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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glTransformFeedbackVaryings">
    <info>
        <copyright>
            <year>2010-2013</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>glTransformFeedbackVaryings</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glTransformFeedbackVaryings</refname>
        <refpurpose>specify values to record in transform feedback buffers</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glTransformFeedbackVaryings</function></funcdef>
                <paramdef>GLuint<parameter>program</parameter></paramdef>
                <paramdef>GLsizei<parameter>count</parameter></paramdef>
                <paramdef>const char **<parameter>varyings</parameter></paramdef>
                <paramdef>GLenum<parameter>bufferMode</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 xml:id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>program</parameter></term>
            <listitem>
                <para>
                    The name of the target program object.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>count</parameter></term>
            <listitem>
                <para>
                    The number of varying variables used for transform feedback.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>varyings</parameter></term>
            <listitem>
                <para>
                    An array of <parameter>count</parameter> zero-terminated strings specifying the
                    names of the varying variables to use for transform feedback.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>bufferMode</parameter></term>
            <listitem>
                <para>
                    Identifies the mode used to capture the varying variables when transform feedback is active.
                    <parameter>bufferMode</parameter> must be <constant>GL_INTERLEAVED_ATTRIBS</constant> or <constant>GL_SEPARATE_ATTRIBS</constant>.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 xml:id="description"><title>Description</title>
        <para>
            The names of the vertex or geometry shader outputs to be recorded in transform feedback mode
            are specified using <function>glTransformFeedbackVaryings</function>. When a geometry shader
            is active, transform feedback records the values of selected geometry shader output variables
            from the emitted vertices. Otherwise, the values of the selected vertex shader outputs are
            recorded.
        </para>
        <para>
            The state set by <function>glTranformFeedbackVaryings</function> is stored and takes effect
            next time <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry> is called
            on <parameter>program</parameter>. When <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>
            is called, <parameter>program</parameter> is linked so that the values of the specified varying variables
            for the vertices of each primitive generated by the GL are written to a single buffer
            object if <parameter>bufferMode</parameter> is <constant>GL_INTERLEAVED_ATTRIBS</constant> or multiple
            buffer objects if <parameter>bufferMode</parameter> is <constant>GL_SEPARATE_ATTRIBS</constant>.
        </para>
        <para>
            In addition to the errors generated by <function>glTransformFeedbackVaryings</function>, the
            program <parameter>program</parameter> will fail to link if:
            <itemizedlist>
                <listitem>
                    <para>
                        The count specified by <function>glTransformFeedbackVaryings</function> is non-zero, but the
                        program object has no vertex or geometry shader.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        Any variable name specified in the <parameter>varyings</parameter> array is not declared as an output
                        in the vertex shader (or the geometry shader, if active).
                    </para>
                </listitem>
                <listitem>
                    <para>
                        Any two entries in the <parameter>varyings</parameter> array specify the same varying variable.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        The total number of components to capture in any varying variable in <parameter>varyings</parameter>
                        is greater than the constant <constant>GL_MAX_TRANSFORM_FEEDBACK_SEPARATE_COMPONENTS</constant>
                        and the buffer mode is <constant>GL_SEPARATE_ATTRIBS</constant>.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        The total number of components to capture is greater than the constant
                        <constant>GL_MAX_TRANSFORM_FEEDBACK_INTERLEAVED_COMPONENTS</constant> and the buffer
                        mode is <constant>GL_INTERLEAVED_ATTRIBS</constant>.
                    </para>
                </listitem>
            </itemizedlist>
        </para>
    </refsect1>
    <refsect1 xml:id="notes"><title>Notes</title>
        <para>
            <function>glGetTransformFeedbackVarying</function> is available only if the GL version is 3.0 or greater.
        </para>
    </refsect1>
    <refsect1 xml:id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_VALUE</constant> is generated if <parameter>program</parameter> is not
            the name of a program object.
        </para>
        <para>
            <constant>GL_INVALID_VALUE</constant> is generated if <parameter>bufferMode</parameter> is <constant>GL_SEPARATE_ATTRIBS</constant>
            and <parameter>count</parameter> is greater than the implementation-dependent limit <constant>GL_MAX_TRANSFORM_FEEDBACK_SEPARATE_ATTRIBS</constant>.
        </para>
    </refsect1>
        <refsect1 xml:id="associatedgets"><title>Associated Gets</title>
        <para>
            <citerefentry><refentrytitle>glGetTransformFeedbackVarying</refentrytitle></citerefentry>
        </para>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glBeginTransformFeedback</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glEndTransformFeedback</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glGetTransformFeedbackVarying</refentrytitle></citerefentry>
        </para>
    </refsect1>    <refsect1 xml:id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"/> 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.
            <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://opencontent.org/openpub/">http://opencontent.org/openpub/</link>.
        </para>
    </refsect1>
</refentry>
