Question Probuilder flatten terrain over time

Hello there,

I'm trying to make some kind of animation for flattening the terrain over some x period of time.
But unfortunately, my terrain flattens almost at a constant speed regardless of the time it should take.

So pretty much no matter what duration I set it flattens really quick and I have to wait for the Debug.log to fire rest of the time. Whereas I would like it to flatten at the speed of duration so it really takes some x seconds before it's flattened

My code:

Code (CSharp):

1. IEnumerator FlattenTerrain(float duration) {
2.     float time = 0;
3.     Vertex[] vertices = m_Mesh.GetVertices();
4.  
5.    // lerp vertices to 0 over time
6.     while (time < duration) {
7.       foreach (Vertex vertex in vertices) {
8.         if (vertex.position.y <= Mathf.Epsilon)
9.           continue;
10.  
11.         Vector3 newPosition = vertex.position;
12.         newPosition.y = Mathf.Lerp(vertex.position.y, 0, time / duration);
13.  
14.         vertex.position = newPosition;
15.       }
16.  
17.       time += Time.deltaTime;
18.  
19.       m_Mesh.SetVertices(vertices);
20.       m_Mesh.ToMesh();
21.       m_Mesh.Refresh();
22.  
23.       yield return null;
24.     }
25.  
26.   // set vertices exactly to 0 because of overshoot
27.     Vertex[] flattenedVertices = m_Mesh.GetVertices()
28.      .Select(
29.         vertex => {
30.           Vector3 pos = vertex.position;
31.           vertex.position = new Vector3(pos.x, 0, pos.z);
32.  
33.           return vertex;
34.         }
35.       )
36.      .ToArray();
37.  
38.     m_Mesh.SetVertices(flattenedVertices);
39.     m_Mesh.ToMesh();
40.     m_Mesh.Refresh();
41.  
42.     MeshUtility.CollapseSharedVertices(m_Mesh.GetComponent<MeshFilter>().sharedMesh);
43.     Debug.Log("VAR");
44.   }

Attached gif -> 2 seconds duration and terrain flattens crazy fast instead over time

 

I got something better but still I don't know how to incorporate Time into the flattening. Now I can flatten at some speed but can't figure out how to add time variable here so It would really take some X time to flatten..

Code (CSharp):

1.   private IEnumerator FlattenTerrain(float flattenSpeed) {
2.     float time = 0;
3.     float verticesLeft = float.MaxValue;
4.  
5.     Vertex[] vertices = m_Mesh.GetVertices();
6.  
7.     while (verticesLeft >= Mathf.Epsilon) {
8.       foreach (Vertex vertex in vertices) {
9.         if (vertex.position.y <= Mathf.Epsilon)
10.           continue;
11.  
12.         Vector3 startPos = vertex.position;
13.         Vector3 endPos = new Vector3(startPos.x, 0, startPos.z);
14.  
15.         float distCovered = time * flattenSpeed;
16.         float fractionOfJourney = distCovered / Vector3.Distance(startPos, endPos);
17.  
18.         vertex.position = Vector3.Lerp(startPos, endPos, fractionOfJourney);
19.       }
20.  
21.       time += Time.deltaTime;
22.  
23.       m_Mesh.SetVertices(vertices);
24.       m_Mesh.ToMesh();
25.       m_Mesh.Refresh();
26.  
27.       yield return null;
28.  
29.       verticesLeft = vertices.Sum(vertex => vertex.position.y);
30.     }
31.  
32.     Vertex[] flattenedVertices = m_Mesh.GetVertices()
33.      .Select(
34.         vertex => {
35.           Vector3 pos = vertex.position;
36.           vertex.position = new Vector3(pos.x, 0, pos.z);
37.  
38.           return vertex;
39.         }
40.       )
41.      .ToArray();
42.  
43.     m_Mesh.SetVertices(flattenedVertices);
44.     m_Mesh.ToMesh();
45.     m_Mesh.Refresh();
46.  
47.     MeshUtility.CollapseSharedVertices(m_Mesh.GetComponent<MeshFilter>().sharedMesh);
48.  
49.     StopCoroutine(flattenRoutine);
50.   }
51. }