1991-2006
Silicon Graphics, Inc.
gluNurbsCurve
3G

# gluNurbsCurve

define the shape of a NURBS curve

## C Specification

                    void gluNurbsCurve
                    GLUnurbs* nurb
                    GLint knotCount
                    GLfloat * knots
                    GLint stride
                    GLfloat * control
                    GLint order
                    GLenum type

## Parameters

`nurb`

  Specifies the NURBS object (created with gluNewNurbsRenderer).

`knotCount`

  Specifies the number of knots in `knots`. `knotCount` equals the number of control points plus the order.

`knots`

  Specifies an array of `knotCount` nondecreasing knot values.

`stride`

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

`control`

  Specifies a pointer to an array of control points. The coordinates must agree with `type`, specified below.

`order`

  Specifies the order of the NURBS curve. `order` equals degree + 1, hence a cubic curve has an order of 4.

`type`

  Specifies the type of the curve. If this curve is defined within a gluBeginCurve/gluEndCurve pair, then the type can be any of the valid one-dimensional evaluator types (such as `GLU_MAP1_VERTEX_3` or `GLU_MAP1_COLOR_4`). Between a gluBeginTrim/gluEndTrim pair, the only valid types are `GLU_MAP1_TRIM_2` and `GLU_MAP1_TRIM_3`.

## Description

Use `gluNurbsCurve` to describe a NURBS curve.

When `gluNurbsCurve` appears between a gluBeginCurve/gluEndCurve pair, it is used to describe a curve to be rendered. Positional, texture, and color coordinates are associated by presenting each as a separate `gluNurbsCurve` between a gluBeginCurve/gluEndCurve pair. No more than one call to `gluNurbsCurve` for each of color, position, and texture data can be made within a single gluBeginCurve/gluEndCurve pair. Exactly one call must be made to describe the position of the curve (a `type` of `GLU_MAP1_VERTEX_3` or `GLU_MAP1_VERTEX_4`).

When `gluNurbsCurve` appears between a gluBeginTrim/gluEndTrim pair, it is used to describe a trimming curve on a NURBS surface. If `type` is `GLU_MAP1_TRIM_2`, then it describes a curve in two-dimensional (u and v) parameter space. If it is `GLU_MAP1_TRIM_3`, then it describes a curve in two-dimensional homogeneous (u, v, and w) parameter space. See the gluBeginTrim reference page for more discussion about trimming curves.

## Example

The following commands render a textured NURBS curve with normals:

    gluBeginCurve(nobj);
       gluNurbsCurve(nobj, ..., GL_MAP1_TEXTURE_COORD_2);
       gluNurbsCurve(nobj, ..., GL_MAP1_NORMAL);
       gluNurbsCurve(nobj, ..., GL_MAP1_VERTEX_4);
    gluEndCurve(nobj);

## Notes

To define trim curves that stitch well, use gluPwlCurve.

## See Also

gluBeginCurve, gluBeginTrim, gluNewNurbsRenderer, 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/.