public static Mesh generate(int triangle_budget)
        {
            Mesh original_mesh = TessellatedMesh.generate(Octahedron.octahedron_mesh(), triangle_budget, 1)[0];

            Vector2[] uvs = new Vector2[original_mesh.vertices.Length];
            for (int vertex = 0; vertex < original_mesh.vertices.Length; vertex += 1)
            {
                if (original_mesh.vertices[vertex] != Vector3.down) // almost every point uses polar coordinates from the underlying texture
                {
                    float   angle  = Vector3.SignedAngle(Vector3.right, Vector3.ProjectOnPlane(original_mesh.vertices[vertex], Vector3.up).normalized, Vector3.up) * Mathf.Deg2Rad;
                    float   radius = Vector3.Angle(Vector3.up, original_mesh.vertices[vertex]) * Mathf.Deg2Rad;
                    Vector2 uv     = new Vector2(Mathf.Cos(angle), Mathf.Sin(angle));
                    uv         *= (radius / Mathf.PI);
                    uv          = uv / 2 + new Vector2(0.5f, 0.5f);
                    uvs[vertex] = uv;
                }
                else // for points at 2PI, the four corners are identical and need to be handled separately.
                {
                    if (original_mesh.uv[vertex] == Vector2.one)
                    {
                        uvs[vertex] = (new Vector2(+1, +1)).normalized;
                    }
                    else if (original_mesh.uv[vertex] == Vector2.up)
                    {
                        uvs[vertex] = (new Vector2(-1, +1)).normalized;
                    }
                    else if (original_mesh.uv[vertex] == Vector2.zero)
                    {
                        uvs[vertex] = (new Vector2(-1, -1)).normalized;
                    }
                    else //if (original_mesh.uv[vertex] == Vector2.right)
                    {
                        uvs[vertex] = (new Vector2(+1, -1)).normalized;
                    }
                }
            }
            original_mesh.uv = uvs;
            return(original_mesh);
        }
 public static Mesh generate(int triangle_budget)
 {
     return(TessellatedMesh.generate(Octahedron.octahedron_mesh(), triangle_budget, 1)[0]);
 }