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<?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="glViewport">
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<refmeta>
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2014-03-28 19:06:55 +00:00
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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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2009-03-08 00:46:58 +00:00
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<refentrytitle>glViewport</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glViewport</refname>
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<refpurpose>set the viewport</refpurpose>
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</refnamediv>
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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>glViewport</function></funcdef>
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<paramdef>GLint <parameter>x</parameter></paramdef>
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<paramdef>GLint <parameter>y</parameter></paramdef>
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<paramdef>GLsizei <parameter>width</parameter></paramdef>
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<paramdef>GLsizei <parameter>height</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<!-- eqn: ignoring delim $$ -->
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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>x</parameter></term>
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<term><parameter>y</parameter></term>
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<listitem>
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<para>
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Specify the lower left corner of the viewport rectangle,
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in pixels. The initial value is (0,0).
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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>width</parameter></term>
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<term><parameter>height</parameter></term>
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<listitem>
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<para>
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Specify the width and height
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of the viewport.
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When a GL context is first attached to a window,
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<parameter>width</parameter> and <parameter>height</parameter> are set to the dimensions of that
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window.
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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>glViewport</function> specifies the affine transformation of
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<inlineequation><mml:math><mml:mi mathvariant="italic">x</mml:mi></mml:math></inlineequation>
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and
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<inlineequation><mml:math><mml:mi mathvariant="italic">y</mml:mi></mml:math></inlineequation>
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from
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normalized device coordinates to window coordinates.
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Let
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<inlineequation><mml:math>
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<!-- eqn: (x sub nd, y sub nd):-->
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<mml:mfenced open="(" close=")">
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<mml:msub><mml:mi mathvariant="italic">x</mml:mi>
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<mml:mi mathvariant="italic">nd</mml:mi>
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</mml:msub>
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<mml:msub><mml:mi mathvariant="italic">y</mml:mi>
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<mml:mi mathvariant="italic">nd</mml:mi>
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</mml:msub>
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</mml:mfenced>
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</mml:math></inlineequation>
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be normalized device coordinates.
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Then the window coordinates
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<inlineequation><mml:math>
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<!-- eqn: (x sub w, y sub w):-->
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<mml:mfenced open="(" close=")">
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<mml:msub><mml:mi mathvariant="italic">x</mml:mi>
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<mml:mi mathvariant="italic">w</mml:mi>
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</mml:msub>
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<mml:msub><mml:mi mathvariant="italic">y</mml:mi>
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<mml:mi mathvariant="italic">w</mml:mi>
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</mml:msub>
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</mml:mfenced>
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</mml:math></inlineequation>
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are computed as follows:
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</para>
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<para>
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<informalequation><mml:math>
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<!-- eqn: x sub w = ( x sub nd + 1 ) left ( width over 2 right ) + x:-->
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<mml:mrow>
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<mml:msub><mml:mi mathvariant="italic">x</mml:mi>
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<mml:mi mathvariant="italic">w</mml:mi>
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</mml:msub>
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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:mrow>
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<mml:msub><mml:mi mathvariant="italic">x</mml:mi>
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<mml:mi mathvariant="italic">nd</mml:mi>
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</mml:msub>
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<mml:mo>+</mml:mo>
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<mml:mn>1</mml:mn>
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</mml:mrow>
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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:mi mathvariant="italic">width</mml:mi>
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<mml:mn>2</mml:mn>
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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:mi mathvariant="italic">x</mml:mi>
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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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<informalequation><mml:math>
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<!-- eqn: y sub w = ( y sub nd + 1 ) left ( height over 2 right ) + y:-->
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<mml:mrow>
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<mml:msub><mml:mi mathvariant="italic">y</mml:mi>
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<mml:mi mathvariant="italic">w</mml:mi>
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</mml:msub>
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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:mrow>
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<mml:msub><mml:mi mathvariant="italic">y</mml:mi>
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<mml:mi mathvariant="italic">nd</mml:mi>
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</mml:msub>
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<mml:mo>+</mml:mo>
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<mml:mn>1</mml:mn>
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</mml:mrow>
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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:mi mathvariant="italic">height</mml:mi>
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<mml:mn>2</mml:mn>
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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:mi mathvariant="italic">y</mml:mi>
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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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Viewport width and height are silently clamped
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to a range that depends on the implementation.
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To query this range, call <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument
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<constant>GL_MAX_VIEWPORT_DIMS</constant>.
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</para>
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</refsect1>
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<refsect1 id="errors"><title>Errors</title>
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<para>
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<constant>GL_INVALID_VALUE</constant> is generated if either <parameter>width</parameter> or <parameter>height</parameter> is negative.
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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>glGet</refentrytitle></citerefentry> with argument <constant>GL_VIEWPORT</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_MAX_VIEWPORT_DIMS</constant>
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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>glDepthRangef</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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