fix: Destroy and create bodies after step is done (#106)

spydon · web-flow · commit 92c7ccb85774 · 2025-09-07T19:16:20.000+02:00
# Description This creates and destroys bodies after `stepDt` is done to avoid concurrency issues from destroying bodies based on for example taps or other gestures that can happen meanwhile `stepDt` is running. Fixes: flame-engine/flame#3712 ## Checklist  - [x] The title of my PR starts with a [Conventional Commit] prefix (`fix:`, `feat:`, `docs:` etc). - [x] I have read the [Contributor Guide] and followed the process outlined for submitting PRs. - [ ] I have updated/added tests for ALL new/updated/fixed functionality. - [x] I have updated/added relevant documentation in `docs` and added dartdoc comments with `///`. - [x] I have updated/added relevant examples in `examples`. ## Breaking Change  - [ ] Yes, this is a breaking change. - [x] No, this is *not* a breaking change. ## Related Issues   [issue database]: https://github.com/flame-engine/flame/issues [Contributor Guide]: https://github.com/flame-engine/flame/blob/main/CONTRIBUTING.md [Flame Style Guide]: https://github.com/flame-engine/flame/blob/main/STYLEGUIDE.md [Conventional Commit]: https://conventionalcommits.org
diff --git a/packages/forge2d/lib/src/collision/broadphase/dynamic_tree.dart b/packages/forge2d/lib/src/collision/broadphase/dynamic_tree.dart
@@ -461,7 +461,7 @@ class DynamicTree implements BroadPhaseStrategy {
 
   /// returns a node to the pool
   void _freeNode(DynamicTreeNode node) {
-    assert(0 < _nodeCount);
+    assert(_nodeCount > 0);
     node.parent = _freeList != nullNode ? _nodes[_freeList] : null;
     node.height = -1;
     _freeList = node.id;
diff --git a/packages/forge2d/lib/src/dynamics/contact_manager.dart b/packages/forge2d/lib/src/dynamics/contact_manager.dart
@@ -6,12 +6,11 @@ class ContactManager implements PairCallback {
   final Collision collision;
   final Distance distance;
   final List<Contact> contacts = [];
-  ContactFilter? contactFilter;
+  ContactFilter contactFilter;
   ContactListener? contactListener;
 
-  ContactManager(this.broadPhase, this.collision, this.distance) {
-    contactFilter = ContactFilter();
-  }
+  ContactManager(this.broadPhase, this.collision, this.distance)
+    : contactFilter = ContactFilter();
 
   /// Broad-phase callback.
   @override
@@ -49,7 +48,7 @@ class ContactManager implements PairCallback {
     }
 
     // Check user filtering.
-    if (contactFilter?.shouldCollide(fixtureA, fixtureB) == false) {
+    if (contactFilter.shouldCollide(fixtureA, fixtureB) == false) {
       return;
     }
 
@@ -122,7 +121,7 @@ class ContactManager implements PairCallback {
         }
 
         // Check user filtering.
-        if (contactFilter?.shouldCollide(fixtureA, fixtureB) == false) {
+        if (contactFilter.shouldCollide(fixtureA, fixtureB) == false) {
           contactRemovals.add(c);
           continue;
         }
diff --git a/packages/forge2d/lib/src/dynamics/world.dart b/packages/forge2d/lib/src/dynamics/world.dart
@@ -25,6 +25,10 @@ class World {
   late ContactManager contactManager;
   final List<Body> bodies = <Body>[];
   final List<Joint> joints = <Joint>[];
+  final List<Body> bodiesToCreate = <Body>[];
+  final List<Body> bodiesToDestroy = <Body>[];
+  final List<Joint> jointsToCreate = <Joint>[];
+  final List<Joint> jointsToDestroy = <Joint>[];
 
   final Vector2 _gravity;
 
@@ -37,7 +41,7 @@ class World {
   ///
   /// See also:
   ///
-  /// * [Body.gravityScale], to multipy [gravity] for a [Body].
+  /// * [Body.gravityScale], to multiply [gravity] for a [Body].
   /// * [Body.gravityOverride], to change how the world treats the gravity for
   /// a [Body].
   /// {@endtemplate}
@@ -133,8 +137,11 @@ class World {
   ///
   /// Warning: This function is locked during callbacks.
   Body createBody(BodyDef def) {
-    assert(!isLocked);
     final body = Body(def, this);
+    if (isLocked) {
+      bodiesToCreate.add(body);
+      return body;
+    }
     bodies.add(body);
     return body;
   }
@@ -145,8 +152,10 @@ class World {
   /// Warning: This automatically deletes all associated shapes and joints.
   /// Warning: This function is locked during callbacks.
   void destroyBody(Body body) {
-    assert(bodies.isNotEmpty);
-    assert(!isLocked);
+    if (isLocked) {
+      bodiesToDestroy.add(body);
+      return;
+    }
 
     // Delete the attached joints.
     while (body.joints.isNotEmpty) {
@@ -173,10 +182,11 @@ class World {
   /// This may cause the connected bodies to cease colliding.
   ///
   /// Adding a joint doesn't wake up the bodies.
-  ///
-  /// Warning: This function is locked during callbacks.
   void createJoint(Joint joint) {
-    assert(!isLocked);
+    if (isLocked) {
+      jointsToCreate.add(joint);
+      return;
+    }
     joints.add(joint);
 
     final bodyA = joint.bodyA;
@@ -197,10 +207,11 @@ class World {
   }
 
   /// Destroys a joint. This may cause the connected bodies to begin colliding.
-  ///
-  /// Warning: This function is locked during callbacks.
   void destroyJoint(Joint joint) {
-    assert(!isLocked);
+    if (isLocked) {
+      jointsToDestroy.add(joint);
+      return;
+    }
 
     final collideConnected = joint.collideConnected;
     joints.remove(joint);
@@ -297,6 +308,16 @@ class World {
 
     flags &= ~locked;
 
+    for (final body in bodiesToCreate) {
+      bodies.add(body);
+    }
+    bodiesToCreate.clear();
+
+    for (final body in bodiesToDestroy) {
+      destroyBody(body);
+    }
+    bodiesToDestroy.clear();
+
     _profile.step.record(_stepTimer.getMilliseconds());
   }
 
diff --git a/packages/forge2d/pubspec.yaml b/packages/forge2d/pubspec.yaml
@@ -8,7 +8,7 @@ environment:
   sdk: ">=3.8.0 <4.0.0"
 
 dependencies:
-  meta: ^1.17.0
+  meta: ^1.16.0
   vector_math: ^2.2.0
   web: ^1.1.1
 
