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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glGetUniform">
    <info>
        <copyright>
            <year>2003-2005</year>
            <holder>3Dlabs Inc. Ltd.</holder>
        </copyright>
        <copyright>
            <year>2010-2015</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>glGetUniform</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refdescriptor>glGetUniform</refdescriptor>
        <refname>glGetUniformfv</refname>
        <refname>glGetUniformiv</refname>
        <refname>glGetUniformuiv</refname>
        <refname>glGetnUniformfv</refname>
        <refname>glGetnUniformiv</refname>
        <refname>glGetnUniformuiv</refname>
        <refpurpose>Returns the value of a uniform variable</refpurpose>
    </refnamediv>
    <refsynopsisdiv>
        <title>C Specification</title>
    <funcsynopsis>
        <funcprototype>
        <funcdef>void <function>glGetUniformfv</function></funcdef>
        <paramdef>GLuint <parameter>program</parameter></paramdef>
        <paramdef>GLint <parameter>location</parameter></paramdef>
        <paramdef>GLfloat *<parameter>params</parameter></paramdef>
        </funcprototype>
        <funcprototype>
        <funcdef>void <function>glGetUniformiv</function></funcdef>
        <paramdef>GLuint <parameter>program</parameter></paramdef>
        <paramdef>GLint <parameter>location</parameter></paramdef>
        <paramdef>GLint *<parameter>params</parameter></paramdef>
        </funcprototype>
        <funcprototype>
        <funcdef>void <function>glGetUniformuiv</function></funcdef>
        <paramdef>GLuint <parameter>program</parameter></paramdef>
        <paramdef>GLint <parameter>location</parameter></paramdef>
        <paramdef>GLuint *<parameter>params</parameter></paramdef>
        </funcprototype>
      <funcprototype>
        <funcdef>void <function>glGetnUniformfv</function></funcdef>
        <paramdef>GLuint <parameter>program</parameter></paramdef>
        <paramdef>GLint <parameter>location</parameter></paramdef>
        <paramdef>GLsizei <parameter>bufSize</parameter></paramdef>
        <paramdef>GLfloat *<parameter>params</parameter></paramdef>
      </funcprototype>
      <funcprototype>
        <funcdef>void <function>glGetnUniformiv</function></funcdef>
        <paramdef>GLuint <parameter>program</parameter></paramdef>
        <paramdef>GLint <parameter>location</parameter></paramdef>
        <paramdef>GLsizei <parameter>bufSize</parameter></paramdef>
        <paramdef>GLint *<parameter>params</parameter></paramdef>
      </funcprototype>
      <funcprototype>
        <funcdef>void <function>glGetnUniformuiv</function></funcdef>
        <paramdef>GLuint <parameter>program</parameter></paramdef>
        <paramdef>GLint <parameter>location</parameter></paramdef>
        <paramdef>GLsizei <parameter>bufSize</parameter></paramdef>
        <paramdef>GLuint *<parameter>params</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>location</parameter></term>
        <listitem>
            <para>Specifies the location of the uniform variable
            to be queried.</para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>bufSize</parameter></term>
        <listitem>
            <para>Specifies the size of the buffer
            <parameter>params</parameter>.
            </para>
        </listitem>
        </varlistentry>
        <varlistentry>
        <term><parameter>params</parameter></term>
        <listitem>
            <para>Returns the value of the specified uniform
            variable.</para>
        </listitem>
        </varlistentry>
    </variablelist>
    </refsect1>
    <refsect1 xml:id="description"><title>Description</title>
    <para><function>glGetUniform</function> and <function>glGetnUniform</function> return in
    <parameter>params</parameter> the value(s) of the specified
    uniform variable. The type of the uniform variable specified by
    <parameter>location</parameter> determines the number of values
    returned. If the uniform variable is defined in the shader as a
    boolean, int, unsigned int, or float, a single value will be returned. If it
    is defined as a vec2, ivec2, uvec2, or bvec2, two values will be
    returned. If it is defined as a vec3, ivec3, uvec3, or bvec3, three
    values will be returned, and so on. To query values stored in
    uniform variables declared as arrays, call
    <function>glGetUniform</function> for each element of the array.
    To query values stored in uniform variables declared as
    structures, call <function>glGetUniform</function> for each
    field in the structure. The values for uniform variables
    declared as a matrix will be returned in column major
    order.</para>

    <para>The locations assigned to uniform variables are not known
    until the program object is linked. After linking has occurred,
    the command
    <citerefentry><refentrytitle>glGetUniformLocation</refentrytitle></citerefentry>
    can be used to obtain the location of a uniform variable. This
    location value can then be passed to
    <function>glGetUniform</function> or <function>glGentUniform</function> 
    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. The uniform
    variable values can only be queried after a link if the link was
    successful.</para>
    <para>
        The only difference between <function>glGetUniform</function> and
        <function>glGetnUniform</function> is that
        <function>glGetnUniform</function> will generate an error if size of the
        <parameter>params</parameter> buffer, as described by
        <parameter>bufSize</parameter>, is not large enough to hold the result
        data.
    </para>
    </refsect1>
    <refsect1 xml:id="notes"><title>Notes</title>
    <para>If an error is generated, no change is made to the
    contents of <parameter>params</parameter>.</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>

    <para><constant>GL_INVALID_OPERATION</constant> is generated if
    <parameter>location</parameter> does not correspond to a valid
    uniform variable location for the specified program object.</para>
    
    <para><constant>GL_INVALID_OPERATION</constant> is generated by
    <function>glGetnUniform</function> if the buffer size required to store
    the requested data is greater than <parameter>bufSize</parameter>.</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>glGetProgramiv</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>glGetUniformLocation</refentrytitle></citerefentry>
    with arguments <parameter>program</parameter> and the name of a
    uniform variable</para>
    </refsect1>
    <refsect1 xml:id="versions">
        <title>API Version Support</title>
        <informaltable>
            <tgroup cols="5" align="left">
                <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
                <tbody>
                    <row>
                        <entry><function>glGetUniformfv</function></entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es20']/*)"/>
                    </row>
                    <row>
                        <entry><function>glGetUniformiv</function></entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es20']/*)"/>
                    </row>
                    <row>
                        <entry><function>glGetUniformuiv</function></entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es30']/*)"/>
                    </row>
                    <row>
                        <entry><function>glGetnUniformfv</function></entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es32']/*)"/>
                    </row>
                    <row>
                        <entry><function>glGetnUniformiv</function></entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es32']/*)"/>
                    </row>
                    <row>
                        <entry><function>glGetnUniformuiv</function></entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es32']/*)"/>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
        <para><citerefentry><refentrytitle>glCreateProgram</refentrytitle></citerefentry>,
        <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"/> 2010-2015 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>
