Any reason why OnControllerColliderHit has a NaN normal?

Questions & Answers
1

I have a small MonoBehaviour script I attach to a game object in the editor, and the game object also has a CharacterController component attached to it. My question is, in my game, I (rarely) get into a situation where the ControllerColliderHit object passed to my OnControllerColliderHit function has a normal with NaN values. Can anybody think of a reason why this would happen? The rest of my source is pretty lengthy so I won’t ask anybody to dig through it, but I use both Move() and transform.position to move the object around.

Here’s the small component I use:

using UnityEngine;
public delegate void CollisionEventHandler(ControllerColliderHit hit);
public class CollisionDetector : MonoBehaviour {
  public CollisionEventHandler OnCollision;
  public void OnControllerColliderHit(ControllerColliderHit hit)
  {
    if (float.IsNaN(hit.normal.x))
      Debug.Log("Collision detector NaN normal");
    if (OnCollision != null)
      OnCollision(hit);
  }
}
2

I have used OnControllerColliderHit a lot, and never observed this issue. Maybe the transform.position changes are fooling the collision system and producing this error - a Character Controller is supposed to be moved only with Move and SimpleMove.

You could try to replace any transform.position assignment like this:

  transform.position = newPosition;

by a Move equivalent:

  character.Move(newPosition-transform.position);

You could also try to do all Move or transform changes in FixedUpdate (the CharacterController belongs to the physics engine like the rigidbodies).

3

I’m in an extremely similar situation and started getting this in Unity 4.3, leading to hard crashes / lockups. It took me literally days to diagnose, all I knew was that my state data was getting corrupted, and I poured through and logged every piece of physics related floating point math in my codebase, thinking I must have played a bit fast and loose somewhere and forgot that floats aren’t reals, or that maybe there was a corner case networking bug, but lo and behold, I find the occasional though incredibly rare NaN filled normal in ControllerColliderHitS.

Why having NaN values in a CC Move would cause a hard crash is beyond me (it should certainly fail more gracefully than that), but a hit normal should quite obviously NEVER NEVER NEVER NEVER NEVER come back NaN. That’s simply not valid and breaks the contract of the API.

For now I guess the solution is to assume Unity physics are even more broken than usual and manually guard against NaN normals.