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+<?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" pref:renderer="mathplayer-dl"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><link rel="stylesheet" type="text/css" href="opengl-man.css" /><title>glGetTransformFeedbackVarying</title><meta name="generator" content="DocBook XSL Stylesheets V1.69.1" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="glGetTransformFeedbackVarying"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glGetTransformFeedbackVarying — retrieve information about varying variables selected for transform feedback</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr><td><code class="funcdef">void <b class="fsfunc">glGetTransformFeedbackVarying</b>(</code></td><td>GLuint </td><td><var class="pdparam">program</var>, </td></tr><tr><td> </td><td>GLuint </td><td><var class="pdparam">index</var>, </td></tr><tr><td> </td><td>GLsizei </td><td><var class="pdparam">bufSize</var>, </td></tr><tr><td> </td><td>GLsizei * </td><td><var class="pdparam">length</var>, </td></tr><tr><td> </td><td>GLsizei </td><td><var class="pdparam">size</var>, </td></tr><tr><td> </td><td>GLenum * </td><td><var class="pdparam">type</var>, </td></tr><tr><td> </td><td>char * </td><td><var class="pdparam">name</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>program</code></em></span></dt><dd><p>
+ The name of the target program object.
+ </p></dd><dt><span class="term"><em class="parameter"><code>index</code></em></span></dt><dd><p>
+ The index of the varying variable whose information to retrieve.
+ </p></dd><dt><span class="term"><em class="parameter"><code>bufSize</code></em></span></dt><dd><p>
+ The maximum number of characters, including the null terminator, that may be written into <em class="parameter"><code>name</code></em>.
+ </p></dd><dt><span class="term"><em class="parameter"><code>length</code></em></span></dt><dd><p>
+ The address of a variable which will receive the number of characters written into <em class="parameter"><code>name</code></em>,
+ excluding the null-terminator. If <em class="parameter"><code>length</code></em> is <code class="constant">NULL</code> no length is returned.
+ </p></dd><dt><span class="term"><em class="parameter"><code>size</code></em></span></dt><dd><p>
+ The address of a variable that will receive the size of the varying.
+ </p></dd><dt><span class="term"><em class="parameter"><code>type</code></em></span></dt><dd><p>
+ The address of a variable that will recieve the type of the varying.
+ </p></dd><dt><span class="term"><em class="parameter"><code>name</code></em></span></dt><dd><p>
+ The address of a buffer into which will be written the name of the varying.
+ </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
+ Information about the set of varying variables in a linked program that will be captured
+ during transform feedback may be retrieved by calling <code class="function">glGetTransformFeedbackVarying</code>.
+ <code class="function">glGetTransformFeedbackVarying</code> provides information about the varying
+ variable selected by <em class="parameter"><code>index</code></em>. An <em class="parameter"><code>index</code></em> of 0 selects
+ the first varying variable specified in the <em class="parameter"><code>varyings</code></em> array passed
+ to <a href="glTransformFeedbackVaryings.xml"><span class="citerefentry"><span class="refentrytitle">glTransformFeedbackVaryings</span></span></a>, and
+ an <em class="parameter"><code>index</code></em> of <code class="constant">GL_TRANSFORM_FEEDBACK_VARYINGS-1</code> selects
+ the last such variable.
+ </p><p>
+ The name of the selected varying is returned as a null-terminated string in
+ <em class="parameter"><code>name</code></em>. The actual number of characters written into <em class="parameter"><code>name</code></em>,
+ excluding the null terminator, is returned in <em class="parameter"><code>length</code></em>. If <em class="parameter"><code>length</code></em>
+ is NULL, no length is returned. The maximum number of characters that may be written into <em class="parameter"><code>name</code></em>,
+ including the null terminator, is specified by <em class="parameter"><code>bufSize</code></em>.
+ </p><p>
+ The length of the longest varying name in program is given by <code class="constant">GL_TRANSFORM_FEEDBACK_VARYING_MAX_LENGTH</code>,
+ which can be queried with <a href="glGetProgram.xml"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a>.
+ </p><p>
+ For the selected varying variable, its type is returned into <em class="parameter"><code>type</code></em>. The size of
+ the varying is returned into <em class="parameter"><code>size</code></em>. The value in <em class="parameter"><code>size</code></em> is
+ in units of the type returned in <em class="parameter"><code>type</code></em>. The type returned can be any of the
+ scalar, vector, or matrix attribute types returned by <a href="glGetActiveAttrib.xml"><span class="citerefentry"><span class="refentrytitle">glGetActiveAttrib</span></span></a>.
+ If an error occurred, the return parameters <em class="parameter"><code>length</code></em>, <em class="parameter"><code>size</code></em>,
+ <em class="parameter"><code>type</code></em> and <em class="parameter"><code>name</code></em> will be unmodified. This command will return as much
+ information about the varying variables as possible. If no information is available, <em class="parameter"><code>length</code></em>
+ will be set to zero and <em class="parameter"><code>name</code></em> will be an empty string. This situation could
+ arise if <code class="function">glGetTransformFeedbackVarying</code> is called after a failed link.
+ </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p>
+ <code class="constant">GL_INVALID_VALUE</code> is generated if <em class="parameter"><code>program</code></em> is not
+ the name of a program object.
+ </p><p>
+ <code class="constant">GL_INVALID_VALUE</code> is generated if <em class="parameter"><code>index</code></em> is greater or equal to
+ the value of <code class="constant">GL_TRANSFORM_FEEDBACK_VARYINGS</code>.
+ </p><p>
+ <code class="constant">GL_INVALID_OPERATION</code> is generated <em class="parameter"><code>program</code></em> has not been linked.
+ </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p>
+ <a href="glGetProgram.xml"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a> with argument <code class="constant">GL_TRANSFORM_FEEDBACK_VARYING_MAX_LENGTH</code>.
+ </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
+ <a href="glBeginTransformFeedback.xml"><span class="citerefentry"><span class="refentrytitle">glBeginTransformFeedback</span></span></a>,
+ <a href="glEndTransformFeedback.xml"><span class="citerefentry"><span class="refentrytitle">glEndTransformFeedback</span></span></a>,
+ <a href="glTransformFeedbackVaryings.xml"><span class="citerefentry"><span class="refentrytitle">glTransformFeedbackVaryings</span></span></a>,
+ <a href="glGetProgram.xml"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a>
+ </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
+ Copyright <span class="trademark"></span>© 2010 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.
+ <a href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
+ </p></div></div></body></html>
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