说明：  OpenGL编程轻松入门之NURBS曲线和曲面.此例绘制两个相同形状的NURBS曲面，不同之处是一个为线框式，一个是由实多边形组成。
(OpenGL programming easy entry of NURBS curves and surfaces. In this case, the shape of two identical rendering NURBS surfaces, the only difference is a frame type, a polygon is formed by.)