Opentk/Source/Bind/Specifications/Docs/glMultiDrawArraysIndirect.xml

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<refentry id="glMultiDrawArraysIndirect">
    <refentryinfo>
        <copyright>
            <year>2012-2013</year>
            <holder>Khronos Group.</holder>
        </copyright>
    </refentryinfo>
    <refmeta>
        <refentrytitle>glMultiDrawArraysIndirect</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glMultiDrawArraysIndirect</refname>
        <refpurpose>render multiple sets of primitives from array data, taking parameters from memory</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glMultiDrawArraysIndirect</function></funcdef>
                <paramdef>GLenum <parameter>mode</parameter></paramdef>
                <paramdef>const void *<parameter>indirect</parameter></paramdef>
                <paramdef>GLsizei <parameter>drawcount</parameter></paramdef>
                <paramdef>GLsizei <parameter>stride</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>indirect</parameter></term>
            <listitem>
                <para>
                    Specifies the address of an array of structures containing the draw parameters.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>drawcount</parameter></term>
            <listitem>
                <para>
                    Specifies the the number of elements in the array of draw parameter structures.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>stride</parameter></term>
            <listitem>
                <para>
                    Specifies the distance in basic machine units between elements of the draw parameter array.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
        <para>
            <function>glMultiDrawArraysIndirect</function> specifies multiple geometric primitives
            with very few subroutine calls. <function>glMultiDrawArraysIndirect</function> behaves
            similarly to a multitude of calls to <citerefentry><refentrytitle>glDrawArraysInstancedBaseInstance</refentrytitle></citerefentry>,
            execept that the parameters to each call to <citerefentry><refentrytitle>glDrawArraysInstancedBaseInstance</refentrytitle></citerefentry>
            are stored in an array in memory at the address given by <parameter>indirect</parameter>, separated
            by the stride, in basic machine units, specified by <parameter>stride</parameter>. If <parameter>stride</parameter>
            is zero, then the array is assumed to be tightly packed in memory.
        </para>
        <para>
            The parameters addressed by <parameter>indirect</parameter> are packed into an array of structures,
            each element of which takes the form (in C):
            <programlisting><![CDATA[    typedef  struct {
        uint  count;
        uint  instanceCount;
        uint  first;
        uint  baseInstance;
    } DrawArraysIndirectCommand;]]></programlisting>
        </para>
        <para>
            A single call to <function>glMultiDrawArraysIndirect</function> is equivalent, assuming no errors
            are generated to:
            <programlisting><![CDATA[    GLsizei n;
    for (n = 0; n < drawcount; n++)
    {
        const DrawArraysIndirectCommand  *cmd;
        if (stride != 0)
        {
            cmd = (const DrawArraysIndirectCommand  *)((uintptr)indirect + n * stride);
        }
        else
        {
            cmd = (const DrawArraysIndirectCommand  *)indirect + n;
        }

        glDrawArraysInstancedBaseInstance(mode,  cmd->first,  cmd->count,  cmd->instanceCount, cmd->baseInstance);
    }]]></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>glMultiDrawArraysIndirect</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>
            In contrast to <citerefentry><refentrytitle>glDrawArraysInstancedBaseInstance</refentrytitle></citerefentry>,
            the <code>first</code> member of the parameter structure is unsigned, and out-of-range indices
            do not generate an error.
        </para>
        <para>
            Vertex attributes that are modified by <function>glMultiDrawArraysIndirect</function> have an
            unspecified value after <function>glMultiDrawArraysIndirect</function> returns. Attributes that aren't
            modified remain well defined.
        </para>
    </refsect1>
    <refsect1 id="notes"><title>Notes</title>
        <para>
            The <parameter>baseInstance</parameter> member of the <parameter>DrawArraysIndirectCommand</parameter>
            structure is defined only if the GL version is 4.2 or greater. For versions of the GL less than 4.2,
            this parameter is present but is reserved and should be set to zero. On earlier versions of the GL,
            behavior is undefined if it is non-zero.
        </para>
        <para>
            <function>glMultiDrawArraysIndirect</function> is available only if the GL version is 4.3 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>stride</parameter> is not a multiple
            of four.
        </para>
        <para>
            <constant>GL_INVALID_VALUE</constant> is generated if <parameter>drawcount</parameter> is negative.
        </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>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>mode</parameter> is <constant>GL_PATCHES</constant>
            and no tessellation control shader is active.
        </para>
    </refsect1>
    <refsect1 id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glDrawArrays</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glDrawArraysInstanced</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glDrawElements</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glDrawRangeElements</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glDrawArraysIndirect</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glMultiDrawElementsIndirect</refentrytitle></citerefentry>
        </para>
    </refsect1>
    <refsect1 id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"></trademark> 2012-2013 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>