unity-physicscore2d-filtering

Implement PhysicsCallbacks.IContactFilterCallback and return false from OnContactFilter2D to suppress a contact. Enable contactFilterCallbacks on the shapes and world, and set the shape's callbackTarget to your MonoBehaviour.

Store identity in PhysicsUserData on the shape, such as an intValue group ID and boolValue participation flag. The callback can read userData from both shapes without touching managed MonoBehaviour state, which keeps it thread-safe.

Yes, OnContactFilter2D can fire off the main thread and in parallel. Only perform read-only access to physics state, avoid writes and allocations, and prefer PhysicsUserData over reflection for identifying shapes.

Contact filtering suppresses contacts during the physics step via IContactFilterCallback. Post-simulate filtering subscribes to PhysicsEvents.PostSimulate and inspects produced contacts with PhysicsShape.GetContacts(), letting you react to contacts matching predicates like normal angle or impulse.

Mark shapes as sensors so they detect overlaps without producing collision response, then handle the overlap events for pickups, goal zones, or damage areas. Keep trigger geometry simple and unregister callbacks when the object is disabled.