Problem with Quaternion.LookRotation()

Questions & Answers
1

I’ve written a function that’s supposed to make a GameObject face another GameObject, and return the resulting Quaternion if I only want to use part of it.

The problem I’m having with it is that if the object is facing away from the target the first time I call the function on it, it faces away from the target rather than towards it (= the rotation is inverted by 180 degrees). If the object is already rotated in the target’s general direction, the rotation works fine.

Here’s the source for the function I’m using:

    Quaternion LookAt2D(GameObject tracker, GameObject target)
    {
        Vector3 trackerPosition = new Vector3(
            tracker.transform.position.x,
            tracker.transform.position.y,
            0.0f);

        Vector3 targetPosition = new Vector3(
            target.transform.position.x,
            target.transform.position.y,
            0.0f);

        Quaternion rotation = Quaternion.LookRotation
            (targetPosition - trackerPosition, tracker.transform.TransformDirection(Vector3.up));
        tracker.transform.rotation = new Quaternion(0, 0, rotation.z, rotation.w);

        return rotation;
    }

Here’s the problem in action.

Before starting the scene:
alt text

After starting the scene:
alt text

Both of the turrets are the exact same GameObject, with the exact same script attached.

2

Hah, alright, it looks like I sort of solved my own problem. I just added this code to the beginning of the function, making the object face the target before calculating the rotation.

        if (tracker.transform.position.x > target.transform.position.x)
        {
            tracker.transform.eulerAngles = new Vector3(0, 0, 360);
        }
        else
        {
            tracker.transform.eulerAngles = new Vector3(0, 0, 180);
        }

I would really like to know why this happens, though. Is it a Unity bug or just a matter of me not understanding Quaternions?