feat: Add DoubleTapCallbacks that receives double-tap events.

doc/flame/inputs/gesture_input.md

@@ -473,6 +473,31 @@ class MyGame extends FlameGame with HasHoverables {
 ```
 
 
+### DoubleTapCallbacks
+
+Flame also offers a mixin named `DoubleTapCallbacks` to receive a double-tap event from the
+component. To start receiving double tap events in a component, add the
+`DoubleTapCallbacks` mixin to your `PositionComponent`.
+
+```dart
+class MyComponent extends PositionComponent with DoubleTapCallbacks {
+  @override
+  void onDoubleTapUp(DoubleTapEvent event) {
+    /// Do something
+  }
+
+  @override
+  void onDoubleTapCancel(DoubleTapCancelEvent event) {
+    /// Do something
+  }
+
+  @override
+  void onDoubleTapDown(DoubleTapDownEvent event) {
+    /// Do something
+  }
+```
+
+
 ### GestureHitboxes
 
 The `GestureHitboxes` mixin is used to more accurately recognize gestures on top of your

examples/lib/stories/input/double_tap_callbacks_example.dart

@@ -0,0 +1,65 @@
+import 'package:examples/commons/ember.dart';
+import 'package:flame/components.dart';
+import 'package:flame/experimental.dart';
+import 'package:flame/game.dart';
+import 'package:flutter/material.dart';
+
+class DoubleTapCallbacksExample extends FlameGame with DoubleTapCallbacks {
+  static const String description = '''
+  In this example, we show how you can use the `DoubleTapCallbacks` mixin on
+  a `Component`. Double tap Ember and see her color changing.
+  The example also adds white circles when double-tapping on the game area.
+''';
+
+  @override
+  Future<void> onLoad() async {
+    children.register<DoubleTappableEmber>();
+  }
+
+  @override
+  void onGameResize(Vector2 canvasSize) {
+    children
+        .query<DoubleTappableEmber>()
+        .forEach((element) => element.removeFromParent());
+    add(DoubleTappableEmber(position: canvasSize / 2));
+
+    super.onGameResize(canvasSize);
+  }
+
+  @override
+  void onDoubleTapDown(DoubleTapDownEvent event) {
+    add(
+      CircleComponent(
+        radius: 30,
+        position: event.localPosition,
+        anchor: Anchor.center,
+      ),
+    );
+  }
+}
+
+class DoubleTappableEmber extends Ember with DoubleTapCallbacks {
+  @override
+  bool debugMode = true;
+
+  DoubleTappableEmber({Vector2? position})
+      : super(
+          position: position ?? Vector2.all(100),
+          size: Vector2.all(100),
+        );
+
+  @override
+  void onDoubleTapUp(DoubleTapEvent event) {
+    debugColor = Colors.greenAccent;
+  }
+
+  @override
+  void onDoubleTapCancel(DoubleTapCancelEvent event) {
+    debugColor = Colors.red;
+  }
+
+  @override
+  void onDoubleTapDown(DoubleTapDownEvent event) {
+    debugColor = Colors.blue;
+  }
+}

examples/lib/stories/input/input.dart

@@ -1,5 +1,6 @@
 import 'package:dashbook/dashbook.dart';
 import 'package:examples/commons/commons.dart';
+import 'package:examples/stories/input/double_tap_callbacks_example.dart';
 import 'package:examples/stories/input/draggables_example.dart';
 import 'package:examples/stories/input/gesture_hitboxes_example.dart';
 import 'package:examples/stories/input/hardware_keyboard_example.dart';
@@ -38,6 +39,16 @@ void addInputStories(Dashbook dashbook) {
       codeLink: baseLink('input/draggables_example.dart'),
       info: DraggablesExample.description,
     )
+    ..add(
+      'Double Tap (Component)',
+      (context) {
+        return GameWidget(
+          game: DoubleTapCallbacksExample(),
+        );
+      },
+      codeLink: baseLink('input/draggables_example.dart'),
+      info: DoubleTapCallbacksExample.description,
+    )
     ..add(
       'Hoverables',
       (_) => GameWidget(game: HoverablesExample()),

packages/flame/lib/experimental.dart

@@ -21,6 +21,8 @@ export 'src/camera/viewports/fixed_aspect_ratio_viewport.dart'
 export 'src/camera/viewports/fixed_size_viewport.dart' show FixedSizeViewport;
 export 'src/camera/viewports/max_viewport.dart' show MaxViewport;
 export 'src/camera/world.dart' show World;
+export 'src/events/component_mixins/double_tap_callbacks.dart'
+    show DoubleTapCallbacks;
 export 'src/events/component_mixins/drag_callbacks.dart' show DragCallbacks;
 export 'src/events/component_mixins/tap_callbacks.dart' show TapCallbacks;
 export 'src/events/flame_game_mixins/has_draggable_components.dart'
@@ -32,6 +34,10 @@ export 'src/events/flame_game_mixins/has_tappable_components.dart'
     show HasTappableComponents;
 export 'src/events/flame_game_mixins/has_tappables_bridge.dart'
     show HasTappablesBridge;
+export 'src/events/messages/double_tap_cancel_event.dart'
+    show DoubleTapCancelEvent;
+export 'src/events/messages/double_tap_down_event.dart' show DoubleTapDownEvent;
+export 'src/events/messages/double_tap_event.dart' show DoubleTapEvent;
 export 'src/events/messages/drag_cancel_event.dart' show DragCancelEvent;
 export 'src/events/messages/drag_end_event.dart' show DragEndEvent;
 export 'src/events/messages/drag_start_event.dart' show DragStartEvent;

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

@@ -0,0 +1,37 @@
+import 'package:flame/game.dart';
+import 'package:flame/src/components/core/component.dart';
+import 'package:flame/src/events/flame_game_mixins/double_tap_dispatcher.dart';
+import 'package:flame/src/events/messages/double_tap_cancel_event.dart';
+import 'package:flame/src/events/messages/double_tap_down_event.dart';
+import 'package:flame/src/events/messages/double_tap_event.dart';
+
+/// [DoubleTapCallbacks] adds the ability to receive double-tap events in a
+/// component.
+///
+/// In addition to adding this mixin, the component must also implement the
+/// [containsLocalPoint] method.
+///
+/// At present, flutter detects only one double-tap events simultaneously.
+/// This means that if you're double-tapping two [DoubleTapCallbacks] located
+/// far away from each other, only one callback will be fired (or none).
+mixin DoubleTapCallbacks on Component {
+  /// This triggers when the pointer stops contacting the device after the
+  /// second tap.
+  void onDoubleTapUp(DoubleTapEvent event) {}
+
+  /// This triggers immediately after the down event of the second tap.
+  void onDoubleTapDown(DoubleTapDownEvent event) {}
+
+  /// This triggers once the gesture loses the arena if [onDoubleTapDown] has
+  /// previously been triggered.
+  void onDoubleTapCancel(DoubleTapCancelEvent event) {}
+
+  @override
+  void onMount() {
+    super.onMount();
+    final game = findGame()! as FlameGame;
+    if (game.firstChild<DoubleTapDispatcher>() == null) {
+      game.add(DoubleTapDispatcher());
+    }
+  }
+}

packages/flame/lib/src/events/flame_game_mixins/double_tap_dispatcher.dart

@@ -0,0 +1,66 @@
+import 'package:flame/components.dart';
+import 'package:flame/game.dart';
+import 'package:flame/src/events/component_mixins/double_tap_callbacks.dart';
+import 'package:flame/src/events/messages/double_tap_cancel_event.dart';
+import 'package:flame/src/events/messages/double_tap_down_event.dart';
+import 'package:flame/src/events/messages/double_tap_event.dart';
+import 'package:flutter/gestures.dart';
+import 'package:meta/meta.dart';
+
+/// [DoubleTapDispatcher] propagates double-tap events to every components in
+/// the component tree that is mixed with [DoubleTapCallbacks]. This will be
+/// attached to the [FlameGame] instance automatically whenever any
+/// [DoubleTapCallbacks] are mounted into the component tree.
+@internal
+class DoubleTapDispatcher extends Component with HasGameRef<FlameGame> {
+  final _components = <DoubleTapCallbacks>{};
+  bool _eventHandlerRegistered = false;
+
+  void _onDoubleTapDown(DoubleTapDownEvent event) {
+    event.deliverAtPoint(
+      rootComponent: game,
+      eventHandler: (DoubleTapCallbacks component) {
+        _components.add(component..onDoubleTapDown(event));
+      },
+    );
+  }
+
+  void _onDoubleTapUp(DoubleTapEvent event) {
+    _components.forEach((component) => component.onDoubleTapUp(event));
+    _components.clear();
+  }
+
+  void _onDoubleTapCancel(DoubleTapCancelEvent event) {
+    _components.forEach((component) => component.onDoubleTapCancel(event));
+    _components.clear();
+  }
+
+  @override
+  void onMount() {
+    if (game.firstChild<DoubleTapDispatcher>() == null) {
+      game.gestureDetectors.add(
+        DoubleTapGestureRecognizer.new,
+        (DoubleTapGestureRecognizer instance) {
+          instance.onDoubleTapDown =
+              (details) => _onDoubleTapDown(DoubleTapDownEvent(details));
+          instance.onDoubleTapCancel =
+              () => _onDoubleTapCancel(DoubleTapCancelEvent());
+          instance.onDoubleTap = () => _onDoubleTapUp(DoubleTapEvent());
+        },
+      );
+      _eventHandlerRegistered = true;
+    } else {
+      removeFromParent();
+    }
+  }
+
+  @override
+  void onRemove() {
+    if (!_eventHandlerRegistered) {
+      return;
+    }
+
+    game.gestureDetectors.remove<DoubleTapGestureRecognizer>();
+    _eventHandlerRegistered = false;
+  }
+}

packages/flame/lib/src/events/messages/double_tap_cancel_event.dart

@@ -0,0 +1,3 @@
+import 'package:flame/src/events/messages/event.dart';
+
+class DoubleTapCancelEvent extends Event {}

packages/flame/lib/src/events/messages/double_tap_down_event.dart

@@ -0,0 +1,14 @@
+import 'package:flame/extensions.dart';
+import 'package:flame/src/events/messages/position_event.dart';
+import 'package:flutter/gestures.dart';
+
+class DoubleTapDownEvent extends PositionEvent {
+  final PointerDeviceKind deviceKind;
+
+  DoubleTapDownEvent(TapDownDetails details)
+      : deviceKind = details.kind ?? PointerDeviceKind.unknown,
+        super(
+          canvasPosition: details.localPosition.toVector2(),
+          devicePosition: details.globalPosition.toVector2(),
+        );
+}

packages/flame/lib/src/events/messages/double_tap_event.dart

@@ -0,0 +1,3 @@
+import 'package:flame/src/events/messages/event.dart';
+
+class DoubleTapEvent extends Event {}