<!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="glBeginTransformFeedback">
    <info>
        <copyright>
            <year>2010-2014</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>glBeginTransformFeedback</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glBeginTransformFeedback</refname>
        <refpurpose>start transform feedback operation</refpurpose>
    </refnamediv>
    <refsynopsisdiv>
        <title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glBeginTransformFeedback</function></funcdef>
                <paramdef>GLenum <parameter>primitiveMode</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glEndTransformFeedback</function></funcdef>
                <paramdef><parameter>void</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 xml:id="parameters"><title>Parameters for <function>glBeginTransformFeedback</function></title>
        <variablelist>
        <varlistentry>
            <term><parameter>primitiveMode</parameter></term>
            <listitem>
                <para>
                    Specify the output type of the primitives that will be recorded into the
                    buffer objects that are bound for transform feedback.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 xml:id="description"><title>Description</title>
        <para>
            Transform feedback mode captures the values of varying variables written by the vertex shader.
            Transform feedback is said to be active after a call to <function>glBeginTransformFeedback</function>
            until a subsequent call to <function>glEndTransformFeedback</function>.
            Transform feedback commands must be paired. An implicit <citerefentry><refentrytitle>glResumeTransformFeedback</refentrytitle></citerefentry>
            is performed by <function>glEndTransformFeedback</function> if the transform feedback is paused.
            Transform feedback is restricted to non-indexed <constant>GL_POINTS</constant>, <constant>GL_LINES</constant>, and
            <constant>GL_TRIANGLES</constant>.
        </para>
        <para>
            While transform feedback is active the <parameter>mode</parameter> parameter to
            <citerefentry><refentrytitle>glDrawArrays</refentrytitle></citerefentry> must exactly match the
            <parameter>primitiveMode</parameter> specified by <function>glBeginTransformFeedback</function>.
        </para>
    </refsect1>
    <refsect1 xml:id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <function>glBeginTransformFeedback</function> is executed
            while transform feedback is active.
        </para>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated by <function>glBeginTransformFeedback</function> if <parameter>primitiveMode</parameter>
            is not one of  <constant>GL_POINTS</constant>, <constant>GL_LINES</constant>, or <constant>GL_TRIANGLES</constant>.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <function>glEndTransformFeedback</function> is executed
            while transform feedback is not active.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated by <citerefentry><refentrytitle>glDrawArrays</refentrytitle></citerefentry>
            and <citerefentry><refentrytitle>glDrawArraysInstanced</refentrytitle></citerefentry> if transform feedback is active
            and <parameter>mode</parameter> does not exactly match <parameter>primitiveMode</parameter>.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated by <citerefentry><refentrytitle>glDrawElements</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glDrawElementsInstanced</refentrytitle></citerefentry>, and
            <citerefentry><refentrytitle>glDrawRangeElements</refentrytitle></citerefentry> if transform feedback is active and not paused.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated by <function>glBeginTransformFeedback</function> if any binding
            point used in transform feedback mode does not have a buffer object bound. In interleaved mode, only the first buffer
            object binding point is ever written to.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated by <function>glBeginTransformFeedback</function> if no binding
            points would be used, either because no program object is active of because the active program object has specified
            no varying variables to record.
        </para>
    </refsect1>
    <refsect1 xml:id="versions">
        <title>API Version Support</title>
        <informaltable>
            <tgroup cols="4" align="left">
                <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
                <tbody>
                    <row>
                        <entry><function>glBeginTransformFeedback</function></entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es30']/*)"/>
                    </row>
                    <row>
                        <entry><function>glEndTransformFeedback</function></entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es30']/*)"/>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glPauseTransformFeedback</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glResumeTransformFeedback</refentrytitle></citerefentry>
        </para>
    </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>
