Raycast misses object untill I manually disable and re-enable box collider on it

Hello all,

I am working on serialization/deserialization system which includes storing RigidBody state in Google Protobuf-based structures. The deserialization step is done in Awake() function inside script accessible on given scene - where the previous content of scene is Destroy'ed and new one is loaded.

Recently I got a very stange bug that is reproducable (sadly, not always) on complex scenes, but it slips away when trying to minimize code involved.

Basically the situation is that after loading a scene sometimes raycast misses the object clearly in position:



When I manually disable and re-enable box collider on this object:



The raycast starts to hits OK (from the next frame):



It is obvious that I miss a step to re-generate Physics state after de-serialization, but sadly I don't know which.

I tried:
- Calling `Physics.SyncTransforms` after load - no effect
- Moving object manually without reenabling collider -> raycast would still miss them
- Calling `Rigidbody.ResetInertiaTensor` after load on the box - no effect

Raycasts in question are cast every frame in Update and they miss every time until I manually disable and then re-enable collision. The problem does not manifest always, leading me to believe there is some kind of race condition...

I tried also work-arounding:

Code (CSharp):

1. foreach(var collider in FindObjectsOfType<Collider>(false))
2. {
3.        collider.enabled = false;
4.        collider.enabled = true;
5. }

But had no effect on raycast as well.

To specify: the 'normal' collisions between objects are working, only raycasts are failing (and only till I disable and re-enable colliders)...

 

Unity version: 2021.1.12f1

 

Dear shelim,

I have a similar problem.
After loading a scene additively, the raycasts will work only after re-enabling colliders, and only for about 2 seconds.

Did you find a solution?
I am currently on Unity 2020.3.4f1

 

Actually I had!

After careful examination and pinpointing the problem I found out that calling DestroyImmediate on any physics-based gameObject is broken and will broke other physics-related things, even happening much later on (including random crashes in final build!).

I ended up with deserialization step split into several frames - first, I delete all existsing objects (via normal Destroy), wait a fixed frame until physics get to know the objects are not longer there, then re-create serialized gameObjects

 

Hi shelim,
hi MelvMay

thank you for the rapid response!
It did not help me yet, but this rabbithole seems rather deep.

 

Yes, I understand that clearly; I was under false impression I am solving a different bug altogether, having an rigidbody destroyed, then spawned another rigidbody in similiar position, with inertia/speed/etc. loaded from serialized data would still result in physics to consider both objects overlapping for the duration of the frame. This resulted in all loaded stuff that overlapped with destroyed stuff to bump up on the instant of load. As I said, the only solution I found was to spread loading to separate frames (ie. there is nothing which could tell physics to remove instantly object from simulation)

 

After more testing I found out that the problem will only manifest if called from FixedUpdate.

Relevant code:

Code (CSharp):

1.  
2. public class Respawn : MonoBehaviour
3. {
4.     public Rigidbody PrevObject;
5.     public Rigidbody NextObject;
6.  
7.     public Text TextInfo;
8.  
9.     private bool isLoading;
10.  
11.     private void Update()
12.     {
13.         if (Input.GetKeyDown(KeyCode.Space))
14.             isLoading = true;
15.     }
16.  
17.     void FixedUpdate()
18.     {
19.         if (isLoading)
20.         {
21.             isLoading = false;
22.  
23.             var pos = PrevObject.transform.position;
24.             var rot = PrevObject.transform.rotation;
25.             Destroy(PrevObject.gameObject);
26.             PrevObject = Instantiate(NextObject, Vector3.zero, Quaternion.identity);
27.             PrevObject.transform.position = pos;
28.             PrevObject.transform.rotation = rot;
29.             PrevObject.velocity = Vector3.zero;
30.             PrevObject.angularDrag = 0;
31.             PrevObject.angularVelocity = Vector3.zero;
32.             TextInfo.text = "Removed a box and created new one!";
33.         }
34.     }
35. }
36.  

See recording:


Repro scene attached

 

The new position was comming from serialization system, but just to be 100% sure I changed the relevant line to (and removed manually setting pos/rot later on):

Code (CSharp):

1. PrevObject = Instantiate(NextObject, pos, rot);

The bumping up effect is still happening.

 

Transform, I copied them into Vector/Quaternion structs then destroyed original object. But copying from RigidBody yields in the same values...

I was doing that experiments when I originally encountered the problem It made no difference, and that was why I was under false impression of DestroyImmediate is required in this case.

To clarify: I was attempting to reset all RigidBody properties from serialized data, including impulse. I also tried to spawning object in the next frame by yielding, and this indeed solved the problem.