1991-2006
Silicon Graphics, Inc.
gluNurbsSurface
3G

# gluNurbsSurface

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 `GLU_MAP2_VERTEX_3` or `GLU_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 `GLU_MAP2_VERTEX_3` or `GLU_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`) times (`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);

## See Also

gluBeginSurface, gluBeginTrim, gluNewNurbsRenderer, gluNurbsCurve, gluPwlCurve

## Copyright

Copyright 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.