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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glGetUniformLocation">
    <info>
        <copyright>
            <year>2003-2005</year>
            <holder>3Dlabs Inc. Ltd.</holder>
        </copyright>
        <copyright>
            <year>2010-2013</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>glGetUniformLocation</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glGetUniformLocation</refname>
        <refpurpose>Returns the location of a uniform variable</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
    <funcsynopsis>
        <funcprototype>
        <funcdef>GLint <function>glGetUniformLocation</function></funcdef>
        <paramdef>GLuint <parameter>program</parameter></paramdef>
        <paramdef>const 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>name</parameter></term>
        <listitem>
            <para>Points to a null terminated string containing
            the name of the uniform variable whose location is
            to be queried.</para>
        </listitem>
        </varlistentry>
    </variablelist>
    </refsect1>
    <refsect1 xml:id="description"><title>Description</title>
    <para><function>glGetUniformLocation </function> returns an
    integer that represents the location of a specific uniform
    variable within a program object. <parameter>name</parameter>
    must be a null terminated string that contains no white space.
    <parameter>name</parameter> must be an active uniform variable
    name in <parameter>program</parameter> that is not a structure,
    an array of structures, or a subcomponent of a vector or a
    matrix. This function returns -1 if <parameter>name</parameter>
    does not correspond to an active uniform variable in
    <parameter>program</parameter>, if <parameter>name</parameter>
    starts with the reserved prefix &quot;gl_&quot;, or if
    <parameter>name</parameter> is associated with an atomic counter or
    a named uniform block.</para>

    <para>Uniform variables that are structures or arrays of
    structures may be queried by calling
    <function>glGetUniformLocation</function> for each field within
    the structure. The array element operator &quot;[]&quot; and the
    structure field operator &quot;.&quot; may be used in
    <parameter>name</parameter> in order to select elements within
    an array or fields within a structure. The result of using these
    operators is not allowed to be another structure, an array of
    structures, or a subcomponent of a vector or a matrix. Except if
    the last part of <parameter>name</parameter> indicates a uniform
    variable array, the location of the first element of an array
    can be retrieved by using the name of the array, or by using the
    name appended by &quot;[0]&quot;.</para>

    <para>The actual locations assigned to uniform variables are not
    known until the program object is linked successfully. After
    linking has occurred, the command
    <function>glGetUniformLocation</function> can be used to obtain
    the location of a uniform variable. This location value can then
    be passed to
    <citerefentry><refentrytitle>glUniform</refentrytitle></citerefentry>
    to set the value of the uniform variable or to
    <citerefentry><refentrytitle>glGetUniform</refentrytitle></citerefentry>
    in order to query the current value of the uniform variable.
    After a program object has been linked successfully, the index
    values for uniform variables remain fixed until the next link
    command occurs. Uniform variable locations and values can only
    be queried after a link if the link was successful.</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_OPERATION</constant> is generated if
    <parameter>program</parameter> has not been successfully
    linked.</para>

    </refsect1>
    <refsect1 xml:id="associatedgets"><title>Associated Gets</title>
    <para><citerefentry><refentrytitle>glGetActiveUniform</refentrytitle></citerefentry>
    with arguments <parameter>program</parameter> and the index of
    an active uniform variable</para>

    <para><citerefentry><refentrytitle>glGetProgram</refentrytitle></citerefentry>
    with arguments <parameter>program</parameter> and
    <constant>GL_ACTIVE_UNIFORMS</constant> or
    <constant>GL_ACTIVE_UNIFORM_MAX_LENGTH</constant></para>

    <para><citerefentry><refentrytitle>glGetUniform</refentrytitle></citerefentry>
    with arguments <parameter>program</parameter> and the name of a
    uniform variable</para>
    <para><citerefentry><refentrytitle>glIsProgram</refentrytitle></citerefentry></para>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
    <para><citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
    <citerefentry><refentrytitle>glUniform</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"/> 2010-2013 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>
