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363 lines
18 KiB
XML
363 lines
18 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
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"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
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<refentry id="glEvalCoord">
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<refmeta>
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<refmetainfo>
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<copyright>
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<year>1991-2006</year>
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<holder>Silicon Graphics, Inc.</holder>
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</copyright>
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</refmetainfo>
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<refentrytitle>glEvalCoord</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glEvalCoord</refname>
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<refpurpose>evaluate enabled one- and two-dimensional maps</refpurpose>
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</refnamediv>
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<!-- eqn: ignoring delim $$ -->
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glEvalCoord1f</function></funcdef>
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<paramdef>GLfloat <parameter>u</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glEvalCoord1d</function></funcdef>
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<paramdef>GLdouble <parameter>u</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glEvalCoord2f</function></funcdef>
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<paramdef>GLfloat <parameter>u</parameter></paramdef>
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<paramdef>GLfloat <parameter>v</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glEvalCoord2d</function></funcdef>
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<paramdef>GLdouble <parameter>u</parameter></paramdef>
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<paramdef>GLdouble <parameter>v</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1 id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>u</parameter></term>
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<listitem>
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<para>
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Specifies a value that is the domain coordinate
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<inlineequation><mml:math><mml:mi mathvariant="italic">u</mml:mi></mml:math></inlineequation>
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to the basis function
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defined in a previous <citerefentry><refentrytitle>glMap1</refentrytitle></citerefentry> or <citerefentry><refentrytitle>glMap2</refentrytitle></citerefentry> command.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>v</parameter></term>
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<listitem>
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<para>
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Specifies a value that is the domain coordinate
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<inlineequation><mml:math><mml:mi mathvariant="italic">v</mml:mi></mml:math></inlineequation>
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to the basis function
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defined in a previous <citerefentry><refentrytitle>glMap2</refentrytitle></citerefentry> command.
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This argument is not present in a <function>glEvalCoord1</function> command.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glEvalCoord1fv</function></funcdef>
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<paramdef>const GLfloat * <parameter>u</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glEvalCoord1dv</function></funcdef>
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<paramdef>const GLdouble * <parameter>u</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glEvalCoord2fv</function></funcdef>
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<paramdef>const GLfloat * <parameter>u</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glEvalCoord2dv</function></funcdef>
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<paramdef>const GLdouble * <parameter>u</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1 id="parameters2"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>u</parameter></term>
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<listitem>
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<para>
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Specifies a pointer to an array containing
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either one or two domain coordinates.
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The first coordinate is
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<inlineequation><mml:math><mml:mi mathvariant="italic">u</mml:mi></mml:math></inlineequation>.
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The second coordinate is
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<inlineequation><mml:math><mml:mi mathvariant="italic">v</mml:mi></mml:math></inlineequation>,
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which is present only in <function>glEvalCoord2</function> versions.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id="description"><title>Description</title>
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<para>
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<function>glEvalCoord1</function> evaluates enabled one-dimensional maps at argument
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<parameter>u</parameter>.
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<function>glEvalCoord2</function> does the same for two-dimensional maps using
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two domain values,
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<parameter>u</parameter> and <parameter>v</parameter>.
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To define a map, call <citerefentry><refentrytitle>glMap1</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glMap2</refentrytitle></citerefentry>; to enable and
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disable it, call <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry>.
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</para>
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<para>
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When one of the <function>glEvalCoord</function> commands is issued,
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all currently enabled maps of the indicated dimension are evaluated.
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Then,
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for each enabled map,
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it is as if the corresponding GL command had been issued with the
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computed value.
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That is,
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if <constant>GL_MAP1_INDEX</constant> or
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<constant>GL_MAP2_INDEX</constant> is enabled,
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a <citerefentry><refentrytitle>glIndex</refentrytitle></citerefentry> command is simulated.
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If <constant>GL_MAP1_COLOR_4</constant> or
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<constant>GL_MAP2_COLOR_4</constant> is enabled,
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a <citerefentry><refentrytitle>glColor</refentrytitle></citerefentry> command is simulated.
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If <constant>GL_MAP1_NORMAL</constant> or <constant>GL_MAP2_NORMAL</constant> is enabled,
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a normal vector is produced,
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and if any of
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<constant>GL_MAP1_TEXTURE_COORD_1</constant>,
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<constant>GL_MAP1_TEXTURE_COORD_2</constant>,
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<constant>GL_MAP1_TEXTURE_COORD_3</constant>,
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<constant>GL_MAP1_TEXTURE_COORD_4</constant>,
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<constant>GL_MAP2_TEXTURE_COORD_1</constant>,
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<constant>GL_MAP2_TEXTURE_COORD_2</constant>,
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<constant>GL_MAP2_TEXTURE_COORD_3</constant>, or
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<constant>GL_MAP2_TEXTURE_COORD_4</constant> is enabled, then an appropriate <citerefentry><refentrytitle>glTexCoord</refentrytitle></citerefentry> command is simulated.
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</para>
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<para>
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For color,
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color index,
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normal,
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and texture coordinates the GL uses evaluated values instead of current values for those evaluations
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that are enabled,
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and current values otherwise,
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However,
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the evaluated values do not update the current values.
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Thus, if <citerefentry><refentrytitle>glVertex</refentrytitle></citerefentry> commands are interspersed with <function>glEvalCoord</function>
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commands, the color,
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normal,
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and texture coordinates associated with the <citerefentry><refentrytitle>glVertex</refentrytitle></citerefentry> commands are not
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affected by the values generated by the <function>glEvalCoord</function> commands,
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but only by the most recent
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<citerefentry><refentrytitle>glColor</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glIndex</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glNormal</refentrytitle></citerefentry>, and
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<citerefentry><refentrytitle>glTexCoord</refentrytitle></citerefentry> commands.
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</para>
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<para>
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No commands are issued for maps that are not enabled.
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If more than one texture evaluation is enabled for a particular dimension
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(for example, <constant>GL_MAP2_TEXTURE_COORD_1</constant> and
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<constant>GL_MAP2_TEXTURE_COORD_2</constant>),
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then only the evaluation of the map that produces the larger
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number of coordinates
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(in this case, <constant>GL_MAP2_TEXTURE_COORD_2</constant>)
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is carried out.
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<constant>GL_MAP1_VERTEX_4</constant> overrides <constant>GL_MAP1_VERTEX_3</constant>,
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and
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<constant>GL_MAP2_VERTEX_4</constant> overrides <constant>GL_MAP2_VERTEX_3</constant>,
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in the same manner.
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If neither a three- nor a four-component vertex map is enabled for the
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specified dimension,
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the <function>glEvalCoord</function> command is ignored.
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</para>
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<para>
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If you have enabled automatic normal generation,
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by calling <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> with argument <constant>GL_AUTO_NORMAL</constant>,
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<function>glEvalCoord2</function> generates surface normals analytically,
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regardless of the contents or enabling of the <constant>GL_MAP2_NORMAL</constant> map.
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Let
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</para>
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<para>
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<informalequation><mml:math>
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<!-- eqn: bold m = { {partial bold p} over {partial u} } times { {partial bold p} over {partial v} }:-->
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<mml:mrow>
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<mml:mi mathvariant="bold">m</mml:mi>
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<mml:mo>=</mml:mo>
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<mml:mrow>
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<mml:mfenced open="" close="">
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<mml:mfrac>
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<mml:mfenced open="" close="">
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<mml:mrow>
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<mml:mo>∂</mml:mo>
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<mml:mi mathvariant="bold">p</mml:mi>
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</mml:mrow>
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</mml:mfenced>
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<mml:mfenced open="" close="">
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<mml:mrow>
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<mml:mo>∂</mml:mo>
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<mml:mi mathvariant="italic">u</mml:mi>
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</mml:mrow>
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</mml:mfenced>
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</mml:mfrac>
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</mml:mfenced>
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<mml:mo>×</mml:mo>
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<mml:mfenced open="" close="">
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<mml:mfrac>
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<mml:mfenced open="" close="">
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<mml:mrow>
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<mml:mo>∂</mml:mo>
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<mml:mi mathvariant="bold">p</mml:mi>
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</mml:mrow>
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</mml:mfenced>
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<mml:mfenced open="" close="">
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<mml:mrow>
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<mml:mo>∂</mml:mo>
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<mml:mi mathvariant="italic">v</mml:mi>
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</mml:mrow>
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</mml:mfenced>
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</mml:mfrac>
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</mml:mfenced>
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</mml:mrow>
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</mml:mrow>
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</mml:math></informalequation>
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</para>
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<para>
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Then the generated normal
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<inlineequation><mml:math>
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<!-- eqn: bold n:-->
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<mml:mi mathvariant="bold">n</mml:mi>
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</mml:math></inlineequation>
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is
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<inlineequation><mml:math>
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<!-- eqn: bold n = bold m over { || bold m || }:-->
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<mml:mrow>
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<mml:mi mathvariant="bold">n</mml:mi>
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<mml:mo>=</mml:mo>
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<mml:mfrac>
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<mml:mi mathvariant="bold">m</mml:mi>
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<mml:mfenced open="" close="">
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<mml:mfenced open="∥" close="∥">
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<mml:mi mathvariant="bold">m</mml:mi>
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</mml:mfenced>
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</mml:mfenced>
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</mml:mfrac>
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</mml:mrow>
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</mml:math></inlineequation>
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</para>
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<para>
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If automatic normal generation is disabled,
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the corresponding normal map <constant>GL_MAP2_NORMAL</constant>,
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if enabled,
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is used to produce a normal.
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If neither automatic normal generation nor a normal map is enabled,
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no normal is generated for
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<function>glEvalCoord2</function> commands.
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</para>
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</refsect1>
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<refsect1 id="associatedgets"><title>Associated Gets</title>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP1_VERTEX_3</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP1_VERTEX_4</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP1_INDEX</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP1_COLOR_4</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP1_NORMAL</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP1_TEXTURE_COORD_1</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP1_TEXTURE_COORD_2</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP1_TEXTURE_COORD_3</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP1_TEXTURE_COORD_4</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP2_VERTEX_3</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP2_VERTEX_4</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP2_INDEX</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP2_COLOR_4</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP2_NORMAL</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP2_TEXTURE_COORD_1</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP2_TEXTURE_COORD_2</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP2_TEXTURE_COORD_3</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_MAP2_TEXTURE_COORD_4</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_AUTO_NORMAL</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGetMap</refentrytitle></citerefentry>
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</para>
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</refsect1>
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<refsect1 id="seealso"><title>See Also</title>
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<para>
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<citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glColor</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glEvalMesh</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glEvalPoint</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glIndex</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glMap1</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glMap2</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glMapGrid</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glNormal</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexCoord</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glVertex</refentrytitle></citerefentry>
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</para>
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</refsect1>
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<refsect1 id="Copyright"><title>Copyright</title>
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<para>
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Copyright <trademark class="copyright"></trademark> 1991-2006
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Silicon Graphics, Inc. This document is licensed under the SGI
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Free Software B License. For details, see
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<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
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</para>
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</refsect1>
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</refentry>
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