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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
<refentry id="gluBeginSurface">
<refmeta>
<refmetainfo>
<copyright>
<year>1991-2006</year>
<holder>Silicon Graphics, Inc.</holder>
</copyright>
</refmetainfo>
<refentrytitle>gluBeginSurface</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>gluBeginSurface</refname>
<refpurpose>delimit a NURBS surface definition</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>gluBeginSurface</function></funcdef>
<paramdef>GLUnurbs* <parameter>nurb</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>gluEndSurface</function></funcdef>
<paramdef>GLUnurbs* <parameter>nurb</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<!-- eqn: ignoring delim $$ -->
<refsect1 id="parameters"><title>Parameters</title>
<variablelist>
<varlistentry>
<term><parameter>nurb</parameter></term>
<listitem>
<para>
Specifies the NURBS object (created with <citerefentry><refentrytitle>gluNewNurbsRenderer</refentrytitle></citerefentry>).
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="description"><title>Description</title>
<para>
Use <function>gluBeginSurface</function> to mark the beginning of a NURBS
surface definition. After
calling <function>gluBeginSurface</function>, make one or more calls to
<citerefentry><refentrytitle>gluNurbsSurface</refentrytitle></citerefentry> to define the attributes of the surface.
Exactly one of these calls to <citerefentry><refentrytitle>gluNurbsSurface</refentrytitle></citerefentry> must have a
surface type of <constant>GLU_MAP2_VERTEX_3</constant> or <constant>GLU_MAP2_VERTEX_4</constant>.
To mark the end of the NURBS surface definition, call
<citerefentry><refentrytitle>gluEndSurface</refentrytitle></citerefentry>.
</para>
<para>
Trimming of NURBS surfaces is supported with <citerefentry><refentrytitle>gluBeginTrim</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>gluPwlCurve</refentrytitle></citerefentry>, <citerefentry><refentrytitle>gluNurbsCurve</refentrytitle></citerefentry>, and <citerefentry><refentrytitle>gluEndTrim</refentrytitle></citerefentry>. See the
<citerefentry><refentrytitle>gluBeginTrim</refentrytitle></citerefentry> reference page for details.
</para>
<para>
GL evaluators are used to render the NURBS surface as a set of polygons.
Evaluator state is preserved during rendering
with <citerefentry><refentrytitle>glPushAttrib</refentrytitle></citerefentry>(<constant>GLU_EVAL_BIT</constant>) and
<citerefentry><refentrytitle>glPopAttrib</refentrytitle></citerefentry>.
See the <citerefentry><refentrytitle>glPushAttrib</refentrytitle></citerefentry> reference page for details on exactly what state
these calls preserve.
</para>
</refsect1>
<refsect1 id="example"><title>Example</title>
<para>
The following commands render a textured NURBS surface with normals;
the texture coordinates and normals are also described as NURBS surfaces:
<programlisting>
gluBeginSurface(nobj);
gluNurbsSurface(nobj, ..., GL_MAP2_TEXTURE_COORD_2);
gluNurbsSurface(nobj, ..., GL_MAP2_NORMAL);
gluNurbsSurface(nobj, ..., GL_MAP2_VERTEX_4);
gluEndSurface(nobj);
</programlisting>
</para>
</refsect1>
<refsect1 id="seealso"><title>See Also</title>
<para>
<citerefentry><refentrytitle>gluBeginCurve</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>gluBeginTrim</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>gluNewNurbsRenderer</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>gluNurbsCurve</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>gluNurbsSurface</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>gluPwlCurve</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glPushAttrib</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"></trademark> 1991-2006
Silicon Graphics, Inc. This document is licensed under the SGI
Free Software B License. For details, see
<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
</para>
</refsect1>
</refentry>