fix: PropagatingCollisionBehavior should also work for non entity c…

…omponents (#20)

* bug: `PropagatingCollisionBehavior` should also work for non entity components

* bug: `PropagatingCollisionBehavior` should also work for non entity components

example/lib/behaviors/behaviors.dart

@@ -1,2 +1,3 @@
 export 'movement_behavior.dart';
 export 'rotation_behavior.dart';
+export 'screen_collision_behavior.dart';

example/lib/behaviors/rotation_behavior.dart

@@ -19,14 +19,5 @@ class RotationBehavior extends Behavior with HasGameRef {
   void update(double dt) {
     final angleDelta = dt * rotationSpeed;
     parent.angle = (parent.angle + angleDelta) % (2 * pi);
-    // Takes rotation into consideration (which topLeftPosition doesn't)
-    final topLeft = parent.absoluteCenter - (parent.scaledSize / 2);
-    if (topLeft.x + parent.scaledSize.x < 0 ||
-        topLeft.y + parent.scaledSize.y < 0 ||
-        topLeft.x > screenHitbox.scaledSize.x ||
-        topLeft.y > screenHitbox.scaledSize.y) {
-      final moduloSize = screenHitbox.scaledSize + parent.scaledSize;
-      parent.topLeftPosition = parent.topLeftPosition % moduloSize;
-    }
   }
 }

example/lib/behaviors/screen_collision_behavior.dart

@@ -0,0 +1,21 @@
+import 'package:flame/collisions.dart';
+import 'package:flame_behaviors/flame_behaviors.dart';
+
+/// Simplified "screen wrapping" behavior, while not perfect it does showcase
+/// the possibility of acting on collision with non-entities.
+class ScreenCollisionBehavior extends CollisionBehavior<ScreenHitbox, Entity> {
+  @override
+  void onCollisionEnd(ScreenHitbox other) {
+    if (parent.position.x < other.position.x) {
+      parent.position.x = other.position.x + other.scaledSize.x;
+    } else if (parent.position.x > other.position.x + other.scaledSize.x) {
+      parent.position.x = other.position.x;
+    }
+
+    if (parent.position.y < other.position.y) {
+      parent.position.y = other.position.y + other.scaledSize.y;
+    } else if (parent.position.y > other.position.y + other.scaledSize.y) {
+      parent.position.y = other.position.y;
+    }
+  }
+}

example/lib/entities/circle/circle.dart

@@ -19,6 +19,7 @@ class Circle extends Entity with HasPaint {
             PropagatingCollisionBehavior(CircleHitbox()),
             CircleCollisionBehavior(),
             RectangleCollisionBehavior(),
+            ScreenCollisionBehavior(),
             MovementBehavior(velocity: velocity),
             RotationBehavior(rotationSpeed: rotationSpeed),
             DraggingBehavior()

example/lib/entities/rectangle/rectangle.dart

@@ -17,6 +17,7 @@ class Rectangle extends Entity with HasPaint {
             PropagatingCollisionBehavior(RectangleHitbox()),
             RectangleCollisionBehavior(),
             CircleCollisionBehavior(),
+            ScreenCollisionBehavior(),
             MovementBehavior(velocity: velocity),
             RotationBehavior(rotationSpeed: rotationSpeed),
             FreezeBehavior(),

example/lib/main.dart

@@ -14,7 +14,7 @@ class ExampleGame extends FlameGame
     await add(ScreenHitbox());
 
     var shapeEntity = _randomEntity(
-      position: Vector2.zero(),
+      position: size / 2,
       size: Vector2.all(50) + Vector2.random(_rng) * 100,
     );
     await add(shapeEntity);
@@ -26,17 +26,10 @@ class ExampleGame extends FlameGame
   }
 
   final _rng = Random();
-  final _distance = Vector2(100, 0);
 
   Entity nextRandomEntity(Entity entity) {
     final size = Vector2.all(50) + Vector2.random(_rng) * 100;
-    final isXOverflow =
-        entity.position.x + entity.size.x / 2 + _distance.x + size.x > size.x;
-    var position = _distance + Vector2(0, entity.position.y + 200);
-    if (!isXOverflow) {
-      position = (entity.position + _distance)..x += size.x / 2;
-    }
-    return _randomEntity(position: position, size: size);
+    return _randomEntity(position: this.size / 2, size: size);
   }
 
   Entity _randomEntity({

lib/src/behaviors/propagating_collision_behavior.dart

@@ -26,9 +26,8 @@ abstract class CollisionBehavior<Collider extends Component,
   bool get isColliding {
     final propagatingCollisionBehavior =
         parent.findBehavior<PropagatingCollisionBehavior>();
-    final activeCollisions = propagatingCollisionBehavior.activeCollisions;
 
-    return activeCollisions
+    return propagatingCollisionBehavior.activeCollisions
         .map(propagatingCollisionBehavior._findEntity)
         .whereType<Collider>()
         .isNotEmpty;
@@ -54,9 +53,9 @@ abstract class CollisionBehavior<Collider extends Component,
 /// Any other entity that has a [CollisionBehavior] for that entity attached
 /// will then be able to collide with it.
 ///
-/// **Note**: This behavior can only be used for collisions between entities.
-/// It cannot be used for collisions between an entity and a non-entity
-/// component.
+/// **Note**: This behavior can also be used for collisions between entities
+/// and non-entity components, by passing the component's type as the
+/// `Collider` to the [CollisionBehavior].
 /// {@endtemplate}
 class PropagatingCollisionBehavior extends Behavior with CollisionCallbacks {
   /// {@macro propagating_collision_behavior}
@@ -77,10 +76,17 @@ class PropagatingCollisionBehavior extends Behavior with CollisionCallbacks {
   /// List of [CollisionBehavior]s to which it can propagate to.
   List<CollisionBehavior> _propagateToBehaviors = [];
 
-  Entity? _findEntity(PositionComponent other) {
+  /// Tries to find the entity that is colliding with the given entity.
+  ///
+  /// It will check if the parent is either a [PropagatingCollisionBehavior]
+  /// or a [Entity]. If it is neither, it will return [other].
+  Component? _findEntity(PositionComponent other) {
     final parent = other.parent;
     if (parent is! PropagatingCollisionBehavior && parent is! Entity) {
-      return null;
+      if (other is ShapeHitbox) {
+        return other.parent;
+      }
+      return other;
     }
 
     return parent is Entity
@@ -96,7 +102,7 @@ class PropagatingCollisionBehavior extends Behavior with CollisionCallbacks {
     activeCollisions.add(other);
     final otherEntity = _findEntity(other);
     if (otherEntity == null) {
-      return super.onCollisionStart(intersectionPoints, other);
+      return;
     }
 
     for (final behavior in _propagateToBehaviors) {
@@ -112,7 +118,7 @@ class PropagatingCollisionBehavior extends Behavior with CollisionCallbacks {
   void onCollision(Set<Vector2> intersectionPoints, PositionComponent other) {
     final otherEntity = _findEntity(other);
     if (otherEntity == null) {
-      return super.onCollision(intersectionPoints, other);
+      return;
     }
 
     for (final behavior in _propagateToBehaviors) {
@@ -128,7 +134,7 @@ class PropagatingCollisionBehavior extends Behavior with CollisionCallbacks {
     activeCollisions.remove(other);
     final otherEntity = _findEntity(other);
     if (otherEntity == null) {
-      return super.onCollisionEnd(other);
+      return;
     }
 
     for (final behavior in _propagateToBehaviors) {

test/src/behaviors/propagating_collision_behavior_test.dart

@@ -21,12 +21,10 @@ class _EntityB extends Entity {
 }
 
 class _EntityC extends Entity {
-  _EntityC({
-    super.children,
-  }) : super(size: Vector2.all(16));
+  _EntityC() : super(size: Vector2.all(16));
 }
 
-abstract class _CollisionBehavior<A extends Entity, B extends Entity>
+abstract class _CollisionBehavior<A extends Component, B extends Entity>
     extends CollisionBehavior<A, B> {
   bool onCollisionStartCalled = false;
   bool onCollisionCalled = false;
@@ -55,6 +53,9 @@ class _CollisionBehaviorAtoB extends _CollisionBehavior<_EntityB, _EntityA> {}
 
 class _CollisionBehaviorAtoC extends _CollisionBehavior<_EntityC, _EntityA> {}
 
+class _CollisionBehaviorAtoComponent
+    extends _CollisionBehavior<PositionComponent, _EntityA> {}
+
 void main() {
   final flameTester = FlameTester(TestGame.new);
 
@@ -134,25 +135,37 @@ void main() {
         (game) async {
           final collisionBehaviorAtoB = _CollisionBehaviorAtoB();
           final collisionBehaviorAtoC = _CollisionBehaviorAtoC();
+          final collisionBehaviorAtoComponent =
+              _CollisionBehaviorAtoComponent();
           final entityA = _EntityA(
             behaviors: [
               PropagatingCollisionBehavior(RectangleHitbox()),
               collisionBehaviorAtoB,
-              collisionBehaviorAtoC
+              collisionBehaviorAtoC,
+              collisionBehaviorAtoComponent,
             ],
           );
 
           final entityB = _EntityB(
             behaviors: [PropagatingCollisionBehavior(RectangleHitbox())],
           );
 
+          final positionComponent = PositionComponent(
+            size: Vector2.all(16),
+            children: [
+              RectangleHitbox(),
+            ],
+          );
+
           await game.ensureAdd(entityA);
           await game.ensureAdd(entityB);
+          await game.ensureAdd(positionComponent);
 
           game.update(0);
 
           expect(collisionBehaviorAtoB.onCollisionStartCalled, isTrue);
           expect(collisionBehaviorAtoC.onCollisionStartCalled, isFalse);
+          expect(collisionBehaviorAtoComponent.onCollisionStartCalled, isTrue);
         },
       );
 
@@ -184,86 +197,22 @@ void main() {
         'on end to the correct collision behavior',
         (game) async {
           final collisionBehaviorAtoB = _CollisionBehaviorAtoB();
+          final collisionBehaviorAtoC = _CollisionBehaviorAtoC();
+          final collisionBehaviorAtoComponent =
+              _CollisionBehaviorAtoComponent();
           final entityA = _EntityA(
             behaviors: [
               PropagatingCollisionBehavior(RectangleHitbox()),
               collisionBehaviorAtoB,
+              collisionBehaviorAtoC,
+              collisionBehaviorAtoComponent,
             ],
           );
 
           final entityB = _EntityB(
             behaviors: [PropagatingCollisionBehavior(RectangleHitbox())],
           );
 
-          await game.ensureAdd(entityA);
-          await game.ensureAdd(entityB);
-
-          game.update(0);
-
-          expect(collisionBehaviorAtoB.onCollisionEndCalled, isFalse);
-
-          entityB.position += Vector2.all(50);
-
-          game.update(0);
-
-          expect(collisionBehaviorAtoB.onCollisionEndCalled, isTrue);
-        },
-      );
-
-      group('only if it collides with an entity', () {
-        flameTester.test('on start', (game) async {
-          final collisionBehaviorAtoB = _CollisionBehaviorAtoB();
-          final collisionBehaviorAtoC = _CollisionBehaviorAtoC();
-          final entityA = _EntityA(
-            behaviors: [
-              PropagatingCollisionBehavior(RectangleHitbox()),
-              collisionBehaviorAtoB,
-              collisionBehaviorAtoC
-            ],
-          );
-
-          await game.ensureAdd(entityA);
-          await game.ensureAdd(
-            PositionComponent(
-              size: Vector2.all(16),
-              children: [
-                RectangleHitbox(),
-              ],
-            ),
-          );
-          await game.ensureAdd(
-            _EntityC(
-              children: [
-                RectangleHitbox(),
-              ],
-            ),
-          );
-
-          game.update(0);
-
-          expect(collisionBehaviorAtoB.onCollisionStartCalled, isFalse);
-          expect(collisionBehaviorAtoC.onCollisionStartCalled, isTrue);
-
-          expect(collisionBehaviorAtoB.onCollisionCalled, isFalse);
-          expect(collisionBehaviorAtoC.onCollisionCalled, isTrue);
-        });
-        flameTester.test('on end', (game) async {
-          final collisionBehaviorAtoB = _CollisionBehaviorAtoB();
-          final collisionBehaviorAtoC = _CollisionBehaviorAtoC();
-          final entityA = _EntityA(
-            behaviors: [
-              PropagatingCollisionBehavior(RectangleHitbox()),
-              collisionBehaviorAtoB,
-              collisionBehaviorAtoC
-            ],
-          );
-
-          final entityC = _EntityC(
-            children: [
-              RectangleHitbox(),
-            ],
-          );
-
           final positionComponent = PositionComponent(
             size: Vector2.all(16),
             children: [
@@ -272,20 +221,25 @@ void main() {
           );
 
           await game.ensureAdd(entityA);
+          await game.ensureAdd(entityB);
           await game.ensureAdd(positionComponent);
-          await game.ensureAdd(entityC);
 
           game.update(0);
 
-          entityC.position += Vector2.all(50);
+          expect(collisionBehaviorAtoB.onCollisionEndCalled, isFalse);
+          expect(collisionBehaviorAtoC.onCollisionEndCalled, isFalse);
+          expect(collisionBehaviorAtoComponent.onCollisionEndCalled, isFalse);
+
+          entityB.position += Vector2.all(50);
           positionComponent.position += Vector2.all(50);
 
           game.update(0);
 
-          expect(collisionBehaviorAtoB.onCollisionEndCalled, isFalse);
-          expect(collisionBehaviorAtoC.onCollisionEndCalled, isTrue);
-        });
-      });
+          expect(collisionBehaviorAtoB.onCollisionEndCalled, isTrue);
+          expect(collisionBehaviorAtoC.onCollisionEndCalled, isFalse);
+          expect(collisionBehaviorAtoComponent.onCollisionEndCalled, isTrue);
+        },
+      );
     });
   });
 }