mirror of
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221 lines
9.6 KiB
XML
221 lines
9.6 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="glProvokingVertex">
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<refmeta>
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<refmetainfo>
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<copyright>
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<year>2010</year>
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<holder>Khronos Group</holder>
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</copyright>
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</refmetainfo>
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<refentrytitle>glProvokingVertex</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glProvokingVertex</refname>
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<refpurpose>specifiy the vertex to be used as the source of data for flat shaded varyings</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>glProvokingVertex</function></funcdef>
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<paramdef>GLenum <parameter>provokeMode</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>provokeMode</parameter></term>
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<listitem>
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<para>
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Specifies the vertex to be used as the source of data for flat shaded varyings.
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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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<emphasis>Flatshading</emphasis> a vertex shader varying output means to assign all vetices of the primitive the same value
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for that output. The vertex from which these values is derived is known as the <emphasis>provoking vertex</emphasis> and
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<function>glProvokingVertex</function> specifies which vertex is to be used as the source of data for flat shaded varyings.
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</para>
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<para>
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<parameter>provokeMode</parameter> must be either <constant>GL_FIRST_VERTEX_CONVENTION</constant> or
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<constant>GL_LAST_VERTEX_CONVENTION</constant>, and controls the selection of the vertex whose values are assigned to flatshaded
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varying outputs. The interpretation of these values for the supported primitive types is:
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<informaltable frame="topbot">
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<tgroup cols="3" align="left">
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<colspec colwidth="1.1*" />
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<colspec colwidth="1*" />
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<colspec colwidth="1*" />
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<thead>
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<row>
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<entry rowsep="1" align="left"><emphasis role="bold">
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Primitive Type of Polygon <emphasis>i</emphasis>
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</emphasis></entry>
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<entry rowsep="1" align="left"><emphasis role="bold">
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First Vertex Convention
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</emphasis></entry>
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<entry rowsep="1" align="left"><emphasis role="bold">
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Last Vertex Convention
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</emphasis></entry>
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</row>
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<row>
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<entry>
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point
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</entry>
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<entry>
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<emphasis>i</emphasis>
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</entry>
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<entry>
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<emphasis>i</emphasis>
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</entry>
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</row>
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<row>
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<entry>
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independent line
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</entry>
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<entry>
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2<emphasis>i</emphasis> - 1
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</entry>
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<entry>
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2<emphasis>i</emphasis>
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</entry>
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</row>
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<row>
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<entry>
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line loop
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</entry>
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<entry>
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<emphasis>i</emphasis>
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</entry>
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<entry>
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<para>
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<emphasis>i</emphasis> + 1, if <emphasis>i</emphasis> < <emphasis>n</emphasis>
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</para>
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<para>
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1, if <emphasis>i</emphasis> = <emphasis>n</emphasis>
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</para>
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</entry>
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</row>
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<row>
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<entry>
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line strip
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</entry>
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<entry>
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<emphasis>i</emphasis>
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</entry>
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<entry>
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<emphasis>i</emphasis> + 1
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</entry>
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</row>
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<row>
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<entry>
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independent triangle
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</entry>
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<entry>
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3<emphasis>i</emphasis> - 2
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</entry>
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<entry>
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3<emphasis>i</emphasis>
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</entry>
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</row>
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<row>
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<entry>
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triangle strip
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</entry>
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<entry>
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<emphasis>i</emphasis>
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</entry>
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<entry>
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<emphasis>i</emphasis> + 2
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</entry>
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</row>
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<row>
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<entry>
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triangle fan
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</entry>
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<entry>
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<emphasis>i</emphasis> + 1
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</entry>
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<entry>
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<emphasis>i</emphasis> + 2
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</entry>
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</row>
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<row>
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<entry>
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line adjacency
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</entry>
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<entry>
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4<emphasis>i</emphasis> - 2
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</entry>
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<entry>
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4<emphasis>i</emphasis> - 1
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</entry>
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</row>
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<row>
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<entry>
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line strip adjacency
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</entry>
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<entry>
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<emphasis>i</emphasis> + 1
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</entry>
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<entry>
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<emphasis>i</emphasis> + 2
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</entry>
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</row>
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<row>
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<entry>
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triangle adjacency
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</entry>
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<entry>
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6<emphasis>i</emphasis> - 5
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</entry>
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<entry>
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6<emphasis>i</emphasis> - 1
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</entry>
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</row>
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<row>
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<entry>
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triangle strip adjacency
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</entry>
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<entry>
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2<emphasis>i</emphasis> - 1
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</entry>
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<entry>
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2<emphasis>i</emphasis> + 3
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</entry>
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</row>
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</thead>
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</tgroup>
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</informaltable>
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</para>
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<para>
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If a vertex or geometry shader is active, user-defined varying outputs may be flatshaded by using the
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<code>flat</code> qualifier when declaring the output.
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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>glProvokingVertex</function> is 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 id="errors"><title>Errors</title>
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<para>
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<constant>GL_INVALID_ENUM</constant> is generated if <parameter>provokeMode</parameter> is not an accepted value.
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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> 2010 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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<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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