For subdividing meshes in Unity

Mesh Helper C#

public class MeshHelper
    {
        static List<Vector3> vertices;

        static List<Vector3> normals;
        // [... all other vertex data arrays you need]

        static List<int> indices;
        static Dictionary<uint, int> newVectices;

        static int GetNewVertex(int i1, int i2)
        {
            // We have to test both directions since the edge
            // could be reversed in another triangle
            uint t1 = ((uint) i1 << 16) | (uint) i2;
            uint t2 = ((uint) i2 << 16) | (uint) i1;
            if (newVectices.ContainsKey(t2))
                return newVectices[t2];
            if (newVectices.ContainsKey(t1))
                return newVectices[t1];
            // generate vertex:
            int newIndex = vertices.Count;
            newVectices.Add(t1, newIndex);

            // calculate new vertex
            vertices.Add((vertices[i1] + vertices[i2]) * 0.5f);
            normals.Add((normals[i1] + normals[i2]).normalized);
            // [... all other vertex data arrays]

            return newIndex;
        }


        public static void Subdivide(Mesh mesh)
        {
            newVectices = new Dictionary<uint, int>();

            vertices = new List<Vector3>(mesh.vertices);
            normals = new List<Vector3>(mesh.normals);
            // [... all other vertex data arrays]
            indices = new List<int>();

            int[] triangles = mesh.triangles;
            for (int i = 0; i < triangles.Length; i += 3)
            {
                int i1 = triangles[i + 0];
                int i2 = triangles[i + 1];
                int i3 = triangles[i + 2];

                int a = GetNewVertex(i1, i2);
                int b = GetNewVertex(i2, i3);
                int c = GetNewVertex(i3, i1);
                indices.Add(i1);
                indices.Add(a);
                indices.Add(c);
                indices.Add(i2);
                indices.Add(b);
                indices.Add(a);
                indices.Add(i3);
                indices.Add(c);
                indices.Add(b);
                indices.Add(a);
                indices.Add(b);
                indices.Add(c); // center triangle
            }

            mesh.vertices = vertices.ToArray();
            mesh.normals = normals.ToArray();
            // [... all other vertex data arrays]
            mesh.triangles = indices.ToArray();

            // since this is a static function and it uses static variables
            // we should erase the arrays to free them:
            newVectices = null;
            vertices = null;
            normals = null;
            // [... all other vertex data arrays]

            indices = null;
        }
    }