<div class="refentry" lang="en" xml:lang="en"><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><tr><td><code class="funcdef">void <b class="fsfunc">glGetActiveAttrib</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>GLint * </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>GLchar * </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>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" lang="en" xml:lang="en"><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 href="glGetProgram"><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 0 to the number of

active attribute variables minus 1.</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 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 href="glGetProgram"><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 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>,

<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>, or

<code class="constant">GL_UNSIGNED_INT_VEC4</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" 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 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" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p><a 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 href="glGetProgram"><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 href="glIsProgram"><span class="citerefentry"><span class="refentrytitle">glIsProgram</span></span></a></p></div>

{$pipelinestall}{$examples}

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

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

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

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

Copyright © 2003-2005 3Dlabs Inc. Ltd.

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

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