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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glGetActiveAttrib">
    <info>
        <copyright>
            <year>2003-2005</year>
            <holder>3Dlabs Inc. Ltd.</holder>
        </copyright>
        <copyright>
            <year>2010-2014</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>glGetActiveAttrib</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glGetActiveAttrib</refname>
        <refpurpose>Returns information about an active attribute variable for the specified program object</refpurpose>
    </refnamediv>
    <refsynopsisdiv>
        <title>C Specification</title>
    <funcsynopsis>
        <funcprototype>
        <funcdef>void <function>glGetActiveAttrib</function></funcdef>
        <paramdef>GLuint <parameter>program</parameter></paramdef>
        <paramdef>GLuint <parameter>index</parameter></paramdef>
        <paramdef>GLsizei <parameter>bufSize</parameter></paramdef>
        <paramdef>GLsizei *<parameter>length</parameter></paramdef>
        <paramdef>GLint *<parameter>size</parameter></paramdef>
        <paramdef>GLenum *<parameter>type</parameter></paramdef>
        <paramdef>GLchar *<parameter>name</parameter></paramdef>
        </funcprototype>
    </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 xml:id="parameters"><title>Parameters</title>
    <variablelist>
        <varlistentry>
        <term><parameter>program</parameter></term>
        <listitem>
            <para>Specifies the program object to be
            queried.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>index</parameter></term>
        <listitem>
            <para>Specifies the index of the attribute variable
            to be queried.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>bufSize</parameter></term>
        <listitem>
            <para>Specifies the maximum number of characters
            OpenGL is allowed to write in the character buffer
            indicated by <parameter>name</parameter>.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>length</parameter></term>
        <listitem>
            <para>Returns the number of characters actually
            written by OpenGL in the string indicated by
            <parameter>name</parameter> (excluding the null
            terminator) if a value other than
            <constant>NULL</constant> is passed.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>size</parameter></term>
        <listitem>
            <para>Returns the size of the attribute
            variable.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>type</parameter></term>
        <listitem>
            <para>Returns the data type of the attribute
            variable.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>name</parameter></term>
        <listitem>
            <para>Returns a null terminated string containing
            the name of the attribute variable.</para>
        </listitem>
        </varlistentry>
    </variablelist>
    </refsect1>
    <refsect1 xml:id="description"><title>Description</title>
    <para><function>glGetActiveAttrib</function> returns information
    about an active attribute variable in the program object
    specified by <parameter>program</parameter>. The number of
    active attributes can be obtained by calling
    <citerefentry><refentrytitle>glGetProgramiv</refentrytitle></citerefentry>
    with the value <constant>GL_ACTIVE_ATTRIBUTES</constant>. A
    value of zero for <parameter>index</parameter> selects the first
    active attribute variable. Permissible values for
    <parameter>index</parameter> range from zero to the number of
    active attribute variables minus one.</para>

    <para>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,
    <parameter>program</parameter> should have previously been the
    target of a call to
    <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
    but it is not necessary for it to have been linked
    successfully.</para>

    <para>The size of the character buffer required to store the
    longest attribute variable name in
    <parameter>program</parameter> can be obtained by calling
    <citerefentry><refentrytitle>glGetProgramiv</refentrytitle></citerefentry>
    with the value
    <constant>GL_ACTIVE_ATTRIBUTE_MAX_LENGTH</constant>. 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 <parameter>bufSize</parameter>, and a pointer to
    this character buffer is passed in
    <parameter>name</parameter>.</para>

    <para><function>glGetActiveAttrib</function> returns the name of
    the attribute variable indicated by
    <parameter>index</parameter>, storing it in the character buffer
    specified by <parameter>name</parameter>. The string returned
    will be null terminated. The actual number of characters written
    into this buffer is returned in <parameter>length</parameter>,
    and this count does not include the null termination character.
    If the length of the returned string is not required, a value of
    <constant>NULL</constant> can be passed in the
    <parameter>length</parameter> argument.</para>

    <para>The <parameter>type</parameter> argument will return a
    pointer to the attribute variable's data type. The symbolic
    constants <constant>GL_FLOAT</constant>,
    <constant>GL_FLOAT_VEC2</constant>,
    <constant>GL_FLOAT_VEC3</constant>,
    <constant>GL_FLOAT_VEC4</constant>,
    <constant>GL_FLOAT_MAT2</constant>,
    <constant>GL_FLOAT_MAT3</constant>,
    <constant>GL_FLOAT_MAT4</constant>,
    <constant>GL_FLOAT_MAT2x3</constant>,
    <constant>GL_FLOAT_MAT2x4</constant>,
    <constant>GL_FLOAT_MAT3x2</constant>,
    <constant>GL_FLOAT_MAT3x4</constant>,
    <constant>GL_FLOAT_MAT4x2</constant>,
    <constant>GL_FLOAT_MAT4x3</constant>,
    <constant>GL_INT</constant>,
    <constant>GL_INT_VEC2</constant>,
    <constant>GL_INT_VEC3</constant>,
    <constant>GL_INT_VEC4</constant>,
    <constant>GL_UNSIGNED_INT</constant>,
    <constant>GL_UNSIGNED_INT_VEC2</constant>,
    <constant>GL_UNSIGNED_INT_VEC3</constant>, or
    <constant>GL_UNSIGNED_INT_VEC4</constant> may be returned. The
    <parameter>size</parameter> argument will return the size of the
    attribute, in units of the type returned in
    <parameter>type</parameter>.</para>

    <para>This function will return as much information as it can
    about the specified active attribute variable. If no information
    is available, <parameter>length</parameter> will be 0, and
    <parameter>name</parameter> 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
    <parameter>length</parameter>, <parameter>size</parameter>,
    <parameter>type</parameter>, and <parameter>name</parameter>
    will be unmodified.</para>
    </refsect1>
    <refsect1 xml:id="errors"><title>Errors</title>
    <para><constant>GL_INVALID_VALUE</constant> is generated if
    <parameter>program</parameter> is not a value generated by
    OpenGL.</para>

    <para><constant>GL_INVALID_OPERATION</constant> is generated if
    <parameter>program</parameter> is not a program object.</para>

    <para><constant>GL_INVALID_VALUE</constant> is generated if
    <parameter>index</parameter> is greater than or equal to the
    number of active attribute variables in
    <parameter>program</parameter>.</para>

    <para><constant>GL_INVALID_VALUE</constant> is generated if
    <parameter>bufSize</parameter> is less than 0.</para>
    </refsect1>
    <refsect1 xml:id="associatedgets"><title>Associated Gets</title>
    <para><citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
    with argument <constant>GL_MAX_VERTEX_ATTRIBS</constant>.</para>

    <para><citerefentry><refentrytitle>glGetProgramiv</refentrytitle></citerefentry>
    with argument <constant>GL_ACTIVE_ATTRIBUTES</constant> or
    <constant>GL_ACTIVE_ATTRIBUTE_MAX_LENGTH</constant>.</para>

    <para><citerefentry><refentrytitle>glIsProgram</refentrytitle></citerefentry></para>
    </refsect1>
    <refsect1 xml:id="versions">
        <title>API Version Support</title>
        <informaltable>
            <tgroup cols="4" align="left">
                <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
                <tbody>
                    <row>
                        <entry>glGetActiveAttrib</entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es20']/*)"/>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
    <para><citerefentry><refentrytitle>glBindAttribLocation</refentrytitle></citerefentry>,
    <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
    <citerefentry><refentrytitle>glVertexAttrib</refentrytitle></citerefentry>,
    <citerefentry><refentrytitle>glVertexAttribPointer</refentrytitle></citerefentry></para>
    </refsect1>
    <refsect1 xml:id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"/> 2003-2005 3Dlabs Inc. Ltd.
            Copyright <trademark class="copyright"/> 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.
            <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://opencontent.org/openpub/">http://opencontent.org/openpub/</link>.
        </para>
    </refsect1>
</refentry>
