# gluNurbsSurface.3G - Man Page

define the shape of a NURBS surface

## C Specification

void gluNurbsSurface( GLUnurbs* nurb,

```	GLint sKnotCount,
GLfloat* sKnots,
GLint tKnotCount,
GLfloat* tKnots,
GLint sStride,
GLint tStride,
GLfloat* control,
GLint sOrder,
GLint tOrder,
GLenum type )```

## Parameters

nurb

Specifies the NURBS object (created with gluNewNurbsRenderer).

sKnotCount

Specifies the number of knots in the parametric u direction.

sKnots

Specifies an array of sKnotCount nondecreasing knot values in the parametric u direction.

tKnotCount

Specifies the number of knots in the parametric v direction.

tKnots

Specifies an array of tKnotCount nondecreasing knot values in the parametric v direction.

sStride

Specifies the offset (as a number of single-precision floating point values) between successive control points in the parametric u direction in control.

tStride

Specifies the offset (in single-precision floating-point values) between successive control points in the parametric v direction in control.

control

Specifies an array containing control points for the NURBS surface. The offsets between successive control points in the parametric u and v directions are given by sStride and tStride.

sOrder

Specifies the order of the NURBS surface in the parametric u  direction. The order is one more than the degree, hence a surface that is cubic in u has a u order of 4.

tOrder

Specifies the order of the NURBS surface in the parametric v  direction. The order is one more than the degree, hence a surface that is cubic in v has a v order of 4.

type

Specifies type of the surface. type can be any of the valid two-dimensional evaluator types (such as GL_MAP2_VERTEX_3 or  GL_MAP2_COLOR_4).

## Description

Use gluNurbsSurface within a NURBS (Non-Uniform Rational B-Spline) surface definition to describe the shape of a NURBS surface (before any trimming). To mark the beginning of  a NURBS surface definition, use the gluBeginSurface command. To mark the end of a NURBS surface definition, use the  gluEndSurface command. Call gluNurbsSurface within a NURBS surface definition only.

Positional, texture, and color coordinates are associated with a surface by presenting each as a separate gluNurbsSurface between a  gluBeginSurface/gluEndSurface pair. No more than one call to gluNurbsSurface for each of color, position, and texture data can be made within a single gluBeginSurface/gluEndSurface pair. Exactly one call must be made to describe the position of the  surface (a type of GL_MAP2_VERTEX_3 or GL_MAP2_VERTEX_4).

A NURBS surface can be trimmed by using the commands  gluNurbsCurve and gluPwlCurve between calls to gluBeginTrim and gluEndTrim.

Note that a gluNurbsSurface with sKnotCount knots in the u direction and tKnotCount knots in the v direction with orders  sOrder and tOrder must have  (sKnotCount - sOrder) $×$ (tKnotCount - tOrder) control points.

## Example

The following commands render a textured NURBS surface with normals; the texture coordinates and normals are also NURBS surfaces:

gluBeginSurface(nobj);
gluNurbsSurface(nobj, ..., GL_MAP2_TEXTURE_COORD_2);
gluNurbsSurface(nobj, ..., GL_MAP2_NORMAL);
gluNurbsSurface(nobj, ..., GL_MAP2_VERTEX_4); gluEndSurface(nobj);