Calculate new rotation for an object along two axis

Unity Engine
1

I have a cube that I want to rotate. I want to randomly calculate a new rotation for the cube and slerp to the new rotation. I want to be able to rotate it around the y and x axis but I don’t want it to rotate around the z axis.

Here is the code I tried to use for this purpose but it seems to rotate along only the z axis even though my “newRotation” vector3 has a z value that never changes. I’m sure this is just something about Quaternion rotation that I don’t understand, please help! :slight_smile:

private void slowMove()
{
    // if we're in our origin rotation, then pick a new random rotation
    // x +/- 90 degrees, y +/- 90 degrees and z +/- 90 degrees from our
    // current rotation
    float rotationVariance = 90;

    var newRotation = new Vector3(_originalRotation.x + UnityEngine.Random.Range(rotationVariance * -1, rotationVariance), _originalRotation.y + UnityEngine.Random.Range(rotationVariance * -1, rotationVariance), _originalRotation.z);

    _toRotation = Quaternion.FromToRotation(_originalRotation.eulerAngles, newRotation);

    //UnityEngine.Random.rotation;
}

void Update()
{
    if (_toRotation != null)
    {
        // slowly move to our new rotation over time
        transform.rotation = Quaternion.Slerp(transform.rotation, _toRotation.Value, Mathf.Clamp01(Time.deltaTime * 10));

        // until the difference in angle between our current rotation and
        // our destination rotation is < 1
        if (Quaternion.Angle(transform.rotation, _toRotation.Value) < 1)
        {
            _toRotation = null;
        }
    }
}

Here’s an ani gif showing the rotation. Each time it rotates again it’s after I have clicked it.

As you can see it’s only rotating on the z axis for some reason even though the z value should not be changing.

2

Change your _toRotation to a Vector3 and set it to the new rotation vector. Use Vector3.RotateTowards(or Vector3.Slerp) instead of Quaternion.Slerp and then update transform.rotation with Quaternion.Euler.

3

BOOM! That worked, thanks! My final code if anyone is interested.

private void slowMove()
{
    // if we're in our origin rotation, then pick a new random rotation
    // x +/- ? degrees and y +/- ? degrees from our current rotation
    float rotationVariance = 45;

    _toRotation = Quaternion.Euler(_originalRotation.x + UnityEngine.Random.Range(rotationVariance * -1, rotationVariance), _originalRotation.y + UnityEngine.Random.Range(rotationVariance * -1, rotationVariance), _originalRotation.z);
}

void Update()
{
    if (_toRotation != null)
    {
        // slowly move to our new rotation over time
        transform.rotation = Quaternion.Slerp(transform.rotation, _toRotation.Value, Mathf.Clamp01(Time.deltaTime * 10));

        // until the difference in angle between our current rotation and
        // our destination rotation is < 1
        if (Quaternion.Angle(transform.rotation, _toRotation.Value) < 1)
        {
            _toRotation = null;
        }
    }
}
4

I updated my reply with Vector3 methods that might be slightly faster than the Quaternion functions.