public static void AddRegularPolygon(this MeshGeometry3D mesh,
int numSides, Point3D center, Vector3D vx, Vector3D vy,
Dictionary <Point3D, int> pointDict = null,
Point[] textureCoords = null)
{
// Generate the points.
Point3D[] points = G3.MakePolygonPoints(numSides, center, vx, vy);
// Make the polygon.
mesh.AddPolygon(points, textureCoords);
}