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gluNurbsSurface - define the shape of a NURBS surface 
 
void
gluNurbsSurface( GLUnurbs* nurb, 
    GLint sKnotCount,
    GLfloat* sKnots,
    GLint tKnotCount,
    GLfloat* tKnots,
    GLint sStride,
    GLint tStride,
    GLfloat* control,
    GLint sOrder,
    GLint tOrder,
    GLenum type )
 eqn not supported
- 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).
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)
$times$ (tKnotCount - tOrder) control points. 
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)
;  
gluBeginSurface(3G)
, gluBeginTrim(3G)
, gluNewNurbsRenderer(3G)
,
 gluNurbsCurve(3G)
, gluPwlCurve(3G)
 
 
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