fix: Use root game for gestures (#2756)

Since registering detectors won't work on a non-root game we have to register the dispatchers on the root game.

packages/flame/lib/src/components/core/component.dart

@@ -381,6 +381,8 @@ class Component {
 
   @internal
   static Game? staticGameInstance;
+
+  /// Fetches the nearest [FlameGame] ancestor to the component.
   FlameGame? findGame() {
     assert(
       staticGameInstance is FlameGame || staticGameInstance == null,
@@ -393,6 +395,15 @@ class Component {
         ((this is FlameGame) ? (this as FlameGame) : _parent?.findGame());
   }
 
+  /// Fetches the root [FlameGame] ancestor to the component.
+  FlameGame? findRootGame() {
+    var game = findGame();
+    while (game?.parent != null) {
+      game = game!.parent!.findGame();
+    }
+    return game;
+  }
+
   /// Whether the children list contains the given component.
   ///
   /// This method uses reference equality.

packages/flame/lib/src/events/component_mixins/double_tap_callbacks.dart

@@ -28,7 +28,7 @@ mixin DoubleTapCallbacks on Component {
   @override
   void onMount() {
     super.onMount();
-    final game = findGame()!;
+    final game = findRootGame()!;
     if (game.findByKey(const DoubleTapDispatcherKey()) == null) {
       final dispatcher = DoubleTapDispatcher();
       game.registerKey(const DoubleTapDispatcherKey(), dispatcher);

packages/flame/lib/src/events/component_mixins/drag_callbacks.dart

@@ -65,7 +65,7 @@ mixin DragCallbacks on Component {
   @mustCallSuper
   void onMount() {
     super.onMount();
-    final game = findGame()!;
+    final game = findRootGame()!;
     if (game.findByKey(const MultiDragDispatcherKey()) == null) {
       final dispatcher = MultiDragDispatcher();
       game.registerKey(const MultiDragDispatcherKey(), dispatcher);

packages/flame/lib/src/events/component_mixins/pointer_move_callbacks.dart

@@ -18,7 +18,7 @@ mixin PointerMoveCallbacks on Component {
   }
 
   static void onMountHandler(PointerMoveCallbacks instance) {
-    final game = instance.findGame()!;
+    final game = instance.findRootGame()!;
     const key = MouseMoveDispatcherKey();
     if (game.findByKey(key) == null) {
       final dispatcher = PointerMoveDispatcher();

packages/flame/lib/src/events/component_mixins/tap_callbacks.dart

@@ -22,7 +22,7 @@ mixin TapCallbacks on Component {
   @mustCallSuper
   void onMount() {
     super.onMount();
-    final game = findGame()!;
+    final game = findRootGame()!;
     if (game.findByKey(const MultiTapDispatcherKey()) == null) {
       final dispatcher = MultiTapDispatcher();
       game.registerKey(const MultiTapDispatcherKey(), dispatcher);

packages/flame/test/components/component_test.dart

@@ -1121,6 +1121,28 @@ void main() {
       });
     });
 
+    group('findRootGame()', () {
+      testWithFlameGame('finds root game in nested game structure',
+          (game) async {
+        final component = Component();
+        await game.ensureAdd(
+          FlameGame(
+            children: [
+              Component(children: [component]),
+            ],
+          ),
+        );
+        expect(component.findRootGame(), game);
+      });
+
+      testWithFlameGame('finds root game in non-nested game structure',
+          (game) async {
+        final component = Component();
+        await game.ensureAdd(component);
+        expect(component.findRootGame(), game);
+      });
+    });
+
     group('miscellaneous', () {
       testWithFlameGame('childrenFactory', (game) async {
         final component0 = Component();