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197 lines
7.9 KiB
XML
197 lines
7.9 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="glDrawBuffers">
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<refmeta>
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<refentrytitle>glDrawBuffers</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glDrawBuffers</refname>
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<refpurpose>Specifies a list of color buffers to be drawn into</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>glDrawBuffers</function></funcdef>
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<paramdef>GLsizei <parameter>n</parameter></paramdef>
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<paramdef>const GLenum *<parameter>bufs</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>n</parameter></term>
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<listitem>
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<para>Specifies the number of buffers in
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<parameter>bufs</parameter>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>bufs</parameter></term>
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<listitem>
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<para>Points to an array of symbolic constants
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specifying the buffers into which fragment colors or
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data values will be written.</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><function>glDrawBuffers</function> defines an array of
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buffers into which fragment color values or fragment data will
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be written. If no fragment shader is active, rendering
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operations will generate only one fragment color per fragment
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and it will be written into each of the buffers specified by
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<parameter>bufs</parameter>. If a fragment shader is active and
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it writes a value to the output variable
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<code>gl_FragColor</code>, then that value will be
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written into each of the buffers specified by
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<parameter>bufs</parameter>. If a fragment shader is active and
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it writes a value to one or more elements of the output array
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variable <code>gl_FragData[]</code>, then the value of
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<code>gl_FragData[0] </code> will be written into the
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first buffer specified by <parameter>bufs</parameter>, the value
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of <code>gl_FragData[1] </code> will be written into the
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second buffer specified by <parameter>bufs</parameter>, and so
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on up to <code>gl_FragData[n-1]</code>. The draw buffer
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used for <code>gl_FragData[n]</code> and beyond is
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implicitly set to be <constant>GL_NONE</constant>.</para>
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<para>The symbolic constants contained in
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<parameter>bufs</parameter> may be any of the following:</para>
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<variablelist>
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<varlistentry>
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<term><constant>GL_NONE</constant></term>
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<listitem>
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<para>The fragment color/data value is not written into
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any color buffer.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_FRONT_LEFT</constant></term>
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<listitem>
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<para>The fragment color/data value is written into the
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front left color buffer.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_FRONT_RIGHT</constant></term>
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<listitem>
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<para>The fragment color/data value is written into the
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front right color buffer.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_BACK_LEFT</constant></term>
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<listitem>
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<para>The fragment color/data value is written into the
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back left color buffer.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_BACK_RIGHT</constant></term>
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<listitem>
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<para>The fragment color/data value is written into the
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back right color buffer.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_AUXi</constant></term>
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<listitem>
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<para>The fragment color/data value is written into
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auxiliary buffer <code>i</code>.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>Except for <constant>GL_NONE</constant>, the preceding
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symbolic constants may not appear more than once in
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<parameter>bufs</parameter>. The maximum number of draw buffers
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supported is implementation dependent and can be queried by
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calling
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
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with the argument <constant>GL_MAX_DRAW_BUFFERS</constant>. The
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number of auxiliary buffers can be queried by calling
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
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with the argument <constant>GL_AUX_BUFFERS</constant>.</para>
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</refsect1>
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<refsect1 id="notes"><title>Notes</title>
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<para><function>glDrawBuffers</function> is available only if
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the GL version is 2.0 or greater.</para>
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<para>It is always the case that <constant>GL_AUXi</constant> =
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<constant>GL_AUX0</constant> + <code>i</code>.</para>
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<para>The symbolic constants <constant>GL_FRONT</constant>,
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<constant>GL_BACK</constant>, <constant>GL_LEFT</constant>,
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<constant>GL_RIGHT</constant>, and
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<constant>GL_FRONT_AND_BACK</constant> are not allowed in the
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<parameter>bufs</parameter> array since they may refer to
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multiple buffers.</para>
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<para>If a fragment shader writes to neither
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<code>gl_FragColor</code> nor
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<code>gl_FragData</code>, the values of the fragment
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colors following shader execution are undefined. For each
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fragment generated in this situation, a different value may be
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written into each of the buffers specified by
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<parameter>bufs</parameter>.</para>
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</refsect1>
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<refsect1 id="errors"><title>Errors</title>
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<para><constant>GL_INVALID_ENUM</constant> is generated if one of the
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values in <parameter>bufs</parameter> is not an accepted
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value.</para>
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<para><constant>GL_INVALID_ENUM</constant> is generated if
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<parameter>n</parameter> is less than 0.</para>
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<para><constant>GL_INVALID_OPERATION</constant> is generated if a
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symbolic constant other than <constant>GL_NONE</constant>
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appears more than once in <parameter>bufs</parameter>.</para>
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<para><constant>GL_INVALID_OPERATION</constant> is generated if any of
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the entries in <parameter>bufs</parameter> (other than
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<constant>GL_NONE</constant> ) indicates a color buffer that
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does not exist in the current GL context.</para>
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<para><constant>GL_INVALID_VALUE</constant> is generated if
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<parameter>n</parameter> is greater than
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<constant>GL_MAX_DRAW_BUFFERS</constant>.</para>
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<para><constant>GL_INVALID_OPERATION</constant> is generated if
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<function>glDrawBuffers</function> is executed between the
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execution of
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<citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
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and the corresponding execution of
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<citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.</para>
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</refsect1>
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<refsect1 id="associatedgets"><title>Associated Gets</title>
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<para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
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with argument <constant>GL_MAX_DRAW_BUFFERS</constant></para>
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<para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
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with argument <constant>GL_DRAW_BUFFERSi</constant> where
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<code>i</code> indicates the number of the draw buffer
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whose value is to be queried</para>
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</refsect1>
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<refsect1 id="seealso"><title>See Also</title>
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<para> <citerefentry><refentrytitle>glBlendFunc</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glColorMask</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glDrawBuffers</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glIndexMask</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glLogicOp</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glReadBuffer</refentrytitle></citerefentry></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> 2003-2005 3Dlabs Inc. Ltd.
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This material may be distributed subject to the terms and conditions set forth in
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the Open Publication License, v 1.0, 8 June 1999.
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<ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
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</para>
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</refsect1>
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</refentry>
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