RotateAround an object with using Quaternion

Question

I have a great question for code masters. Think about you have only a calculated rotation value to rotate the transform. But you have to rotate around with its child pivot position. How do you solve this problem?

Thank you for your time :)

Answer 1

Why reinvent the wheel? ;)

Unity has Transform.RotateAround and for the input you could simply use Quaternion.ToAngleAxis like e.g.

public static class TransformExtensions
{
    public static void RotateAround(this Transform transform, Transform pivot, Quaternion rotation)
    {  
        RotateAround (transform, pivot.transform.position, rotation);
    } 

    public static void RotateAround(this Transform transform, Vector3 pivotPoint, Quaternion rotation)
    {   
        rotation.ToAngleAxis(out var angle, out var axis);

        transform.RotateAround(pivotPoint, axis, angle);
    }
}

Answer 2

I wrote the code. Here is the solution.