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190 lines
8.9 KiB
XML
190 lines
8.9 KiB
XML
<!DOCTYPE refentry [ <!ENTITY % mathent SYSTEM "math.ent"> %mathent; ]>
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<!-- Converted by db4-upgrade version 1.1 -->
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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glDrawElementsInstancedBaseInstance">
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<info>
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<copyright>
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<year>2011-2013</year>
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<holder>Khronos Group</holder>
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</copyright>
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</info>
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<refmeta>
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<refentrytitle>glDrawElementsInstancedBaseInstance</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glDrawElementsInstancedBaseInstance</refname>
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<refpurpose>draw multiple instances of a set of elements with offset applied to instanced attributes</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>glDrawElementsInstancedBaseInstance</function></funcdef>
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<paramdef>GLenum <parameter>mode</parameter></paramdef>
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<paramdef>GLsizei <parameter>count</parameter></paramdef>
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<paramdef>GLenum <parameter>type</parameter></paramdef>
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<paramdef>const void * <parameter>indices</parameter></paramdef>
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<paramdef>GLsizei <parameter>primcount</parameter></paramdef>
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<paramdef>GLuitn <parameter>baseinstance</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1 xml:id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>mode</parameter></term>
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<listitem>
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<para>
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Specifies what kind of primitives to render.
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Symbolic constants
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<constant>GL_POINTS</constant>,
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<constant>GL_LINE_STRIP</constant>,
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<constant>GL_LINE_LOOP</constant>,
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<constant>GL_LINES</constant>,
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<constant>GL_LINE_STRIP_ADJACENCY</constant>,
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<constant>GL_LINES_ADJACENCY</constant>,
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<constant>GL_TRIANGLE_STRIP</constant>,
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<constant>GL_TRIANGLE_FAN</constant>,
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<constant>GL_TRIANGLES</constant>,
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<constant>GL_TRIANGLE_STRIP_ADJACENCY</constant>,
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<constant>GL_TRIANGLES_ADJACENCY</constant> and <constant>GL_PATCHES</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>count</parameter></term>
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<listitem>
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<para>
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Specifies the number of elements to be rendered.
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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>type</parameter></term>
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<listitem>
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<para>
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Specifies the type of the values in <parameter>indices</parameter>. Must be one of <constant>GL_UNSIGNED_BYTE</constant>,
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<constant>GL_UNSIGNED_SHORT</constant>, or <constant>GL_UNSIGNED_INT</constant>.
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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>indices</parameter></term>
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<listitem>
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<para>
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Specifies a pointer to the location where the indices are stored.
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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>primcount</parameter></term>
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<listitem>
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<para>
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Specifies the number of instances of the specified range of indices to be rendered.
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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>baseinstance</parameter></term>
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<listitem>
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<para>
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Specifies the base instance for use in fetching instanced vertex attributes.
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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 xml:id="description"><title>Description</title>
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<para>
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<function>glDrawElementsInstancedBaseInstance</function> behaves identically to <citerefentry><refentrytitle>glDrawElements</refentrytitle></citerefentry>
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except that <parameter>primcount</parameter> instances of the set of elements are executed and the value of the internal counter
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<parameter>instanceID</parameter> advances for each iteration. <parameter>instanceID</parameter> is an internal 32-bit integer counter
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that may be read by a vertex shader as <constant>gl_InstanceID</constant>.
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</para>
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<para>
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<function>glDrawElementsInstancedBaseInstance</function> has the same effect as:
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<programlisting> if (mode, count, or type is invalid )
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generate appropriate error
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else {
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for (int i = 0; i < primcount ; i++) {
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instanceID = i;
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glDrawElements(mode, count, type, indices);
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}
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instanceID = 0;
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}</programlisting>
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</para>
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<para>
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Specific vertex attributes may be classified as <emphasis>instanced</emphasis> through the use of
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<citerefentry><refentrytitle>glVertexAttribDivisor</refentrytitle></citerefentry>. Instanced vertex attributes
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supply per-instance vertex data to the vertex shader. The index of the vertex fetched from the enabled instanced vertex
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attribute arrays is calculated as
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<inlineequation>
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<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
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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:mrow>
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<mml:mi>gl</mml:mi>
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<mml:mo>_</mml:mo>
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<mml:mi>InstanceID</mml:mi>
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</mml:mrow>
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<mml:mi>divisor</mml:mi>
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</mml:mfrac>
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</mml:mfenced>
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<mml:mo lspace="2px" rspace="2px">+</mml:mo>
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<mml:mi>baseInstance</mml:mi>
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</mml:mrow>
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</mml:math>
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</inlineequation>. Note that
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<parameter>baseinstance</parameter> does not affect the
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shader-visible value of <constant>gl_InstanceID</constant>.
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</para>
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</refsect1>
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<refsect1 xml:id="notes"><title>Notes</title>
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<para>
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<function>glDrawElementsInstancedBaseInstance</function> is available only if the GL version is 4.2 or greater.
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</para>
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<para>
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<constant>GL_LINE_STRIP_ADJACENCY</constant>,
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<constant>GL_LINES_ADJACENCY</constant>,
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<constant>GL_TRIANGLE_STRIP_ADJACENCY</constant> and
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<constant>GL_TRIANGLES_ADJACENCY</constant>
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are available only if the GL version is 3.2 or greater.
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</para>
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</refsect1>
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<refsect1 xml:id="errors"><title>Errors</title>
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<para>
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<constant>GL_INVALID_ENUM</constant> is generated if <parameter>mode</parameter> is not one of <constant>GL_POINTS</constant>,
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<constant>GL_LINE_STRIP</constant>, <constant>GL_LINE_LOOP</constant>, <constant>GL_LINES</constant>,
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<constant>GL_TRIANGLE_STRIP</constant>, <constant>GL_TRIANGLE_FAN</constant>, or <constant>GL_TRIANGLES</constant>.
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</para>
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<para>
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<constant>GL_INVALID_VALUE</constant> is generated if <parameter>count</parameter> or <parameter>primcount</parameter> are negative.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if a geometry shader is active and <parameter>mode</parameter>
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is incompatible with the input primitive type of the geometry shader in the currently installed program object.
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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 an
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enabled array and the buffer object's data store is currently mapped.
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</para>
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</refsect1>
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<refsect1 xml:id="seealso"><title>See Also</title>
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<para>
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<citerefentry><refentrytitle>glDrawElements</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glDrawArraysInstanced</refentrytitle></citerefentry>
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</para>
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</refsect1>
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<refsect1 xml:id="Copyright"><title>Copyright</title>
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<para>
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Copyright <trademark class="copyright"/> 2011-2013 Khronos Group.
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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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<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://opencontent.org/openpub/">http://opencontent.org/openpub/</link>.
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</para>
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</refsect1>
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</refentry>
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