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<refentry id="glGetUniformLocation">
    <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 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 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> or if <parameter>name</parameter>
	starts with the reserved prefix &quot;gl_&quot;.</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 id="notes"><title>Notes</title>
	<para><function>glGetUniformLocation</function> is available
	only if the GL version is 2.0 or greater.</para>
    </refsect1>
    <refsect1 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>

	<para><constant>GL_INVALID_OPERATION</constant> is generated if
	<function>glGetUniformLocation</function> is executed between
	the execution of
	<citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
	and the corresponding execution of
	<citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.</para>
    </refsect1>
    <refsect1 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 id="seealso"><title>See Also</title>
	<para><citerefentry><refentrytitle>glLinkProgram</refentrytitle></citerefentry>,
	<citerefentry><refentrytitle>glUniform</refentrytitle></citerefentry></para>
    </refsect1>
    <refsect1 id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"></trademark> 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.
            <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
        </para>
    </refsect1>
</refentry>
