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<!DOCTYPE refentry [ <!ENTITY % mathent SYSTEM "math.ent"> %mathent; ]>
<!-- Converted by db4-upgrade version 1.1 -->
<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glProvokingVertex">
<info>
<copyright>
<year>2010-2014</year>
<holder>Khronos Group</holder>
</copyright>
</info>
<refmeta>
<refentrytitle>glProvokingVertex</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>glProvokingVertex</refname>
<refpurpose>specifiy the vertex to be used as the source of data for flat shaded varyings</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glProvokingVertex</function></funcdef>
<paramdef>GLenum <parameter>provokeMode</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 xml:id="parameters"><title>Parameters</title>
<variablelist>
<varlistentry>
<term><parameter>provokeMode</parameter></term>
<listitem>
<para>
Specifies the vertex to be used as the source of data for flat shaded varyings.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 xml:id="description"><title>Description</title>
<para>
<emphasis>Flatshading</emphasis> a vertex shader varying output means to assign all vetices of the primitive the same value
for that output. The vertex from which these values is derived is known as the <emphasis>provoking vertex</emphasis> and
<function>glProvokingVertex</function> specifies which vertex is to be used as the source of data for flat shaded varyings.
</para>
<para>
<parameter>provokeMode</parameter> must be either <constant>GL_FIRST_VERTEX_CONVENTION</constant> or
<constant>GL_LAST_VERTEX_CONVENTION</constant>, and controls the selection of the vertex whose values are assigned to flatshaded
varying outputs. The interpretation of these values for the supported primitive types is:
<informaltable>
<tgroup cols="3" align="left">
<colspec colwidth="1.1*"/>
<colspec colwidth="1*"/>
<colspec colwidth="1*"/>
<thead>
<row>
<entry>
<emphasis role="bold"> Primitive Type of Polygon <emphasis>i</emphasis> </emphasis>
</entry>
<entry><emphasis role="bold"> First Vertex Convention </emphasis>
</entry>
<entry>
<emphasis role="bold"> Last Vertex Convention </emphasis>
</entry>
</row>
</thead>
<tbody>
<row>
<entry>
point
</entry>
<entry>
<emphasis>i</emphasis>
</entry>
<entry>
<emphasis>i</emphasis>
</entry>
</row>
<row>
<entry>
independent line
</entry>
<entry>
2<emphasis>i</emphasis> - 1
</entry>
<entry>
2<emphasis>i</emphasis>
</entry>
</row>
<row>
<entry>
line loop
</entry>
<entry>
<emphasis>i</emphasis>
</entry>
<entry>
<para>
<emphasis>i</emphasis> + 1, if <emphasis>i</emphasis> < <emphasis>n</emphasis>
</para>
<para>
1, if <emphasis>i</emphasis> = <emphasis>n</emphasis>
</para>
</entry>
</row>
<row>
<entry>
line strip
</entry>
<entry>
<emphasis>i</emphasis>
</entry>
<entry>
<emphasis>i</emphasis> + 1
</entry>
</row>
<row>
<entry>
independent triangle
</entry>
<entry>
3<emphasis>i</emphasis> - 2
</entry>
<entry>
3<emphasis>i</emphasis>
</entry>
</row>
<row>
<entry>
triangle strip
</entry>
<entry>
<emphasis>i</emphasis>
</entry>
<entry>
<emphasis>i</emphasis> + 2
</entry>
</row>
<row>
<entry>
triangle fan
</entry>
<entry>
<emphasis>i</emphasis> + 1
</entry>
<entry>
<emphasis>i</emphasis> + 2
</entry>
</row>
<row>
<entry>
line adjacency
</entry>
<entry>
4<emphasis>i</emphasis> - 2
</entry>
<entry>
4<emphasis>i</emphasis> - 1
</entry>
</row>
<row>
<entry>
line strip adjacency
</entry>
<entry>
<emphasis>i</emphasis> + 1
</entry>
<entry>
<emphasis>i</emphasis> + 2
</entry>
</row>
<row>
<entry>
triangle adjacency
</entry>
<entry>
6<emphasis>i</emphasis> - 5
</entry>
<entry>
6<emphasis>i</emphasis> - 1
</entry>
</row>
<row>
<entry>
triangle strip adjacency
</entry>
<entry>
2<emphasis>i</emphasis> - 1
</entry>
<entry>
2<emphasis>i</emphasis> + 3
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
<para>
If a vertex or geometry shader is active, user-defined varying outputs may be flatshaded by using the
<code>flat</code> qualifier when declaring the output.
</para>
</refsect1>
<refsect1 xml:id="notes"><title>Notes</title>
<para>
<function>glProvokingVertex</function> is available only if the GL version is 3.2 or greater.
</para>
</refsect1>
<refsect1 xml:id="errors"><title>Errors</title>
<para>
<constant>GL_INVALID_ENUM</constant> is generated if <parameter>provokeMode</parameter> is not an accepted value.
</para>
</refsect1>
<refsect1 xml:id="versions"><title>Version Support</title>
<informaltable>
<tgroup cols="13" align="left">
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
<tbody>
<row>
<entry><function>glProvokingVertex</function></entry>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='32']/*)"/>
</row>
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 xml:id="seealso"><title>See Also</title>
<!-- TBD -->
</refsect1>
<refsect1 xml:id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"/> 2010-2014 Khronos Group.
This material may be distributed subject to the terms and conditions set forth in
the Open Publication License, v 1.0, 8 June 1999.
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://opencontent.org/openpub/">http://opencontent.org/openpub/</link>.
</para>
</refsect1>
</refentry>
|
