Changing a GameObject's tag before adding a fixed joint resets PhysX collision info.

Unity Engine
1

Hi,

I’ve stumbled upon a weird behaviour and wanted to know if this was normal or not.

I start with two rigidbodies (cubes) that are colliding together. I change the tag of the GameObject containing one of the colliding rigidbodies. Then I add a joint to which I attach the other rigidbody whose tag has no been changed. At that point I get an onCollision exit call from the connected body and no more onCollisionStay calls event if the rigidbodies are still touching each other. Here’s my code:

// This is called when both rigidbodies are colliding with each other.
public void JoinBodies(float jointBreakForce, GameObject otherObject)
{
       // Remove this line and OnCollisionExit will not get called
       otherObject.tag = "Grabbed";

	m_joint = otherObject.AddComponent<FixedJoint> ();
	m_joint.connectedBody = this.rigidbody;
	m_joint.breakForce = jointBreakForce;

        // Displaying the object's name just to make sure which one it is
        Debug.Log(otherObject.name);
}

// This is called even if the rigidbodies are still touching each other.
public void OnCollisionExit(Collision c)
{
      Debug.Log(c.gameObject.name);
}

If I do not change the gameObject’s tag OnCollisionExit is not called. Is this a bug? The profiler did not show any spikes in physics when the tag was changed.

2

Is anyone besides me having this problem and thinks PhysX should be updated?