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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
<refentry id="glDrawElementsInstanced">
<refentryinfo>
<copyright>
<year>2010-2013</year>
<holder>Khronos Group</holder>
</copyright>
</refentryinfo>
<refmeta>
<refentrytitle>glDrawElementsInstanced</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>glDrawElementsInstanced</refname>
<refpurpose>draw multiple instances of a set of elements</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glDrawElementsInstanced</function></funcdef>
<paramdef>GLenum <parameter>mode</parameter></paramdef>
<paramdef>GLsizei <parameter>count</parameter></paramdef>
<paramdef>GLenum <parameter>type</parameter></paramdef>
<paramdef>const void * <parameter>indices</parameter></paramdef>
<paramdef>GLsizei <parameter>primcount</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 id="parameters"><title>Parameters</title>
<variablelist>
<varlistentry>
<term><parameter>mode</parameter></term>
<listitem>
<para>
Specifies what kind of primitives to render.
Symbolic constants
<constant>GL_POINTS</constant>,
<constant>GL_LINE_STRIP</constant>,
<constant>GL_LINE_LOOP</constant>,
<constant>GL_LINES</constant>,
<constant>GL_LINE_STRIP_ADJACENCY</constant>,
<constant>GL_LINES_ADJACENCY</constant>,
<constant>GL_TRIANGLE_STRIP</constant>,
<constant>GL_TRIANGLE_FAN</constant>,
<constant>GL_TRIANGLES</constant>,
<constant>GL_TRIANGLE_STRIP_ADJACENCY</constant>,
<constant>GL_TRIANGLES_ADJACENCY</constant> and <constant>GL_PATCHES</constant>
are accepted.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>count</parameter></term>
<listitem>
<para>
Specifies the number of elements to be rendered.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>type</parameter></term>
<listitem>
<para>
Specifies the type of the values in <parameter>indices</parameter>. Must be one of <constant>GL_UNSIGNED_BYTE</constant>,
<constant>GL_UNSIGNED_SHORT</constant>, or <constant>GL_UNSIGNED_INT</constant>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>indices</parameter></term>
<listitem>
<para>
Specifies a pointer to the location where the indices are stored.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>primcount</parameter></term>
<listitem>
<para>
Specifies the number of instances of the specified range of indices to be rendered.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="description"><title>Description</title>
<para>
<function>glDrawElementsInstanced</function> behaves identically to <citerefentry><refentrytitle>glDrawElements</refentrytitle></citerefentry>
except that <parameter>primcount</parameter> instances of the set of elements are executed and the value of the internal counter
<parameter>instanceID</parameter> advances for each iteration. <parameter>instanceID</parameter> is an internal 32-bit integer counter
that may be read by a vertex shader as <constant>gl_InstanceID</constant>.
</para>
<para>
<function>glDrawElementsInstanced</function> has the same effect as:
<programlisting> if (mode, count, or type is invalid )
generate appropriate error
else {
for (int i = 0; i < primcount ; i++) {
instanceID = i;
glDrawElements(mode, count, type, indices);
}
instanceID = 0;
}</programlisting>
</para>
</refsect1>
<refsect1 id="notes"><title>Notes</title>
<para>
<function>glDrawElementsInstanced</function> is available only if the GL version is 3.1 or greater.
</para>
<para>
<constant>GL_LINE_STRIP_ADJACENCY</constant>,
<constant>GL_LINES_ADJACENCY</constant>,
<constant>GL_TRIANGLE_STRIP_ADJACENCY</constant> and
<constant>GL_TRIANGLES_ADJACENCY</constant>
are available only if the GL version is 3.2 or greater.
</para>
</refsect1>
<refsect1 id="errors"><title>Errors</title>
<para>
<constant>GL_INVALID_ENUM</constant> is generated if <parameter>mode</parameter> is not one of <constant>GL_POINTS</constant>,
<constant>GL_LINE_STRIP</constant>, <constant>GL_LINE_LOOP</constant>, <constant>GL_LINES</constant>,
<constant>GL_TRIANGLE_STRIP</constant>, <constant>GL_TRIANGLE_FAN</constant>, or <constant>GL_TRIANGLES</constant>.
</para>
<para>
<constant>GL_INVALID_VALUE</constant> is generated if <parameter>count</parameter> or <parameter>primcount</parameter> are negative.
</para>
<para>
<constant>GL_INVALID_OPERATION</constant> is generated if a geometry shader is active and <parameter>mode</parameter>
is incompatible with the input primitive type of the geometry shader in the currently installed program object.
</para>
<para>
<constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to an
enabled array and the buffer object's data store is currently mapped.
</para>
</refsect1>
<refsect1 id="seealso"><title>See Also</title>
<para>
<citerefentry><refentrytitle>glDrawElements</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glDrawArraysInstanced</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"></trademark> 2010-2013 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.
<ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
</para>
</refsect1>
</refentry>
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