Non-hierarchical child-parent transformation

Question

I have two objects, a parent object and a child object, the child object has a list of points that I use with a line renderer to visualize, this points don't follow the parent transforms, they are a list of Vector3. that I asign in run time, think of drawing on a sphere. and I want the drawing to move and rotate along with the spehre. I asign them with a raycast on the spehre.

 for (int i = 0; i < pathPoints.Count; i++)
 {
     Quaternion rotation = transform.parent.transform.rotation;
     Matrix4x4 m = Matrix4x4.TRS(transform.parent.position, rotation, Vector3.one);
     pathPoints[i] = m.GetColumn(3);
 }

This is what I have right now, with this, when I move the spehre (parent) the child object follows normally and the point from the child component follows too but goes to the parent's position. so that's a start, I just need the points to retain their local position and when the parent rotates moving them as if they were regular transform objects parented by hierarchy.

Answer 1

Found an old similar question and now it works the current code I use is this

     Vector3 startPathPosition;
     
         void Start()
         {
             startPathPosition = pathPoints[0];
     
             startPathPosition = DivideVectors(Quaternion.Inverse(transform.parent.rotation) * (startPathPosition - transform.parent.position), Vector3.one);
         }
     
          Vector3 DivideVectors(Vector3 num, Vector3 den) {
      
              return new Vector3(num.x / den.x, num.y / den.y, num.z / den.z);
      
          }
     
         void Update()
         {
             if (pathPoints.Count > 0)
             {
                 for (int i = 0; i < pathPoints.Count; i++)
                 {
                     Quaternion rotation = transform.parent.transform.rotation;
                     Matrix4x4 m = Matrix4x4.TRS(transform.parent.position, rotation, Vector3.one);
     
                     pathPoints[i] = m.MultiplyPoint3x4(startPathPosition);
                 }
             }
        }

it's hard coded to use the first point of the list I was using for reference to place a cube and see what was going on. but it works fine. scale is set to vector3.one as I don't change the scale of the parent object.

Non-hierarchical child-parent transformation

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