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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="glDrawElementsInstancedBaseVertexBaseInstance">
<refentryinfo>
<copyright>
<year>2011-2013</year>
<holder>Khronos Group</holder>
</copyright>
</refentryinfo>
<refmeta>
<refentrytitle>glDrawElementsInstancedBaseVertexBaseInstance</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>glDrawElementsInstancedBaseVertexBaseInstance</refname>
<refpurpose>render multiple instances of a set of primitives from array data with a per-element offset</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glDrawElementsInstancedBaseVertexBaseInstance</function></funcdef>
<paramdef>GLenum <parameter>mode</parameter></paramdef>
<paramdef>GLsizei <parameter>count</parameter></paramdef>
<paramdef>GLenum <parameter>type</parameter></paramdef>
<paramdef>GLvoid *<parameter>indices</parameter></paramdef>
<paramdef>GLsizei <parameter>primcount</parameter></paramdef>
<paramdef>GLint <parameter>basevertex</parameter></paramdef>
<paramdef>GLuint <parameter>baseinstance</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_TRIANGLE_STRIP</constant>, <constant>GL_TRIANGLE_FAN</constant>,
<constant>GL_TRIANGLES</constant>, <constant>GL_LINES_ADJACENCY</constant>, <constant>GL_LINE_STRIP_ADJACENCY</constant>,
<constant>GL_TRIANGLES_ADJACENCY</constant>, <constant>GL_TRIANGLE_STRIP_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 indices. 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 indexed geometry that should be drawn.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>basevertex</parameter></term>
<listitem>
<para>
Specifies a constant that should be added to each element of <parameter>indices</parameter>
when chosing elements from the enabled vertex arrays.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>baseinstance</parameter></term>
<listitem>
<para>
Specifies the base instance for use in fetching instanced vertex attributes.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="description"><title>Description</title>
<para>
<function>glDrawElementsInstancedBaseVertexBaseInstance</function> behaves identically to
<citerefentry><refentrytitle>glDrawElementsInstanced</refentrytitle></citerefentry> except that the <emphasis>i</emphasis>th element
transferred by the corresponding draw call will be taken from element <parameter>indices</parameter>[i] + <parameter>basevertex</parameter>
of each enabled array. If the resulting value is larger than the maximum value representable by <parameter>type</parameter>,
it is as if the calculation were upconverted to 32-bit unsigned integers (with wrapping on overflow conditions).
The operation is undefined if the sum would be negative. The <parameter>basevertex</parameter> has no effect on the
shader-visible value of <constant>gl_VertexID</constant>.
</para>
<para>
Specific vertex attributes may be classified as <emphasis>instanced</emphasis> through the use of
<citerefentry><refentrytitle>glVertexAttribDivisor</refentrytitle></citerefentry>. Instanced vertex attributes
supply per-instance vertex data to the vertex shader. The index of the vertex fetched from the enabled instanced vertex
attribute arrays is calculated as
<inlineequation>
<mml:math>
<mml:mrow>
<mml:mfenced open = '⌊' close = '⌋'>
<mml:mfrac>
<mml:mrow>
<mml:mi>gl</mml:mi>
<mml:mo>_</mml:mo>
<mml:mi>InstanceID</mml:mi>
</mml:mrow>
<mml:mi>divisor</mml:mi>
</mml:mfrac>
</mml:mfenced>
<mml:mo lspace='2px' rspace='2px'>+</mml:mo>
<mml:mi>baseInstance</mml:mi>
</mml:mrow>
</mml:math>
</inlineequation>. Note that <parameter>baseinstance</parameter>
does not affect the shader-visible value of
<constant>gl_InstanceID</constant>.
</para>
</refsect1>
<refsect1 id="notes"><title>Notes</title>
<para>
<function>glDrawElementsInstancedBaseVertex</function> is only supported 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 an accepted value.
</para>
<para>
<constant>GL_INVALID_VALUE</constant> is generated if <parameter>count</parameter> or <parameter>primcount</parameter> is 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 or the element 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>glDrawRangeElements</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glDrawRangeElementsBaseVertex</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glDrawElementsInstanced</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glDrawElementsInstancedBaseVertex</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"></trademark> 2011-2013 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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