Procedural Geometry - Tris

I am making a system, where shapes can be made at runtime, and adopt vertices and triangles to create a procedural shape. These shapes are defined by the users mouse movement.

I am not understanding if there is a foolproof way to create the tris, so that they can create the tris in the places, even when shapes are different i.e. if a shape is a kite, triangle, or something more abstract.

I know that the triangle array should contain a length divisible by 3, but cannot see a one size fits all solution to the problem. Any help would be appriciated.

Code (CSharp):

1.     void CreateShape()
2.     {
3.         GameObject go = new GameObject();
4.         go.AddComponent<MeshFilter>();
5.         go.AddComponent<MeshRenderer>();
6.         go.transform.localScale *= 2.5f;
7.  
8.         Mesh mesh = new Mesh();
9.  
10.         Vector3[] vertices = new Vector3[selectedNodes.Count];
11.         int[] tris = new int[selectedNodes.Count];
12.  
13.         for(int i = 0; i < vertices.Length; i++)
14.         {
15.             vertices[i] = new Vector3(selectedNodes[i].xPos, selectedNodes[i].yPos, 0f);
16.             tris[i] = i;
17.         }
18.  
19.         mesh.vertices = vertices;
20.         mesh.triangles = tris;
21.  
22.         go.GetComponent<MeshFilter>().mesh = mesh;
23.     }

 

A square is 2 tris (your tri list will have six indices), a pentagon is 3 tris (9 indixes), etc

This is called 'Triangulation' and there are dozens of resources available on performing it

 

It sounds a bit like you want the user to draw a series of points and then wrap a convex hull around that (and triangulate it internally). A good algorithm for that is Delaunay triangulation (http://www.qhull.org/)

Here's a javascript example of convex hull creation: https://www.nayuki.io/page/convex-hull-algorithm

And a javascript example of delaunay triangulation: https://github.com/mapbox/delaunator