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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glDrawElementsIndirect">
    <info>
        <copyright>
            <year>2010-2015</year>
            <holder>Khronos Group.</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>glDrawElementsIndirect</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glDrawElementsIndirect</refname>
        <refpurpose>render indexed primitives from array data, taking parameters from memory</refpurpose>
    </refnamediv>
    <refsynopsisdiv>
        <title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glDrawElementsIndirect</function></funcdef>
                <paramdef>GLenum <parameter>mode</parameter></paramdef>
                <paramdef>GLenum <parameter>type</parameter></paramdef>
                <paramdef>const void *<parameter>indirect</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <!-- eqn: ignoring delim $$ -->
    <refsect1 xml: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>type</parameter></term>
            <listitem>
                <para>
                    Specifies the type of data in the buffer bound to the <constant>GL_ELEMENT_ARRAY_BUFFER</constant> binding.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>indirect</parameter></term>
            <listitem>
                <para>
                    Specifies the address of a structure containing the draw parameters.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 xml:id="description"><title>Description</title>
        <para>
            <function>glDrawElementsIndirect</function> specifies multiple indexed geometric primitives
            with very few subroutine calls. <function>glDrawElementsIndirect</function> behaves
            similarly to <citerefentry><refentrytitle>glDrawElementsInstanced</refentrytitle></citerefentry>,
            except that the parameters to <citerefentry><refentrytitle>glDrawElementsInstanced</refentrytitle></citerefentry>
            are stored in memory at the address given by <parameter>indirect</parameter> and 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.It also supports the addition of 
			a value baseVertex to each index.
        </para>
        <para>
            The parameters addressed by <parameter>indirect</parameter> are packed into a structure
            that takes the form (in C):
        </para>
            <programlisting>    typedef  struct {
        uint  count;
        uint  instanceCount;
        uint  firstIndex;
        int   baseVertex;
        uint  reservedMustBeZero;
    } DrawElementsIndirectCommand;</programlisting>
        <para>
            <function>glDrawElementsIndirect</function> is equivalent to:
        </para>
        <para>
<programlisting>    void glDrawElementsIndirect(GLenum mode, GLenum type, const void * indirect)
    {
        const DrawElementsIndirectCommand *cmd  = (const DrawElementsIndirectCommand *)indirect;
        glDrawElementsInstancedBaseVertex(mode,
                                          cmd-&gt;count,
                                          type,
                                          cmd-&gt;firstIndex * size-of-type,
                                          cmd-&gt;instanceCount,
                                          cmd-&gt;baseVertex);
    }</programlisting>
        </para>
        <para>
            If a buffer is bound to the <constant>GL_DRAW_INDIRECT_BUFFER</constant> binding at the time
            of a call to <function>glDrawElementsIndirect</function>, <parameter>indirect</parameter>
            is interpreted as an offset, in basic machine units, into that buffer and the parameter
            data is read from the buffer rather than from client memory.
        </para>
        <para>
            Note that indices stored in client memory are not supported. If no buffer is bound to the
            <constant>GL_ELEMENT_ARRAY_BUFFER</constant> binding, an error will be generated.
        </para>
        <para>
            The results of the operation are undefined if the <code>reservedMustBeZero</code> member
            of the parameter structure is non-zero. However, no error is generated in this case.
        </para>
        <para>
            Vertex attributes that are modified by <function>glDrawElementsIndirect</function> have an
            unspecified value after <function>glDrawElementsIndirect</function> returns. Attributes that aren't
            modified remain well defined.
        </para>
    </refsect1>
    <refsect1 xml:id="notes"><title>Notes</title>
        <para>
            <function>glDrawElementsInstancedBaseVertex</function> isn't actually present in OpenGL ES, but is used to describe this functionality.
        </para>
        <para>
            <constant>GL_LINE_STRIP_ADJACENCY</constant>,
            <constant>GL_LINES_ADJACENCY</constant>,
            <constant>GL_TRIANGLE_STRIP_ADJACENCY</constant>,
            <constant>GL_TRIANGLES_ADJACENCY</constant> and
            <constant>GL_PATCHES</constant>
            are available only if the GL ES 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>mode</parameter> is not an accepted value.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if no buffer is bound to the <constant>GL_ELEMENT_ARRAY_BUFFER</constant>
            binding, or if such a buffer's data store is currently mapped.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to an
            enabled array or to the <constant>GL_DRAW_INDIRECT_BUFFER</constant> binding and the buffer object's data store is currently mapped.
        </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>
    </refsect1>
    <refsect1 xml:id="versions">
        <title>API Version Support</title>
        <informaltable>
            <tgroup cols="5" align="left">
                <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
                <tbody>
                    <row>
                        <entry><function>glDrawElementsIndirect</function></entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es31']/*)"/>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glDrawArrays</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glDrawArraysInstanced</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glDrawArraysIndirect</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glDrawElements</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glDrawRangeElements</refentrytitle></citerefentry>,
        </para>
    </refsect1>
    <refsect1 xml:id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"/> 2010-2015 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>
