Rotate an object on itself, from one random Quaternion to another

Question

I have a situation: I have a 3D object in the world. let's say a sphere. I have 2 random directionnal vector: vector A, and vectorB:

My question is: How to I rotate over time my object, from A to B ? The vector A is important: I don't want to simply rotate the forward of the object from current forward to B.

I know I can use the function vector3 C = Vector3.SmoothDamp(...) in unity to lerp between my 2 vectors A & B.

but then ok, I have vector3 C, how do I apply the rotationof my object to C ? if don't want to do: gameObject.transform.forward = C;

I want something like: gameObject.transform.rotation = SomeQuaternion(C, initial rotation A). or something.

Thank you for help !

PS: I don't want to parent / unparent gameObject or something like that, i want the math answer, using Quaternion.

Answer 1

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New Answer

Since you have two vectors to begin with, instead of two quaternions, Find the quaternion representing the rotation from one vector to another.

Then you can take a copy of the current rotation quaternion, and multiply it with the quaternion you got from the vectors, which gives you the final rotation quaternion. You can then lerp from your copy of the current rotation quaternion to the final rotation quaternion you computed.

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Old Answer

You had the right keyword: lerp.

To be more precise, Quaternion.Lerp.

Example from docs.unity3d.com:

using UnityEngine;

public class Example : MonoBehaviour
{
    // Interpolates rotation between the rotations
    // of from and to.
    // (Choose from and to not to be the same as
    // the object you attach this script to)

    Transform from;
    Transform to;
    float speed = 0.1f;
    void Update()
    {
        transform.rotation = Quaternion.Lerp(from.rotation, to.rotation, Time.time * speed);
    }
}