Quaternion.rotation and .localRotation behaving identical

Unity Engine
1

I am trying to have one object rotate based on the rotation of a second object, but only when that object is “activated” by a button. (Specifically, have an object rotated when one of the buttons on an HTC Vive controller is pressed.)

In an effort to test the code before worrying about an external controller, I wrote the following with a Boolean as the “button”:

    public GameObject trackedObject;
    public bool buttonPressTest;

    private GameObject go;
    private Transform goT;
    private Transform trackedObjectT;
    private Quaternion trackedObjectQF;
    private Quaternion trackedObjectQT;
   
    // Use this for initialization
    void Start ()
    {
        //Define go as the object the script is attached to and get its Transform
        go = this.gameObject;
        goT = go.GetComponent<Transform>();
        //Get the tracked object's transform
        trackedObjectT = trackedObject.GetComponent<Transform>();

    }
   
    // Update is called once per frame
    void Update ()
    {
       
        if (buttonPressTest == false)
        {
            //Set trackedObjectQF to the current rotation of the tracked object
            trackedObjectQF = trackedObjectT.rotation; 
           
        }
       

        if (buttonPressTest == true)
        {

            trackedObjectQT = trackedObjectT.rotation;
            //Debug.Log(trackedObjectQT);

            Quaternion relative = Quaternion.Inverse(trackedObjectQF) * trackedObjectQT;
            //Debug.Log(relative);

            //Calculate the changes in rotation that has happened after button press and apply them to go
            goT.rotation = relative * goT.rotation; 

            //Update trackedObjectQF to the current rotation of the tracked object
            trackedObjectQF = trackedObjectT.rotation;
            //Debug.Log(trackedObjectQF);


        }

    }

However, all of the rotations are behaving as if they are local, not global. For example, a rotation about an object’s local x-axis rotates the second object about its x-axis, instead of the rotations taking place about a global axis. Any suggestion for how to make the rotations correspond to global axes?

2

Transform.localRotation uses the object’s parent Transform’s axes for the rotation. I think what you want is to use Transform.Rotate() using the Space.World value for the relativeTo argument.

3

Transform.Rotate() requires a Vector3, doesn’t it? I am hoping that this can be done with converting Quaternions into Vector3s, etc.

4

you should also cache the GoT rotation when press is false, and you’re calculating Relative and the goT.rotation backwards.

        if (buttonPressTest == false)
        {
            //Set trackedObjectQF to the current rotation of the tracked object
            trackedObjectQF = trackedObjectT.rotation;
            goTQF = goT.rotation;
        }
     
        if (buttonPressTest == true)
        {
            trackedObjectQT = trackedObjectT.rotation;

            Quaternion relative = trackedObjectQT * Quaternion.Inverse(trackedObjectQF);

            //Calculate the changes in rotation that has happened after button press and apply them to go
            goT.rotation = goTQF * relative;
        }

recalculating from the cached rotation every frame will prevent accumulation of floating precision loss.
instead of inverse(fromRotation) * currentRotation, use currentRotation * Inverse(FromRotation) which will give you the difference of (current - from), aka the delta rotation.
finally. goTFromRotation * relative (aka starting rotation * delta rotation) will give you the offset that goT needs to be rotated to as its updated.

5

Thanks for the suggestions! Unfortunately, the behavior remains the same. Rotations are synched using the local axis instead of the global axis.