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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd">
<?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>glGetActiveAttrib - OpenGL 4 Reference Pages</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1" /></head><body><div class="refentry"><a id="glGetActiveAttrib"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glGetActiveAttrib — Returns information about an active attribute variable for the specified program object</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void <strong class="fsfunc">glGetActiveAttrib</strong>(</code></td><td>GLuint <var class="pdparam">program</var>, </td></tr><tr><td> </td><td>GLuint <var class="pdparam">index</var>, </td></tr><tr><td> </td><td>GLsizei <var class="pdparam">bufSize</var>, </td></tr><tr><td> </td><td>GLsizei *<var class="pdparam">length</var>, </td></tr><tr><td> </td><td>GLint *<var class="pdparam">size</var>, </td></tr><tr><td> </td><td>GLenum *<var class="pdparam">type</var>, </td></tr><tr><td> </td><td>GLchar *<var class="pdparam">name</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>program</code></em></span></dt><dd><p>Specifies the program object to be
queried.</p></dd><dt><span class="term"><em class="parameter"><code>index</code></em></span></dt><dd><p>Specifies the index of the attribute variable
to be queried.</p></dd><dt><span class="term"><em class="parameter"><code>bufSize</code></em></span></dt><dd><p>Specifies the maximum number of characters
OpenGL is allowed to write in the character buffer
indicated by <em class="parameter"><code>name</code></em>.</p></dd><dt><span class="term"><em class="parameter"><code>length</code></em></span></dt><dd><p>Returns the number of characters actually
written by OpenGL in the string indicated by
<em class="parameter"><code>name</code></em> (excluding the null
terminator) if a value other than
<code class="constant">NULL</code> is passed.</p></dd><dt><span class="term"><em class="parameter"><code>size</code></em></span></dt><dd><p>Returns the size of the attribute
variable.</p></dd><dt><span class="term"><em class="parameter"><code>type</code></em></span></dt><dd><p>Returns the data type of the attribute
variable.</p></dd><dt><span class="term"><em class="parameter"><code>name</code></em></span></dt><dd><p>Returns a null terminated string containing
the name of the attribute variable.</p></dd></dl></div></div><div class="refsect1"><a id="description"></a><h2>Description</h2><p><code class="function">glGetActiveAttrib</code> returns information
about an active attribute variable in the program object
specified by <em class="parameter"><code>program</code></em>. The number of
active attributes can be obtained by calling
<a class="citerefentry" href="glGetProgram.xml"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a>
with the value <code class="constant">GL_ACTIVE_ATTRIBUTES</code>. A
value of 0 for <em class="parameter"><code>index</code></em> selects the first
active attribute variable. Permissible values for
<em class="parameter"><code>index</code></em> range from zero to the number of
active attribute variables minus one.</p><p>A vertex shader may use either built-in attribute
variables, user-defined attribute variables, or both. Built-in
attribute variables have a prefix of "gl_" and
reference conventional OpenGL vertex attribtes (e.g.,
<em class="parameter"><code>gl_Vertex</code></em>,
<em class="parameter"><code>gl_Normal</code></em>, etc., see the OpenGL Shading
Language specification for a complete list.) User-defined
attribute variables have arbitrary names and obtain their values
through numbered generic vertex attributes. An attribute
variable (either built-in or user-defined) is considered active
if it is determined during the link operation that it may be
accessed during program execution. Therefore,
<em class="parameter"><code>program</code></em> should have previously been the
target of a call to
<a class="citerefentry" href="glLinkProgram.xml"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a>,
but it is not necessary for it to have been linked
successfully.</p><p>The size of the character buffer required to store the
longest attribute variable name in
<em class="parameter"><code>program</code></em> can be obtained by calling
<a class="citerefentry" href="glGetProgram.xml"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a>
with the value
<code class="constant">GL_ACTIVE_ATTRIBUTE_MAX_LENGTH</code>. This value
should be used to allocate a buffer of sufficient size to store
the returned attribute name. The size of this character buffer
is passed in <em class="parameter"><code>bufSize</code></em>, and a pointer to
this character buffer is passed in
<em class="parameter"><code>name</code></em>.</p><p><code class="function">glGetActiveAttrib</code> returns the name of
the attribute variable indicated by
<em class="parameter"><code>index</code></em>, storing it in the character buffer
specified by <em class="parameter"><code>name</code></em>. The string returned
will be null terminated. The actual number of characters written
into this buffer is returned in <em class="parameter"><code>length</code></em>,
and this count does not include the null termination character.
If the length of the returned string is not required, a value of
<code class="constant">NULL</code> can be passed in the
<em class="parameter"><code>length</code></em> argument.</p><p>The <em class="parameter"><code>type</code></em> argument specifies a
pointer to a variable into which the attribute variable's data type
will be written. The symbolic
constants <code class="constant">GL_FLOAT</code>,
<code class="constant">GL_FLOAT_VEC2</code>,
<code class="constant">GL_FLOAT_VEC3</code>,
<code class="constant">GL_FLOAT_VEC4</code>,
<code class="constant">GL_FLOAT_MAT2</code>,
<code class="constant">GL_FLOAT_MAT3</code>,
<code class="constant">GL_FLOAT_MAT4</code>,
<code class="constant">GL_FLOAT_MAT2x3</code>,
<code class="constant">GL_FLOAT_MAT2x4</code>,
<code class="constant">GL_FLOAT_MAT3x2</code>,
<code class="constant">GL_FLOAT_MAT3x4</code>,
<code class="constant">GL_FLOAT_MAT4x2</code>,
<code class="constant">GL_FLOAT_MAT4x3</code>,
<code class="constant">GL_INT</code>,
<code class="constant">GL_INT_VEC2</code>,
<code class="constant">GL_INT_VEC3</code>,
<code class="constant">GL_INT_VEC4</code>,
<code class="constant">GL_UNSIGNED_INT</code>,
<code class="constant">GL_UNSIGNED_INT_VEC2</code>,
<code class="constant">GL_UNSIGNED_INT_VEC3</code>,
<code class="constant">GL_UNSIGNED_INT_VEC4</code>,
<code class="constant">GL_DOUBLE</code>,
<code class="constant">GL_DOUBLE_VEC2</code>,
<code class="constant">GL_DOUBLE_VEC3</code>,
<code class="constant">GL_DOUBLE_VEC4</code>,
<code class="constant">GL_DOUBLE_MAT2</code>,
<code class="constant">GL_DOUBLE_MAT3</code>,
<code class="constant">GL_DOUBLE_MAT4</code>,
<code class="constant">GL_DOUBLE_MAT2x3</code>,
<code class="constant">GL_DOUBLE_MAT2x4</code>,
<code class="constant">GL_DOUBLE_MAT3x2</code>,
<code class="constant">GL_DOUBLE_MAT3x4</code>,
<code class="constant">GL_DOUBLE_MAT4x2</code>, or
<code class="constant">GL_DOUBLE_MAT4x3</code>
may be returned. The
<em class="parameter"><code>size</code></em> argument will return the size of the
attribute, in units of the type returned in
<em class="parameter"><code>type</code></em>.</p><p>The list of active attribute variables may include both
built-in attribute variables (which begin with the prefix
"gl_") as well as user-defined attribute variable
names.</p><p>This function will return as much information as it can
about the specified active attribute variable. If no information
is available, <em class="parameter"><code>length</code></em> will be 0, and
<em class="parameter"><code>name</code></em> will be an empty string. This
situation could occur if this function is called after a link
operation that failed. If an error occurs, the return values
<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.</p></div><div class="refsect1"><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 a value generated by
OpenGL.</p><p><code class="constant">GL_INVALID_OPERATION</code> is generated if
<em class="parameter"><code>program</code></em> is not a program object.</p><p><code class="constant">GL_INVALID_VALUE</code> is generated if
<em class="parameter"><code>index</code></em> is greater than or equal to the
number of active attribute variables in
<em class="parameter"><code>program</code></em>.</p><p><code class="constant">GL_INVALID_VALUE</code> is generated if
<em class="parameter"><code>bufSize</code></em> is less than 0.</p></div><div class="refsect1"><a id="associatedgets"></a><h2>Associated Gets</h2><p><a class="citerefentry" href="glGet.xml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a>
with argument <code class="constant">GL_MAX_VERTEX_ATTRIBS</code>.</p><p><a class="citerefentry" href="glGetProgram.xml"><span class="citerefentry"><span class="refentrytitle">glGetProgram</span></span></a>
with argument <code class="constant">GL_ACTIVE_ATTRIBUTES</code> or
<code class="constant">GL_ACTIVE_ATTRIBUTE_MAX_LENGTH</code>.</p><p><a class="citerefentry" href="glIsProgram.xml"><span class="citerefentry"><span class="refentrytitle">glIsProgram</span></span></a></p></div><div class="refsect1"><a id="seealso"></a><h2>See Also</h2><p><a class="citerefentry" href="glBindAttribLocation.xml"><span class="citerefentry"><span class="refentrytitle">glBindAttribLocation</span></span></a>,
<a class="citerefentry" href="glLinkProgram.xml"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a>,
<a class="citerefentry" href="glVertexAttrib.xml"><span class="citerefentry"><span class="refentrytitle">glVertexAttrib</span></span></a>,
<a class="citerefentry" href="glVertexAttribPointer.xml"><span class="citerefentry"><span class="refentrytitle">glVertexAttribPointer</span></span></a></p></div><div class="refsect1"><a id="Copyright"></a><h2>Copyright</h2><p>
Copyright <span class="trademark"></span>© 2003-2005 3Dlabs Inc. Ltd.
Copyright <span class="trademark"></span>© 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.
<a class="ulink" href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
</p></div></div></body></html>
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