- a/.github/.cspell/gamedev_dictionary.txt
+++ b/.github/.cspell/gamedev_dictionary.txt
@@ -22,6 +22,7 @@ arial
 arities
 arity
 autofocus
+backgrounded
 backpressure
 backquote
 backtick
@@ -51,6 +52,7 @@ drawables
 easings
 flippable
 focusable
+foregrounded
 fullscreen
 gamepad
 gamepads
diff --git a/packages/flame/lib/src/game/game_render_box.dart b/packages/flame/lib/src/game/game_render_box.dart
index 64d4f9401a2..d6f245f43db 100644
--- a/packages/flame/lib/src/game/game_render_box.dart
+++ b/packages/flame/lib/src/game/game_render_box.dart
@@ -131,11 +131,17 @@ class GameRenderBox extends RenderBox with WidgetsBindingObserver {
   }
 
   void _bindLifecycleListener() {
-    _ambiguate(WidgetsBinding.instance)!.addObserver(this);
+    final binding = _ambiguate(WidgetsBinding.instance)!;
+    binding.addObserver(this);
+    didChangeAppLifecycleState(
+      binding.lifecycleState ?? AppLifecycleState.resumed,
+    );
   }
 
   void _unbindLifecycleListener() {
-    _ambiguate(WidgetsBinding.instance)!.removeObserver(this);
+    final binding = _ambiguate(WidgetsBinding.instance)!;
+    binding.removeObserver(this);
+    didChangeAppLifecycleState(AppLifecycleState.paused);
   }
 
   @override
diff --git a/packages/flame_forge2d/lib/forge2d_game.dart b/packages/flame_forge2d/lib/forge2d_game.dart
index 40eb86bbcb1..45424bd6afb 100644
--- a/packages/flame_forge2d/lib/forge2d_game.dart
+++ b/packages/flame_forge2d/lib/forge2d_game.dart
@@ -1,5 +1,6 @@
 import 'package:flame/game.dart';
 import 'package:flame_forge2d/world_contact_listener.dart';
+import 'package:flutter/material.dart';
 import 'package:forge2d/forge2d.dart';
 
 class Forge2DGame extends FlameGame {
@@ -8,6 +9,7 @@ class Forge2DGame extends FlameGame {
     double zoom = defaultZoom,
     Camera? camera,
     ContactListener? contactListener,
+    this.pauseWhenBackgrounded = false,
   })  : world = World(gravity ?? defaultGravity),
         super(camera: camera ?? Camera()) {
     // ignore: deprecated_member_use
@@ -21,6 +23,14 @@ class Forge2DGame extends FlameGame {
 
   final World world;
 
+  /// Whether the game should pause when the app is backgrounded.
+  ///
+  /// If true, the first update after the app is foregrounded will be skipped.
+  ///
+  /// Defaults to false.
+  bool pauseWhenBackgrounded;
+  bool _pausedBecauseBackgrounded = false;
+
   @override
   void update(double dt) {
     super.update(dt);
@@ -38,4 +48,35 @@ class Forge2DGame extends FlameGame {
   Vector2 screenToFlameWorld(Vector2 position) {
     return screenToWorld(position)..y *= -1;
   }
+
+  @override
+  @mustCallSuper
+  void lifecycleStateChange(AppLifecycleState state) {
+    switch (state) {
+      case AppLifecycleState.resumed:
+      case AppLifecycleState.inactive:
+        if (_pausedBecauseBackgrounded) {
+          resumeEngine();
+        }
+      case AppLifecycleState.paused:
+      case AppLifecycleState.detached:
+      case AppLifecycleState.hidden:
+        if (pauseWhenBackgrounded) {
+          pauseEngine();
+          _pausedBecauseBackgrounded = true;
+        }
+    }
+  }
+
+  @override
+  void pauseEngine() {
+    _pausedBecauseBackgrounded = false;
+    super.pauseEngine();
+  }
+
+  @override
+  void resumeEngine() {
+    _pausedBecauseBackgrounded = false;
+    super.resumeEngine();
+  }
 }
diff --git a/packages/flame_forge2d/test/forge2d_game_test.dart b/packages/flame_forge2d/test/forge2d_game_test.dart
index 727986a9095..f302ffd84d9 100644
--- a/packages/flame_forge2d/test/forge2d_game_test.dart
+++ b/packages/flame_forge2d/test/forge2d_game_test.dart
@@ -1,3 +1,5 @@
+import 'dart:ui' show AppLifecycleState;
+
 import 'package:flame_forge2d/flame_forge2d.dart';
 import 'package:test/test.dart';
 
@@ -50,4 +52,31 @@ void main() {
       });
     },
   );
+
+  group('pauseWhenBackgrounded:', () {
+    test('true', () async {
+      final game = Forge2DGame(
+        pauseWhenBackgrounded: true,
+      );
+
+      game.lifecycleStateChange(AppLifecycleState.paused);
+      expect(game.paused, true);
+
+      game.lifecycleStateChange(AppLifecycleState.resumed);
+      expect(game.paused, false);
+    });
+
+    test('false', () async {
+      final game = Forge2DGame(
+        // ignore: avoid_redundant_argument_values
+        pauseWhenBackgrounded: false,
+      );
+
+      game.lifecycleStateChange(AppLifecycleState.paused);
+      expect(game.paused, false);
+
+      game.lifecycleStateChange(AppLifecycleState.resumed);
+      expect(game.paused, false);
+    });
+  });
 }