Make contacts deterministic across Worlds #480
Merged
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Objective
We noticed an issue where the Collisions were using the order of
Entity
directly to sort the pair of entities in a contact.The issue is that for networking, there is no guarantee that the pair of Entities that are replicated between a Client and a Server world are in the same direction.
Solution
aabb.min.x
to order the two entities.previous_contacts
here: https://github.com/cBournhonesque/avian/blob/ac1fd0269e04f19f6892c62019cbb9ad9c19444e/src/collision/narrow_phase.rs#L549 because we check both directionsmatch_manifolds
here: https://github.com/cBournhonesque/avian/blob/ac1fd0269e04f19f6892c62019cbb9ad9c19444e/src/collision/narrow_phase.rs#L571 which is why we modify the functionCollisionStarted
andCollisionEnded
events are sent, even if the entities change their order during a contact. we should probably add a test for thisContacts
struct that is generated during the narrow phase, and we made sure that contact matching still works independently of past entity orderTest
aabb.min.x
of the two entities gets swapped during the contact