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<refentry id="glGetProgramInterface">
    <refmeta>
        <refmetainfo>
            <copyright>
                <year>2012</year>
                <holder>Khronos Group</holder>
            </copyright>
        </refmetainfo>
        <refentrytitle>glGetProgramInterface</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glGetProgramInterface</refname>
        <refpurpose>query a property of an interface in a program</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glGetProgramInterfaceiv</function></funcdef>
                <paramdef>GLuint <parameter>program</parameter></paramdef>
                <paramdef>GLenum <parameter>programInterface</parameter></paramdef>
                <paramdef>GLenum <parameter>pname</parameter></paramdef>
                <paramdef>GLint * <parameter>params</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>program</parameter></term>
            <listitem>
                <para>
                    The name of a program object whose interface to query.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>programInterface</parameter></term>
            <listitem>
                <para>
                    A token identifying the interface within <parameter>program</parameter> to query.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>pname</parameter></term>
            <listitem>
                <para>
                    The name of the parameter within <parameter>programInterface</parameter> to query.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>params</parameter></term>
            <listitem>
                <para>
                    The address of a variable to retrieve the value of <parameter>pname</parameter> for the program interface.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
        <para>
            <function>glGetProgramInterfaceiv</function> queries the property of the interface identifed
            by <parameter>programInterface</parameter> in <parameter>program</parameter>, the property name of
            which is given by <parameter>pname</parameter>.
        </para>
        <para>
            <parameter>program</parameter> must be the name of an existing program object. <parameter>programInterface</parameter>
            is the name of the interface within <parameter>program</parameter> to query and must be one of the following
            values:
        </para>
        <variablelist>
            <varlistentry>
                <term><constant>GL_UNIFORM</constant></term>
                <listitem>
                    <para>
                        The query is targeted at the set of active uniforms within <parameter>program</parameter>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_UNIFORM_BLOCK</constant></term>
                <listitem>
                    <para>
                        The query is targeted at the set of active uniform blocks within <parameter>program</parameter>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_ATOMIC_COUNTER_BUFFER</constant></term>
                <listitem>
                    <para>
                        The query is targeted at the set of active atomic counter buffer binding points within <parameter>program</parameter>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_PROGRAM_INPUT</constant></term>
                <listitem>
                    <para>
                        The query is targeted at the set of active input variables used by the first shader stage of <parameter>program</parameter>.
                        If <parameter>program</parameter> contains multiple shader stages then input variables from any stage other than the first
                        will not be enumerated.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_PROGRAM_OUTPUT</constant></term>
                <listitem>
                    <para>
                        The query is targeted at the set of active output variables produced by the last shader stage of <parameter>program</parameter>.
                        If <parameter>program</parameter> contains multiple shader stages then output variables from any stage other than the last
                        will not be enumerated.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_VERTEX_SUBROUTINE</constant></term>,
                <term><constant>GL_TESS_CONTROL_SUBROUTINE</constant></term>,
                <term><constant>GL_TESS_EVALUATION_SUBROUTINE</constant></term>,
                <term><constant>GL_GEOMETRY_SUBROUTINE</constant></term>,
                <term><constant>GL_FRAGMENT_SUBROUTINE</constant></term>,
                <term><constant>GL_COMPUTE_SUBROUTINE</constant></term>
                <listitem>
                    <para>
                        The query is targeted at the set of active subroutines for the vertex, tessellation control, tessellation evaluation,
                        geometry, fragment and compute shader stages of <parameter>program</parameter>, respectively.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_VERTEX_SUBROUTINE_UNIFORM</constant></term>,
                <term><constant>GL_TESS_CONTROL_SUBROUTINE_UNIFORM</constant></term>,
                <term><constant>GL_TESS_EVALUATION_SUBROUTINE_UNIFORM</constant></term>,
                <term><constant>GL_GEOMETRY_SUBROUTINE_UNIFORM</constant></term>,
                <term><constant>GL_FRAGMENT_SUBROUTINE_UNIFORM</constant></term>,
                <term><constant>GL_COMPUTE_SUBROUTINE_UNIFORM</constant></term>
                <listitem>
                    <para>
                        The query is targeted at the set of active subroutine uniform variables used by the vertex, tessellation control, tessellation evaluation,
                        geometry, fragment and compute shader stages of <parameter>program</parameter>, respectively.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_TRANSFORM_FEEDBACK_VARYING</constant></term>
                <listitem>
                    <para>
                        The query is targeted at the set of output variables from the last non-fragment stage of <parameter>program</parameter> that would be
                        captured if transform feedback were active.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_BUFFER_VARIABLE</constant></term>
                <listitem>
                    <para>
                        The query is targeted at the set of active buffer variables used by <parameter>program</parameter>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_SHADER_STORAGE_BLOCK</constant></term>
                <listitem>
                    <para>
                        The query is targeted at the set of active shader storage blocks used by <parameter>program</parameter>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_TRANSFORM_FEEDBACK_BUFFER</constant></term>
                <listitem>
                    <para>
                        The query is targeted at the set of active buffer binding points to which output variables in the
                        <constant>GL_TRANSFORM_FEEDBACK_VARYING</constant> interface are written.
                    </para>
                </listitem>
            </varlistentry>
        </variablelist>
        <para>
            <parameter>pname</parameter> identifies the property of <parameter>programInterface</parameter>
            to return in <parameter>params</parameter>.
        </para>
        <para>
            If <parameter>pname</parameter> is <constant>GL_ACTIVE_RESOURCES</constant>, the value returned is the number of
            resources in the active resource list for <parameter>programInterface</parameter>.  If the list
            of active resources for <parameter>programInterface</parameter> is empty, zero is returned.
        </para>
        <para>
            If <parameter>pname</parameter> is <constant>GL_MAX_NAME_LENGTH</constant>, the value returned is the length of the
            longest active name string for an active resource in <parameter>programInterface</parameter>.
            This length includes an extra character for the null terminator.  If the
            list of active resources for <parameter>programInterface</parameter> is empty, zero is
            returned.  It is an error to specify <constant>GL_MAX_NAME_LENGTH</constant> when <parameter>programInterface</parameter>
            is <constant>GL_ATOMIC_COUNTER_BUFFER</constant>, as active atomic counter buffer resources are
            not assigned name strings.
        </para>
        <para>
            If <parameter>pname</parameter> is <constant>GL_MAX_NUM_ACTIVE_VARIABLES</constant>, the value returned is the number
            of active variables belonging to the interface block or atomic counter
            buffer resource in <parameter>programInterface</parameter> with the most active variables.  If
            the list of active resources for <parameter>programInterface</parameter> is empty, zero is
            returned.  When <parameter>pname</parameter> is <constant>GL_MAX_NUM_ACTIVE_VARIABLES</constant>, <parameter>programInterface</parameter>
            must be <constant>GL_UNIFORM_BLOCK</constant>, <constant>GL_ATOMIC_COUNTER_BUFFER</constant>, or <constant>GL_SHADER_STORAGE_BLOCK</constant>.
        </para>
        <para>
            If <parameter>pname</parameter> is <constant>GL_MAX_NUM_COMPATIBLE_SUBROUTINES</constant>, the value returned is the
            number of compatible subroutines belonging to the active subroutine
            uniform in <parameter>programInterface</parameter> with the most compatible subroutines.  If
            the list of active resources for <parameter>programInterface</parameter> is empty, zero is
            returned. When <parameter>pname</parameter> is <constant>GL_MAX_NUM_COMPATIBLE_SUBROUTINES</constant>,
            <parameter>programInterface</parameter> must be one of <constant>GL_VERTEX_SUBROUTINE_UNIFORM</constant>,
            <constant>GL_TESS_CONTROL_SUBROUTINE_UNIFORM</constant>, <constant>GL_TESS_EVALUATION_SUBROUTINE_UNIFORM</constant>,
            <constant>GL_GEOMETRY_SUBROUTINE_UNIFORM</constant>, <constant>GL_FRAGMENT_SUBROUTINE_UNIFORM</constant>, or
            <constant>GL_COMPUTE_SUBROUTINE_UNIFORM</constant>.
        </para>
    </refsect1>
    <refsect1 id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if <parameter>identifier</parameter>
            is not one of the accepted object types.
        </para>
        <para>
            <constant>GL_INVALID_VALUE</constant> is generated if <parameter>program</parameter>
            is not the name of an existing sync object.
        </para>
        <para>
            <constant>GL_INVALID_VALUE</constant> is generated if <parameter>bufSize</parameter> is
            zero.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>pname</parameter> is <constant>GL_MAX_NAME_LENGTH</constant> and
            <parameter>programInterface</parameter> is <constant>GL_ATOMIC_COUNTER_BUFFER</constant> or <constant>GL_TRANSFORM_FEEDBACK_BUFFER</constant>,
            since active atomic counter and transform feedback buffer resources are not assigned name strings.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> error is generated if <parameter>pname</parameter> is
            <constant>GL_MAX_NUM_ACTIVE_VARIABLES</constant> and <parameter>programInterface</parameter> is not <constant>GL_UNIFORM_BLOCK</constant>,
            <constant>GL_SHADER_STORAGE_BLOCK</constant>, <constant>GL_ATOMIC_COUNTER_BUFFER</constant>, or
            <constant>GL_TRANSFORM_FEEDBACK_BUFFER</constant>.
        </para>
        <para>
            If not NULL, <parameter>length</parameter> and <parameter>label</parameter> should be addresses
            to which the client has write access, otherwise undefined behavior, including process termination
            may occur.
        </para>
    </refsect1>
    <refsect1 id="associatedgets"><title>Associated Gets</title>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_MAX_LABEL_LENGTH</constant>.
        </para>
    </refsect1>
    <refsect1 id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glPushDebugGroup</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glPopDebugGroup</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glObjectLabel</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glGetObjectLabel</refentrytitle></citerefentry>.
        </para>
    </refsect1>
    <refsect1 id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"></trademark> 2012 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.
            <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
        </para>
    </refsect1>
</refentry>
