From 3a8e2464420f2b513f4f0d99cd7d64ab0eda9826 Mon Sep 17 00:00:00 2001
From: Kurtis Melby <kurt@melby.me>
Date: Sat, 28 Oct 2023 19:19:36 -0400
Subject: [PATCH] fix: Setting world on FlameGame camera setter (#2831)

# Description

Currently setting a new `FlameGame.camera` can cause `camera.world` to
no long match `game.world`, which I think it's safe to assume is never
desirable.

This PR sets the `camera.world` to the game's `world` when setting a new
Camera, this matches what happens when a new World is set on the game
(`world.camera` is set automatically).
---
 packages/flame/lib/src/game/flame_game.dart   |  4 ++
 packages/flame/test/game/flame_game_test.dart | 47 +++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/packages/flame/lib/src/game/flame_game.dart b/packages/flame/lib/src/game/flame_game.dart
index b98d4e97f09..9f18fe460c5 100644
--- a/packages/flame/lib/src/game/flame_game.dart
+++ b/packages/flame/lib/src/game/flame_game.dart
@@ -65,6 +65,9 @@ class FlameGame<W extends World> extends ComponentTreeRoot
   ///
   /// You don't have to add the CameraComponent to the tree after setting it
   /// here, it is done automatically.
+  ///
+  /// When setting the camera, if it doesn't already have a world it will be
+  /// set to match the game's world.
   CameraComponent get camera => _camera;
   set camera(CameraComponent newCameraComponent) {
     _camera.removeFromParent();
@@ -72,6 +75,7 @@ class FlameGame<W extends World> extends ComponentTreeRoot
     if (_camera.parent == null) {
       add(_camera);
     }
+    _camera.world ??= world;
   }
 
   CameraComponent _camera;
diff --git a/packages/flame/test/game/flame_game_test.dart b/packages/flame/test/game/flame_game_test.dart
index d5564d9f9d7..188d07f3c5f 100644
--- a/packages/flame/test/game/flame_game_test.dart
+++ b/packages/flame/test/game/flame_game_test.dart
@@ -215,6 +215,53 @@ void main() {
         );
       },
     );
+
+    group('world and camera', () {
+      testWithFlameGame(
+        'game world setter',
+        (game) async {
+          final newWorld = World();
+          game.world = newWorld;
+          expect(game.world, newWorld);
+          expect(game.camera.world, newWorld);
+        },
+      );
+
+      testWithFlameGame(
+        'game camera setter',
+        (game) async {
+          final newCamera = CameraComponent();
+          game.camera = newCamera;
+          expect(game.camera, newCamera);
+          expect(game.world, isNotNull);
+          expect(game.camera.world, game.world);
+        },
+      );
+
+      testWithFlameGame(
+        'game camera setter with another world',
+        (game) async {
+          final camera1 = game.camera;
+          final world1 = game.world;
+          expect(world1, isNotNull);
+          expect(camera1, isNotNull);
+
+          final camera2 = CameraComponent();
+          final world2 = World();
+          camera2.world = world2;
+
+          game.camera = camera2;
+          expect(game.camera, camera2);
+          expect(game.camera.world, world2);
+          expect(game.world, world1);
+
+          game.camera = camera1;
+          expect(game.camera, camera1);
+          expect(game.camera.world, world1);
+          expect(game.world, world1);
+        },
+      );
+    });
   });
 
   group('Render box attachment', () {