_C_ License Applicability. Except to the extent portions of this file are
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_C_ Software License B, Version 1.1 (the "License"), the contents of this
_C_ file are subject only to the provisions of the License. You may not use
_C_ this file except in compliance with the License. You may obtain a copy
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_C_ 
_C_ http://oss.sgi.com/projects/FreeB
_C_ 
_C_ Note that, as provided in the License, the Software is distributed on an
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_C_ 
_C_ Original Code. The Original Code is: OpenGL Sample Implementation,
_C_ Version 1.2.1, released January 26, 2000, developed by Silicon Graphics,
_C_ Inc. The Original Code is Copyright (c) 1991-2000 Silicon Graphics, Inc.
_C_ Copyright in any portions created by third parties is as indicated
_C_ elsewhere herein. All Rights Reserved.
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_C_ Additional Notice Provisions: The application programming interfaces
_C_ established by SGI in conjunction with the Original Code are The
_C_ OpenGL(R) Graphics System: A Specification (Version 1.2.1), released
_C_ April 1, 1999; The OpenGL(R) Graphics System Utility Library (Version
_C_ 1.3), released November 4, 1998; and OpenGL(R) Graphics with the X
_C_ Window System(R) (Version 1.3), released October 19, 1998. This software
_C_ was created using the OpenGL(R) version 1.2.1 Sample Implementation
_C_ published by SGI, but has not been independently verified as being
_C_ compliant with the OpenGL(R) version 1.2.1 Specification.
_C_
_C_ $Date$ $Revision$
_C_ The first character in this file must be an '_'!
_C_ Anything on a line after _C_ is ignored
_define(_filters,eqn)_C_
_C_      eqn is automatically replaced with neqn for nroff
_header(BeginSurface, delimit a NURBS surface definition)
_names(BeginSurface)
_names(EndSurface,,noheader)
.EQ
delim $$
.EN
.SH PARAMETERS
_phead(_param1)
Specifies the NURBS object (created with _cmnd(NewNurbsRenderer)).
.SH DESCRIPTION
Use _cmnd(BeginSurface) to mark the beginning of a NURBS 
surface definition. After 
calling _cmnd(BeginSurface), make one or more calls to
_cmnd(NurbsSurface) to define the attributes of the surface.
Exactly one of these calls to _cmnd(NurbsSurface) must have a
surface type of _const(MAP2_VERTEX_3) or _const(MAP2_VERTEX_4).
To mark the end of the NURBS surface definition, call
_cmnd(EndSurface).
.P
Trimming of NURBS surfaces is supported with _cmnd(BeginTrim), 
_cmnd(PwlCurve), _cmnd(NurbsCurve), and _cmnd(EndTrim). See the
_cmnd(BeginTrim) reference page for details.
.P
GL evaluators are used to render the NURBS surface as a set of polygons.
Evaluator state is preserved during rendering
with _glcmnd(PushAttrib)(_const(EVAL_BIT)) and 
_glcmnd(PopAttrib)().  
See the _glcmnd(PushAttrib) reference page for details on exactly what state
these calls preserve.
.SH EXAMPLE
The following commands render a textured NURBS surface with normals;
the texture coordinates and normals are also described as NURBS surfaces:
.sp
.Ex
gluBeginSurface(nobj);
   gluNurbsSurface(nobj, ..., GL_MAP2_TEXTURE_COORD_2);
   gluNurbsSurface(nobj, ..., GL_MAP2_NORMAL);
   gluNurbsSurface(nobj, ..., GL_MAP2_VERTEX_4);
gluEndSurface(nobj);
.Ee
.sp
.SH SEE ALSO
_cmnd(BeginCurve), _cmnd(BeginTrim), _cmnd(NewNurbsRenderer), 
_cmnd(NurbsCurve), _cmnd(NurbsSurface), _cmnd(PwlCurve)



