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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glGetUniformBlockIndex">
    <info>
        <copyright>
            <year>2010-2013</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>glGetUniformBlockIndex</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glGetUniformBlockIndex</refname>
        <refpurpose>retrieve the index of a named uniform block</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>GLuint <function>glGetUniformBlockIndex</function></funcdef>
                <paramdef>GLuint <parameter>program</parameter></paramdef>
                <paramdef>const GLchar *<parameter>uniformBlockName</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 xml:id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>program</parameter></term>
            <listitem>
                <para>
                    Specifies the name of a program containing the uniform block.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>uniformBlockName</parameter></term>
            <listitem>
                <para>
                    Specifies the address an array of characters to containing the name of the uniform block whose index to retrieve.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 xml:id="description"><title>Description</title>
        <para>
            <function>glGetUniformBlockIndex</function> retrieves the index of a uniform block within <parameter>program</parameter>.
        </para>
        <para>
            <parameter>program</parameter> must be the name of a program object for which the command
            <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry> must have been called in the past, although it is not required that
            <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry> must have succeeded. The link could have failed because the number
            of active uniforms exceeded the limit.
        </para>
        <para>
            <parameter>uniformBlockName</parameter> must contain a nul-terminated string specifying the name of the uniform block.
        </para>
        <para>
            <function>glGetUniformBlockIndex</function> returns the uniform block index for the uniform block named <parameter>uniformBlockName</parameter>
            of <parameter>program</parameter>. If <parameter>uniformBlockName</parameter> does not identify an active uniform block of <parameter>program</parameter>,
            <function>glGetUniformBlockIndex</function> returns the special identifier, <constant>GL_INVALID_INDEX</constant>. Indices of the active uniform
            blocks of a program are assigned in consecutive order, beginning with zero.
        </para>
    </refsect1>
    <refsect1 xml:id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>program</parameter> is not the name of a program object for which
            <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry> has been called in the past.
        </para>
    </refsect1>
    <refsect1 xml:id="notes"><title>Notes</title>
        <para>
            <function>glGetUniformBlockIndex</function> is available only if the GL version is 3.1 or greater.
        </para>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glGetActiveUniformBlockName</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glGetActiveUniformBlock</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>
        </para>
    </refsect1>
    <refsect1 xml:id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"/> 2010-2013 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>
