The OpenGL functions for drawing NURBS curves are very similar to the IRIS GL functions. You specify knot sequences and control points using a gluNurbsCurve function, which must be contained within a gluBeginCurve/gluEndCurve pair.
The following table lists the IRIS GL functions for drawing NURBS curves and their equivalent OpenGL functions.
| IRIS GL Function | OpenGL Function | Meaning |
|---|---|---|
| bgncurve | gluBeginCurve | Begin a curve definition. |
| nurbscurve | gluNurbsCurve | Specify curve attributes. |
| endcurve | gluEndCurve | End a curve definition. |
Associate position, texture, and color coordinates by presenting each as a separate gluNurbsCurve inside the begin/end pair. You can make no more than one call to gluNurbsCurve for each piece of color, position, and texture data within a single gluBeginCurve/gluEndCurve pair. You must make exactly one call to describe the position of the curve (a GL_MAP1_VERTEX_3 or GL_MAP1_VERTEX_4 description). When you call gluEndCurve, the curve is tessellated into line segments and then rendered.
The following table lists IRIS GL and OpenGL NURBS curve types.
| IRIS GL Type | OpenGL Type | Meaning |
|---|---|---|
| N_V3D | GL_MAP1_VERTEX_3 | Polynomial curve. |
| N_V3DR | GL_MAP1_VERTEX_4 | Rational curve. |
| — | GL_MAP1_TEXTURE_COORD_* | Control points are texture coordinates. |
| — | GL_MAP1_NORMAL | Control points are normals. |
For more information on available evaluator types, see glMap1.