176 lines
10 KiB
XML
176 lines
10 KiB
XML
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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="glGetCompressedTexImage">
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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>glGetCompressedTexImage</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glGetCompressedTexImage</refname>
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<refpurpose>return a compressed texture image</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>glGetCompressedTexImage</function></funcdef>
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<paramdef>GLenum <parameter>target</parameter></paramdef>
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<paramdef>GLint <parameter>lod</parameter></paramdef>
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<paramdef>GLvoid * <parameter>img</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>target</parameter></term>
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<listitem>
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<para>
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Specifies which texture is to be obtained.
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<constant>GL_TEXTURE_1D</constant>, <constant>GL_TEXTURE_2D</constant>, and <constant>GL_TEXTURE_3D</constant>
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<constant>GL_TEXTURE_CUBE_MAP_POSITIVE_X</constant>,
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<constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_X</constant>,
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<constant>GL_TEXTURE_CUBE_MAP_POSITIVE_Y</constant>,
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<constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_Y</constant>,
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<constant>GL_TEXTURE_CUBE_MAP_POSITIVE_Z</constant>, and
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<constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_Z</constant>
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are accepted.
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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>lod</parameter></term>
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<listitem>
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<para>
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Specifies the level-of-detail number of the desired image.
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Level 0 is the base image level.
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Level
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<inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>
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is the
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<inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>th
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mipmap reduction image.
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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>img</parameter></term>
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<listitem>
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<para>
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Returns the compressed texture image.
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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>glGetCompressedTexImage</function> returns the compressed texture image associated with <parameter>target</parameter> and <parameter>lod</parameter>
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into <parameter>img</parameter>. <parameter>img</parameter> should be an array of
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<constant>GL_TEXTURE_COMPRESSED_IMAGE_SIZE</constant> bytes.
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<parameter>target</parameter> specifies whether the desired texture image was one specified by
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<citerefentry><refentrytitle>glTexImage1D</refentrytitle></citerefentry> (<constant>GL_TEXTURE_1D</constant>),
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<citerefentry><refentrytitle>glTexImage2D</refentrytitle></citerefentry> (<constant>GL_TEXTURE_2D</constant> or any of <constant>GL_TEXTURE_CUBE_MAP_*</constant>), or
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<citerefentry><refentrytitle>glTexImage3D</refentrytitle></citerefentry> (<constant>GL_TEXTURE_3D</constant>).
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<parameter>lod</parameter> specifies the level-of-detail number of the desired image.
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</para>
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<para>
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If a non-zero named buffer object is bound to the <constant>GL_PIXEL_PACK_BUFFER</constant> target
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(see <citerefentry><refentrytitle>glBindBuffer</refentrytitle></citerefentry>) while a texture image is
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requested, <parameter>img</parameter> is treated as a byte offset into the buffer object's data store.
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</para>
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<para>
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To minimize errors, first verify that the texture is compressed by calling
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<citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> with argument <constant>GL_TEXTURE_COMPRESSED</constant>. If
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the texture is compressed, then determine the amount of memory required to
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store the compressed texture by calling <citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> with
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argument <constant>GL_TEXTURE_COMPRESSED_IMAGE_SIZE</constant>. Finally, retrieve the
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internal format of the texture by calling <citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> with
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argument <constant>GL_TEXTURE_INTERNAL_FORMAT</constant>.
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To store the texture for later use, associate the internal format and size
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with the retrieved texture image. These data can be used by the respective
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texture or subtexture loading routine used for loading <parameter>target</parameter> textures.
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</para>
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</refsect1>
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<refsect1 id="notes"><title>Notes</title>
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<para>
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<function>glGetCompressedTexImage</function> is available only if the GL version is 1.3 or greater.
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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 <parameter>lod</parameter> is less than zero or greater
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than the maximum number of LODs permitted by the implementation.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <function>glGetCompressedTexImage</function> is used to retrieve a
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texture that is in an uncompressed internal format.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
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<constant>GL_PIXEL_PACK_BUFFER</constant> target and the buffer object's data store is currently mapped.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
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<constant>GL_PIXEL_PACK_BUFFER</constant> target and the data would be packed to the buffer
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object such that the memory writes required would exceed the data store size.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <function>glGetCompressedTexImage</function>
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is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
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and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.
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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>glGetTexLevelParameter</refentrytitle></citerefentry> with argument <constant>GL_TEXTURE_COMPRESSED</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> with argument <constant>GL_TEXTURE_COMPRESSED_IMAGE_SIZE</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> with argument <constant>GL_TEXTURE_INTERNAL_FORMAT</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_PIXEL_PACK_BUFFER_BINDING</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>glActiveTexture</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glCompressedTexImage1D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glCompressedTexImage2D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glCompressedTexImage3D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glCompressedTexSubImage1D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glCompressedTexSubImage2D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glCompressedTexSubImage3D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glDrawPixels</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glReadPixels</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexEnv</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexGen</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexImage1D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexImage2D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexImage3D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexParameter</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexSubImage1D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexSubImage2D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexSubImage3D</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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