HelixToolkit.Wpf.MeshBuilder.Subdivide4 C# (CSharp) Method

        private void Subdivide4()
        {
            // Each triangle is divided into four subtriangles, adding new vertices in the middle of each edge.
            int ip = this.Positions.Count;
            int ntri = this.TriangleIndices.Count;
            for (int i = 0; i < ntri; i += 3)
            {
                int i0 = this.TriangleIndices[i];
                int i1 = this.TriangleIndices[i + 1];
                int i2 = this.TriangleIndices[i + 2];
                var p0 = this.Positions[i0];
                var p1 = this.Positions[i1];
                var p2 = this.Positions[i2];
                var v01 = p1 - p0;
                var v12 = p2 - p1;
                var v20 = p0 - p2;
                var p01 = p0 + (v01 * 0.5);
                var p12 = p1 + (v12 * 0.5);
                var p20 = p2 + (v20 * 0.5);

                int i01 = ip++;
                int i12 = ip++;
                int i20 = ip++;

                this.Positions.Add(p01);
                this.Positions.Add(p12);
                this.Positions.Add(p20);

                if (this.normals != null)
                {
                    var n = this.Normals[i0];
                    this.Normals.Add(n);
                    this.Normals.Add(n);
                    this.Normals.Add(n);
                }

                if (this.textureCoordinates != null)
                {
                    var uv0 = this.TextureCoordinates[i0];
                    var uv1 = this.TextureCoordinates[i0 + 1];
                    var uv2 = this.TextureCoordinates[i0 + 2];
                    var t01 = uv1 - uv0;
                    var t12 = uv2 - uv1;
                    var t20 = uv0 - uv2;
                    var u01 = uv0 + (t01 * 0.5);
                    var u12 = uv1 + (t12 * 0.5);
                    var u20 = uv2 + (t20 * 0.5);
                    this.TextureCoordinates.Add(u01);
                    this.TextureCoordinates.Add(u12);
                    this.TextureCoordinates.Add(u20);
                }

                // TriangleIndices[i ] = i0;
                this.TriangleIndices[i + 1] = i01;
                this.TriangleIndices[i + 2] = i20;

                this.TriangleIndices.Add(i01);
                this.TriangleIndices.Add(i1);
                this.TriangleIndices.Add(i12);

                this.TriangleIndices.Add(i12);
                this.TriangleIndices.Add(i2);
                this.TriangleIndices.Add(i20);

                this.TriangleIndices.Add(i01);
                this.TriangleIndices.Add(i12);
                this.TriangleIndices.Add(i20);
            }
        }