<div class="refentry"><a id="glGetActiveAttrib"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glGetActiveAttrib — return information about an active attribute variable</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table class="funcprototype-table" 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="glGetProgramiv"><span class="citerefentry"><span class="refentrytitle">glGetProgramiv</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 0 to the number of

active attribute variables minus 1.</p><p>Attribute variables have arbitrary names and obtain their values

through numbered generic vertex attributes. An attribute

variable 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"><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="glGetProgramiv"><span class="citerefentry"><span class="refentrytitle">glGetProgramiv</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 will return a

pointer to the attribute variable's data type. 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>, or

<code class="constant">GL_FLOAT_MAT4</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>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"><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="glGetProgramiv"><span class="citerefentry"><span class="refentrytitle">glGetProgramiv</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"><span class="citerefentry"><span class="refentrytitle">glIsProgram</span></span></a></p></div>

{$pipelinestall}{$examples}

<div class="refsect1"><a id="seealso"></a><h2>See Also</h2><p><a class="citerefentry" href="glBindAttribLocation"><span class="citerefentry"><span class="refentrytitle">glBindAttribLocation</span></span></a>,

<a class="citerefentry" href="glGetActiveUniform"><span class="citerefentry"><span class="refentrytitle">glGetActiveUniform</span></span></a>,

<a class="citerefentry" href="glLinkProgram"><span class="citerefentry"><span class="refentrytitle">glLinkProgram</span></span></a>,

<a class="citerefentry" href="glVertexAttrib"><span class="citerefentry"><span class="refentrytitle">glVertexAttrib</span></span></a>,

<a class="citerefentry" href="glVertexAttribPointer"><span class="citerefentry"><span class="refentrytitle">glVertexAttribPointer</span></span></a></p></div><div class="refsect1"><div id="Copyright"><h2>Copyright</h2><p>

Copyright © 2003-2005 3Dlabs Inc. Ltd.

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="https://opencontent.org/openpub/" target="_top">https://opencontent.org/openpub/</a>.

</p></div></div></div>