fix: Ray should not be able to escape CircleHitbox (#3341)

A raycasted ray should not be able to escape a `CircleHitbox` if it
originates from inside of it (or on the edge and has a direction
inwards).
Fixes: #3333

packages/flame/lib/src/collisions/hitboxes/circle_hitbox.dart

@@ -44,10 +44,11 @@ class CircleHitbox extends CircleComponent with ShapeHitbox {
     // the parent size and the radius is defined from the shortest side.
   }
 
-  late final _temporaryLineSegment = LineSegment.zero();
-  late final _temporaryNormal = Vector2.zero();
-  late final _temporaryCenter = Vector2.zero();
-  late final _temporaryAbsoluteCenter = Vector2.zero();
+  static final _temporaryLineSegment = LineSegment.zero();
+  static final _temporaryNormal = Vector2.zero();
+  static final _temporaryCenter = Vector2.zero();
+  static final _temporaryAbsoluteCenter = Vector2.zero();
+  static final _temporaryOrigin = Vector2.zero();
 
   @override
   RaycastResult<ShapeHitbox>? rayIntersection(
@@ -56,6 +57,13 @@ class CircleHitbox extends CircleComponent with ShapeHitbox {
   }) {
     var isInsideHitbox = false;
     _temporaryLineSegment.from.setFrom(ray.origin);
+    // Adding a small value to the origin to avoid the ray to be on the edge
+    // of the circle and then directly intersecting and causing the reflecting
+    // ray to go in the wrong direction.
+    _temporaryOrigin.setValues(
+      ray.origin.x + ray.direction.x * 0.00001,
+      ray.origin.y + ray.direction.y * 0.00001,
+    );
     _temporaryAbsoluteCenter.setFrom(absoluteCenter);
     _temporaryCenter
       ..setFrom(_temporaryAbsoluteCenter)
@@ -73,7 +81,7 @@ class CircleHitbox extends CircleComponent with ShapeHitbox {
         ..y *= (ray.direction.y.sign * _temporaryLineSegment.to.y.sign);
     }
 
-    if (ray.origin.distanceToSquared(_temporaryAbsoluteCenter) <
+    if (_temporaryOrigin.distanceToSquared(_temporaryAbsoluteCenter) <
         radius * radius) {
       _temporaryLineSegment.to.scaleTo(2 * radius);
       isInsideHitbox = true;
@@ -105,7 +113,10 @@ class CircleHitbox extends CircleComponent with ShapeHitbox {
               origin: intersectionPoint,
               direction: reflectionDirection,
             )) ??
-          Ray2(origin: intersectionPoint, direction: reflectionDirection);
+          Ray2(
+            origin: intersectionPoint,
+            direction: reflectionDirection,
+          );
 
       result.setWith(
         hitbox: this,

packages/flame/test/collisions/collision_detection_test.dart

@@ -1804,6 +1804,31 @@ void main() {
         expect(reflectionRay2?.origin, Vector2(50, 0));
         expect(reflectionRay2?.direction, Vector2(1, 1)..normalize());
       },
+      'make sure that ray does not escape circle hitbox': (game) async {
+        final world = (game as FlameGame).world;
+        final circle = CircleComponent(
+          position: Vector2(0, 0),
+          radius: 5,
+          anchor: Anchor.center,
+        )..add(CircleHitbox());
+        await world.ensureAdd(circle);
+        final ray = Ray2(
+          origin: Vector2(0, 0),
+          direction: Vector2(1.0, 0),
+        );
+        final results = game.collisionDetection.raytrace(ray);
+        expect(results.length, 10);
+        expect(results.first.isActive, isTrue);
+        expect(results.first.isInsideHitbox, isTrue);
+        expect(
+          results.first.intersectionPoint,
+          Vector2(5, 0),
+        );
+        final reflectionRay = results.first.reflectionRay;
+        expect(reflectionRay?.origin, Vector2(5, 0));
+        expect(reflectionRay?.direction, Vector2(-1, 0)..normalize());
+        expect(results.first.normal, Vector2(-1, 0));
+      },
     });
   });