
<refentry id="gluNurbsCurve">
    <refmeta>
        <refmetainfo>
            <copyright>
                <year>1991-2006</year>
                <holder>Silicon Graphics, Inc.</holder>
            </copyright>
        </refmetainfo>
        <refentrytitle>gluNurbsCurve</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>gluNurbsCurve</refname>
        <refpurpose>define the shape of a NURBS curve</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>gluNurbsCurve</function></funcdef>
                <paramdef>GLUnurbs* <parameter>nurb</parameter></paramdef>
                <paramdef>GLint <parameter>knotCount</parameter></paramdef>
                <paramdef>GLfloat * <parameter>knots</parameter></paramdef>
                <paramdef>GLint <parameter>stride</parameter></paramdef>
                <paramdef>GLfloat * <parameter>control</parameter></paramdef>
                <paramdef>GLint <parameter>order</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>knotCount</parameter></term>
            <listitem>
                <para>
                    Specifies the number of knots in <parameter>knots</parameter>.
                    <parameter>knotCount</parameter> equals the number of control points plus the order.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>knots</parameter></term>
            <listitem>
                <para>
                    Specifies an array of <parameter>knotCount</parameter> nondecreasing knot values.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>stride</parameter></term>
            <listitem>
                <para>
                    Specifies the offset (as a number of single-precision floating-point values)
                    between successive curve control points.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>control</parameter></term>
            <listitem>
                <para>
                    Specifies a pointer to an array of control points. The coordinates must
                    agree with <parameter>type</parameter>, specified below.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>order</parameter></term>
            <listitem>
                <para>
                    Specifies the order of the NURBS curve. <parameter>order</parameter> equals degree + 1, hence
                    a cubic curve has an order of 4.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>type</parameter></term>
            <listitem>
                <para>
                    Specifies the type of the curve. If this curve is defined within a 
                    <citerefentry><refentrytitle>gluBeginCurve</refentrytitle></citerefentry>/<citerefentry><refentrytitle>gluEndCurve</refentrytitle></citerefentry> pair, then 
                    the type can be any of the valid
                    one-dimensional evaluator types (such as <constant>GLU_MAP1_VERTEX_3</constant> or 
                    <constant>GLU_MAP1_COLOR_4</constant>). Between a <citerefentry><refentrytitle>gluBeginTrim</refentrytitle></citerefentry>/<citerefentry><refentrytitle>gluEndTrim</refentrytitle></citerefentry> pair,
                    the only valid types are <constant>GLU_MAP1_TRIM_2</constant> and <constant>GLU_MAP1_TRIM_3</constant>.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
        <para>
            Use <function>gluNurbsCurve</function> to describe a NURBS curve.
        </para>
        <para>
            When <function>gluNurbsCurve</function> appears between a <citerefentry><refentrytitle>gluBeginCurve</refentrytitle></citerefentry>/<citerefentry><refentrytitle>gluEndCurve</refentrytitle></citerefentry> pair, it is 
            used to describe a curve to be rendered.
            Positional, texture, and color coordinates are associated
            by presenting each as a separate <function>gluNurbsCurve</function> between a 
            <citerefentry><refentrytitle>gluBeginCurve</refentrytitle></citerefentry>/<citerefentry><refentrytitle>gluEndCurve</refentrytitle></citerefentry> pair. No more than
            one call to <function>gluNurbsCurve</function> for each of color, position, and texture
            data can be made within a single <citerefentry><refentrytitle>gluBeginCurve</refentrytitle></citerefentry>/<citerefentry><refentrytitle>gluEndCurve</refentrytitle></citerefentry>
            pair. Exactly one call must be made to describe the position of the 
            curve (a <parameter>type</parameter> of <constant>GLU_MAP1_VERTEX_3</constant> or <constant>GLU_MAP1_VERTEX_4</constant>).
        </para>
        <para>
            When <function>gluNurbsCurve</function> appears between a <citerefentry><refentrytitle>gluBeginTrim</refentrytitle></citerefentry>/<citerefentry><refentrytitle>gluEndTrim</refentrytitle></citerefentry> pair, it is 
            used to describe a trimming curve on a NURBS surface. If <parameter>type</parameter> is
            <constant>GLU_MAP1_TRIM_2</constant>, then it describes a curve in two-dimensional (<emphasis>u</emphasis> 
            and <emphasis>v</emphasis>)
            parameter space. If it is <constant>GLU_MAP1_TRIM_3</constant>, then it describes a 
            curve in two-dimensional homogeneous (<emphasis>u</emphasis>, <emphasis>v</emphasis>, and <emphasis>w</emphasis>) 
            parameter space.
            See the <citerefentry><refentrytitle>gluBeginTrim</refentrytitle></citerefentry> reference page for more discussion about trimming
            curves.
        </para>
    </refsect1>
    <refsect1 id="example"><title>Example</title>
        <para>
            The following commands render a textured NURBS curve with normals:
            <programlisting>
gluBeginCurve(nobj);
   gluNurbsCurve(nobj, ..., GL_MAP1_TEXTURE_COORD_2);
   gluNurbsCurve(nobj, ..., GL_MAP1_NORMAL);
   gluNurbsCurve(nobj, ..., GL_MAP1_VERTEX_4);
gluEndCurve(nobj);
            </programlisting>
        </para>
    </refsect1>
    <refsect1 id="notes"><title>Notes</title>
        <para>
            To define trim curves that stitch well, use <citerefentry><refentrytitle>gluPwlCurve</refentrytitle></citerefentry>.
        </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>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>
