
<refentry id="gluNurbsSurface">
    <refmeta>
        <refmetainfo>
            <copyright>
                <year>1991-2006</year>
                <holder>Silicon Graphics, Inc.</holder>
            </copyright>
        </refmetainfo>
        <refentrytitle>gluNurbsSurface</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>gluNurbsSurface</refname>
        <refpurpose>define the shape of a NURBS surface</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>gluNurbsSurface</function></funcdef>
                <paramdef>GLUnurbs* <parameter>nurb</parameter></paramdef>
                <paramdef>GLint <parameter>sKnotCount</parameter></paramdef>
                <paramdef>GLfloat* <parameter>sKnots</parameter></paramdef>
                <paramdef>GLint <parameter>tKnotCount</parameter></paramdef>
                <paramdef>GLfloat* <parameter>tKnots</parameter></paramdef>
                <paramdef>GLint <parameter>sStride</parameter></paramdef>
                <paramdef>GLint <parameter>tStride</parameter></paramdef>
                <paramdef>GLfloat* <parameter>control</parameter></paramdef>
                <paramdef>GLint <parameter>sOrder</parameter></paramdef>
                <paramdef>GLint <parameter>tOrder</parameter></paramdef>
                <paramdef>GLenum <parameter>type</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>
        <varlistentry>
            <term><parameter>sKnotCount</parameter></term>
            <listitem>
                <para>
                    Specifies the number of knots in the parametric <emphasis>u</emphasis> direction.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>sKnots</parameter></term>
            <listitem>
                <para>
                    Specifies an array of <parameter>sKnotCount</parameter> nondecreasing knot values in the parametric
                    <emphasis>u</emphasis> direction.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>tKnotCount</parameter></term>
            <listitem>
                <para>
                    Specifies the number of knots in the parametric <emphasis>v</emphasis> direction.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>tKnots</parameter></term>
            <listitem>
                <para>
                    Specifies an array of <parameter>tKnotCount</parameter> nondecreasing knot values in the parametric
                    <emphasis>v</emphasis> direction.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>sStride</parameter></term>
            <listitem>
                <para>
                    Specifies the offset (as a number of single-precision floating-point values)
                    between successive control points in the parametric <emphasis>u</emphasis> direction
                    in <parameter>control</parameter>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>tStride</parameter></term>
            <listitem>
                <para>
                    Specifies the offset (in single-precision floating-point values)
                    between successive control points in the parametric <emphasis>v</emphasis> direction
                    in <parameter>control</parameter>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>control</parameter></term>
            <listitem>
                <para>
                    Specifies an array containing control points for the NURBS surface.
                    The offsets between successive control points in the parametric <emphasis>u</emphasis>
                    and <emphasis>v</emphasis> directions are given by <parameter>sStride</parameter> and <parameter>tStride</parameter>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>sOrder</parameter></term>
            <listitem>
                <para>
                    Specifies the order of the NURBS surface in the parametric <emphasis>u</emphasis> 
                    direction. The order is one more than the degree, hence
                    a surface that is cubic in <emphasis>u</emphasis> has a <emphasis>u</emphasis> order of 4.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>tOrder</parameter></term>
            <listitem>
                <para>
                    Specifies the order of the NURBS surface in the parametric <emphasis>v</emphasis> 
                    direction. The order is one more than the degree, hence
                    a surface that is cubic in <emphasis>v</emphasis> has a <emphasis>v</emphasis> order of 4.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>type</parameter></term>
            <listitem>
                <para>
                    Specifies type of the surface. <parameter>type</parameter> can be any of the valid
                    two-dimensional evaluator types (such as <constant>GLU_MAP2_VERTEX_3</constant> or 
                    <constant>GLU_MAP2_COLOR_4</constant>).
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
        <para>
            Use <function>gluNurbsSurface</function> 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 <citerefentry><refentrytitle>gluBeginSurface</refentrytitle></citerefentry> command.
            To mark the end of a NURBS surface definition, use the 
            <citerefentry><refentrytitle>gluEndSurface</refentrytitle></citerefentry> command. Call <function>gluNurbsSurface</function> within a NURBS
            surface definition only.
        </para>
        <para>
            Positional, texture, and color coordinates are associated
            with a surface by presenting each as a separate <function>gluNurbsSurface</function> between a 
            <citerefentry><refentrytitle>gluBeginSurface</refentrytitle></citerefentry>/<citerefentry><refentrytitle>gluEndSurface</refentrytitle></citerefentry> pair. No more than
            one call to <function>gluNurbsSurface</function> for each of color, position, and texture
            data can be made within a single <citerefentry><refentrytitle>gluBeginSurface</refentrytitle></citerefentry>/<citerefentry><refentrytitle>gluEndSurface</refentrytitle></citerefentry>
            pair. Exactly one call must be made to describe the position of the 
            surface (a <parameter>type</parameter> of <constant>GLU_MAP2_VERTEX_3</constant> or <constant>GLU_MAP2_VERTEX_4</constant>).
        </para>
        <para>
            A NURBS surface can be trimmed by using the commands 
            <citerefentry><refentrytitle>gluNurbsCurve</refentrytitle></citerefentry> and <citerefentry><refentrytitle>gluPwlCurve</refentrytitle></citerefentry> between calls to
            <citerefentry><refentrytitle>gluBeginTrim</refentrytitle></citerefentry> and <citerefentry><refentrytitle>gluEndTrim</refentrytitle></citerefentry>.
        </para>
        <para>
            Note that a <function>gluNurbsSurface</function> with <parameter>sKnotCount</parameter> knots in the <emphasis>u</emphasis> direction
            and <parameter>tKnotCount</parameter> knots in the <emphasis>v</emphasis> direction with orders 
            <parameter>sOrder</parameter> and <parameter>tOrder</parameter> must have 
            (<parameter>sKnotCount</parameter> - <parameter>sOrder</parameter>) 
            <inlineequation><mml:math><mml:mi mathvariant="italic">times</mml:mi></mml:math></inlineequation>
            (<parameter>tKnotCount</parameter> - <parameter>tOrder</parameter>) control points.
        </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 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>gluBeginSurface</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>gluBeginTrim</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>gluNewNurbsRenderer</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>gluNurbsCurve</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>gluPwlCurve</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>
