Curved PN Triangles
April 2001 - Alex Vlachos, Jörg Peters
This article explains the Curved PN Triangles as they are implemented in DX8.
Implementing Curved Surface Geometry
June 1999 - Brian Sharp
NURB Curves: A Guide for the Uninitiated
Polar Forms and Triangular B-Spline Surfaces
Using NURBS Surfaces in Real-time Applications
Bézier Triangles and N-Patches
July 2002 - Tomas Akenine-Möller, Eric Haines
This article shows how to compute Bezier Triangles and how they are used to form N-Patches in current 3D graphics.