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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html><html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>glGetActiveAttrib - OpenGL 4 Reference Pages</title>
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<div class="refentry" id="glGetActiveAttrib">
<div class="titlepage"/>
<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 style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">
<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" id="parameters">
<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" id="description">
<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.xhtml"><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.xhtml"><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.xhtml"><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" id="errors">
<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" id="associatedgets">
<h2>Associated Gets</h2>
<p><a class="citerefentry" href="glGet.xhtml"><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.xhtml"><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.xhtml">
<span class="citerefentry">
<span class="refentrytitle">glIsProgram</span>
</span>
</a>
</p>
</div>
<div class="refsect1" id="versions">
<h2>Version Support</h2>
<div class="informaltable">
<table style="border-collapse: collapse; border-top: 2px solid ; border-bottom: 2px solid ; border-left: 2px solid ; border-right: 2px solid ; ">
<colgroup>
<col style="text-align: left; "/>
<col style="text-align: center; " class="firstvers"/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; "/>
<col style="text-align: center; " class="lastvers"/>
</colgroup>
<thead>
<tr>
<th style="text-align: left; border-right: 2px solid ; ">
</th>
<th style="text-align: center; border-bottom: 2px solid ; " colspan="12">
<span class="bold"><strong>OpenGL Version</strong></span>
</th>
</tr>
<tr>
<th style="text-align: left; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>Function / Feature Name</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>2.0</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>2.1</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>3.0</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>3.1</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>3.2</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>3.3</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.0</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.1</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.2</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.3</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.4</strong></span>
</th>
<th style="text-align: center; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.5</strong></span>
</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align: left; border-right: 2px solid ; ">
<code class="function">glGetActiveAttrib</code>
</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; ">✔</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="refsect1" id="seealso">
<h2>See Also</h2>
<p><a class="citerefentry" href="glBindAttribLocation.xhtml"><span class="citerefentry"><span class="refentrytitle">glBindAttribLocation</span></span></a>,
<a class="citerefentry" href="glLinkProgram.xhtml"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a>,
<a class="citerefentry" href="glVertexAttrib.xhtml"><span class="citerefentry"><span class="refentrytitle">glVertexAttrib</span></span></a>,
<a class="citerefentry" href="glVertexAttribPointer.xhtml"><span class="citerefentry"><span class="refentrytitle">glVertexAttribPointer</span></span></a></p>
</div>
<div class="refsect1" id="Copyright">
<h2>Copyright</h2>
<p>
Copyright <span class="trademark"/>© 2003-2005 3Dlabs Inc. Ltd.
Copyright <span class="trademark"/>© 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.
<a class="link" href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
</p>
</div>
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