/// <summary>
/// Returns a vector which is on the same plane as the polygon, and perpendiculat to the nth edge
/// </summary>
/// <param name="poly"></param>
/// <param name="index"></param>
/// <returns></returns>
public static Vector3 GetSurfaceNormal(this IPoly poly, int index)
{
if (poly is IPolyExtensionSurfaceNormal)
{
return(((IPolyExtensionSurfaceNormal)poly).AdvGetSurfaceNormal(index));
}
else if (poly is IPolyForwarder)
{
return(((IPolyForwarder)poly).GetPoly().GetSurfaceNormal(index));
}
else
{
return(poly.CalcSurfaceNormal(index));
}
}