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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" /><title>glGetActiveAttrib</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 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 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 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>, or
	<code class="constant">GL_FLOAT_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="notes"></a><h2>Notes</h2><p><code class="function">glGetActiveAttrib</code>
	is available only if the GL version is 2.0 or greater.</p><p><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>, and
	<code class="constant">GL_FLOAT_MAT4x3</code>
	will only be returned as a <em class="parameter"><code>type</code></em>
        if the GL version is 2.1 or greater.</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_OPERATION</code> is generated if
	<code class="function">glGetActiveAttrib</code> is executed between the
	execution of
	<a class="citerefentry" href="glBegin.xml"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a>
	and the corresponding execution of
	<a class="citerefentry" href="glEnd.xml"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.</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. 
            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>