using Collider->GetChild returns non-existent entity

[humble quarry]

I'm attempting to find the wheel of a vehicle that's colliding with the ground, but using GetChild on the vehicle collider returns a non existent entity, any suggestions?

struct WheelCollisionJob : ICollisionEventsJob
{
    [ReadOnly] public ComponentLookup<VehicleComponent> vehicleComponentLookup;

    [ReadOnly] public ComponentLookup<PhysicsCollider> physicsColliderLookup;

    [ReadOnly] public ComponentLookup<WheelComponent> wheelComponentLookup;

    public void Execute(CollisionEvent collisionEvent)
    {
        Entity vehicleEntity = GetVehicleEntity(collisionEvent, out ColliderKey vehicleColliderKey);

        if (vehicleEntity == Entity.Null) return;

        Debug.Log("vehicle Entity");

        if (!physicsColliderLookup.TryGetComponent(vehicleEntity, out PhysicsCollider vehiclePhysicsCollider)) return;

        Debug.Log("vehicle physics collider");

        Entity wheelEntity = GetWheelChildCollidedEntity(vehiclePhysicsCollider, ref vehicleColliderKey);
//stops here
        if (wheelEntity == Entity.Null) return;

        Debug.Log("wheel collision");
    }

    Entity GetWheelChildCollidedEntity(PhysicsCollider vehiclePhysicsCollider, ref ColliderKey vehicleColliderKey)
    {
        unsafe
        {
            if (!vehiclePhysicsCollider.ColliderPtr->GetChild(ref vehicleColliderKey, out ChildCollider vehicleEntityChildCollided)) return Entity.Null;

            if (wheelComponentLookup.HasComponent(vehicleEntityChildCollided.Entity)) return vehicleEntityChildCollided.Entity;

            return Entity.Null;
        }
    }

    private Entity GetVehicleEntity(CollisionEvent collisionEvent, out ColliderKey vehicleColliderKey)
    {
        if (vehicleComponentLookup.HasComponent(collisionEvent.EntityA))
        {
            vehicleColliderKey = collisionEvent.ColliderKeyA;
            return collisionEvent.EntityA;
        }
        else if (vehicleComponentLookup.HasComponent(collisionEvent.EntityB))
        {
            vehicleColliderKey = collisionEvent.ColliderKeyB;
            return collisionEvent.EntityB;
        }

        vehicleColliderKey = ColliderKey.Empty;
        return Entity.Null;
    }
}```

[dreamy canopy]

entity with collider doesn't have your component

potentially your wheel is just child entity of your collider entity

inspect subscene in edit mode

and see how your component-entity relationships are setup for your wheels

[humble quarry]

are you referring to the vehicle entity or wheel entity?

[dreamy canopy]

whatever is relevant here

you check collider entity - it has no component

are you sure it's supposed to?

[humble quarry]

just checked my vehicle entity during runtime, the vehicle has a physics collider and vehicle component, and the wheel has a wheel component, but no physics collider? (there are physics colliders in the prefab)

the wheel is 4 stages deep in the hierchy

[dreamy canopy]

physics colliders can only exist at root of physics body

so they probably get moved to root

while your wheel is somehwere as a child

[humble quarry]

so does this mean unity creates a fake entity child?

[dreamy canopy]

no

just inspect your wheel

and find you collider

[humble quarry]

I'm getting entities returned when I do GetChild that don't exist in the inspector though

it's got a collider

[dreamy canopy]

authoring does not match runtime 1 to 1

inspect entities

not game objects

[humble quarry]

wheels have got a wheel component

when I debug cs if (!vehiclePhysicsCollider.ColliderPtr->GetChild(ref vehicleColliderKey, out ChildCollider vehicleEntityChildCollided)) return Entity.Null;
vehicleEntityChildCollided, it prints out an entity that doesn't exist in the inspector, any reason for this?

I was thinking of making use of the keys in the Physics Collider Key Entity Pair buffer (on the root entity), might lead me somewhere

yep, looks like the collider keys in the root entity buffer match the ones in the collision event, will cache those and use them to find the correct entity