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<!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="glGetTransformFeedbackVarying">
<info>
<copyright>
<year>2010-2014</year>
<holder>Khronos Group</holder>
</copyright>
</info>
<refmeta>
<refentrytitle>glGetTransformFeedbackVarying</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>glGetTransformFeedbackVarying</refname>
<refpurpose>retrieve information about varying variables selected for transform feedback</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glGetTransformFeedbackVarying</function></funcdef>
<paramdef>GLuint<parameter>program</parameter></paramdef>
<paramdef>GLuint<parameter>index</parameter></paramdef>
<paramdef>GLsizei<parameter>bufSize</parameter></paramdef>
<paramdef>GLsizei *<parameter>length</parameter></paramdef>
<paramdef>GLsizei *<parameter>size</parameter></paramdef>
<paramdef>GLenum *<parameter>type</parameter></paramdef>
<paramdef>char *<parameter>name</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>index</parameter></term>
<listitem>
<para>
The index of the varying variable whose information to retrieve.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>bufSize</parameter></term>
<listitem>
<para>
The maximum number of characters, including the null terminator, that may be written into <parameter>name</parameter>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>length</parameter></term>
<listitem>
<para>
The address of a variable which will receive the number of characters written into <parameter>name</parameter>,
excluding the null-terminator. If <parameter>length</parameter> is <constant>NULL</constant> no length is returned.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>size</parameter></term>
<listitem>
<para>
The address of a variable that will receive the size of the varying.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>type</parameter></term>
<listitem>
<para>
The address of a variable that will recieve the type of the varying.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>name</parameter></term>
<listitem>
<para>
The address of a buffer into which will be written the name of the varying.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 xml:id="description"><title>Description</title>
<para>
Information about the set of varying variables in a linked program that will be captured
during transform feedback may be retrieved by calling <function>glGetTransformFeedbackVarying</function>.
<function>glGetTransformFeedbackVarying</function> provides information about the varying
variable selected by <parameter>index</parameter>. An <parameter>index</parameter> of 0 selects
the first varying variable specified in the <parameter>varyings</parameter> array passed
to <citerefentry><refentrytitle>glTransformFeedbackVaryings</refentrytitle></citerefentry>, and
an <parameter>index</parameter> of the value of
<constant>GL_TRANSFORM_FEEDBACK_VARYINGS</constant> minus one selects
the last such variable.
</para>
<para>
The name of the selected varying is returned as a null-terminated string in
<parameter>name</parameter>. The actual number of characters written into <parameter>name</parameter>,
excluding the null terminator, is returned in <parameter>length</parameter>. If <parameter>length</parameter>
is NULL, no length is returned. The maximum number of characters that may be written into <parameter>name</parameter>,
including the null terminator, is specified by <parameter>bufSize</parameter>.
</para>
<para>
The length of the longest varying name in program is given by <constant>GL_TRANSFORM_FEEDBACK_VARYING_MAX_LENGTH</constant>,
which can be queried with <citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>.
</para>
<para>
For the selected varying variable, its type is returned into <parameter>type</parameter>. The size of
the varying is returned into <parameter>size</parameter>. The value in <parameter>size</parameter> is
in units of the type returned in <parameter>type</parameter>. The type returned can be any of the
scalar, vector, or matrix attribute types returned by <citerefentry><refentrytitle>glGetActiveAttrib</refentrytitle></citerefentry>.
If an error occurred, the return parameters <parameter>length</parameter>, <parameter>size</parameter>,
<parameter>type</parameter> and <parameter>name</parameter> will be unmodified. This command will return as much
information about the varying variables as possible. If no information is available, <parameter>length</parameter>
will be set to zero and <parameter>name</parameter> will be an empty string. This situation could
arise if <function>glGetTransformFeedbackVarying</function> is called after a failed link.
</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>index</parameter> is greater or equal to
the value of <constant>GL_TRANSFORM_FEEDBACK_VARYINGS</constant>.
</para>
<para>
<constant>GL_INVALID_OPERATION</constant> is generated <parameter>program</parameter> has not been linked.
</para>
</refsect1>
<refsect1 xml:id="associatedgets"><title>Associated Gets</title>
<para>
<citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry> with argument <constant>GL_TRANSFORM_FEEDBACK_VARYING_MAX_LENGTH</constant>.
</para>
</refsect1>
<refsect1 xml:id="versions"><title>Version Support</title>
<informaltable>
<tgroup cols="13" align="left">
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
<tbody>
<row>
<entry><function>glGetTransformFeedbackVarying</function></entry>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='30']/*)"/>
</row>
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 xml:id="seealso"><title>See Also</title>
<para>
<citerefentry><refentrytitle>glBeginTransformFeedback</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glEndTransformFeedback</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glTransformFeedbackVaryings</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glGetProgram</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>
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