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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glEnable">
    <info>
        <copyright>
            <year>1991-2006</year>
            <holder>Silicon Graphics, Inc.</holder>
        </copyright>
        <copyright>
            <year>2010-2014</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>glEnable</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glEnable</refname>
        <refpurpose>enable or disable server-side GL capabilities</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glEnable</function></funcdef>
                <paramdef>GLenum <parameter>cap</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glDisable</function></funcdef>
                <paramdef>GLenum <parameter>cap</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 xml:id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>cap</parameter></term>
            <listitem>
                <para>
                    Specifies a symbolic constant indicating a GL capability.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 xml:id="description"><title>Description</title>
        <para>
            <function>glEnable</function> and
            <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry>
            enable and disable various capabilities. Use
            <citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry>
            or
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
            to determine the current setting of any capability. The initial
            value for each capability with the exception of
            <constant>GL_DITHER</constant> is <constant>GL_FALSE</constant>.
            The initial value for <constant>GL_DITHER</constant> is
            <constant>GL_TRUE</constant>.
        </para>
        <para>
            Both <function>glEnable</function> and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> take a single argument, <parameter>cap</parameter>,
            which can assume one of the following values:
        </para>
        <variablelist>
            <varlistentry>
                <term><constant>GL_BLEND</constant></term>
                <listitem>
                    <para>
                        If enabled,
                        blend the computed fragment color values with the values in the color
                        buffers. See <citerefentry><refentrytitle>glBlendFunc</refentrytitle></citerefentry>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_CULL_FACE</constant></term>
                <listitem>
                <para>
                </para>
                    <para>
                        If enabled,
                        cull polygons based on their winding in window coordinates.
                        See <citerefentry><refentrytitle>glCullFace</refentrytitle></citerefentry>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_DEPTH_TEST</constant></term>
                <listitem>
                    <para>
                        If enabled,
                        do depth comparisons and update the depth buffer. Note that even if
                        the depth buffer exists and the depth mask is non-zero, the
                        depth buffer is not updated if the depth test is disabled. See
                        <citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry> and
                        <citerefentry><refentrytitle>glDepthRangef</refentrytitle></citerefentry>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_DITHER</constant>    </term>
                <listitem>
                    <para>
                        If enabled,
                        dither color components or indices before they are written to the
                        color buffer.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_POLYGON_OFFSET_FILL</constant></term>
                <listitem>
                    <para>
                        If enabled, an offset is added to depth values of a polygon's
                        fragments before the depth comparison is performed.
                        See <citerefentry><refentrytitle>glPolygonOffset</refentrytitle></citerefentry>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_PRIMITIVE_RESTART_FIXED_INDEX</constant></term>
                <listitem>
                    <para>
                        Enables primitive restarting.  If enabled, any one of the draw commands
                        which transfers a set of generic attribute array elements to the GL will restart
                        the primitive when the index of the vertex is equal to
                        <inlineequation>
                            <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                                <mml:msup>
                                    <mml:mn>2</mml:mn>
                                    <mml:mi>n</mml:mi>
                                </mml:msup>
                                <mml:mo>&minus;</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:math>
                        </inlineequation>
                        where <emphasis>n</emphasis> is 8, 16 or 32 if the type is
                        <constant>GL_UNSIGNED_BYTE</constant>,
                        <constant>GL_UNSIGNED_SHORT</constant>, or
                        <constant>GL_UNSIGNED_INT</constant>, respectively.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_RASTERIZER_DISCARD</constant></term>
                <listitem>
                    <para>
                        If enabled, primitives are discarded immediately before the rasterization stage,
                        but after the optional transform feedback stage.
                        <citerefentry><refentrytitle>glClear</refentrytitle></citerefentry> and
                        <citerefentry><refentrytitle>glClearBuffer</refentrytitle></citerefentry>* commands
                        are also ignored.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_SAMPLE_ALPHA_TO_COVERAGE</constant></term>
                <listitem>
                    <para>
                        If enabled,
                        compute a temporary coverage value where each bit is determined by the
                        alpha value at the corresponding sample location.  The temporary coverage
                        value is then ANDed with the fragment coverage value.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_SAMPLE_COVERAGE</constant></term>
                <listitem>
                    <para>
                        If enabled,
                        the fragment's coverage is ANDed with the temporary coverage value.  If
                        <constant>GL_SAMPLE_COVERAGE_INVERT</constant> is set to <constant>GL_TRUE</constant>, invert the coverage
                        value.
                        See <citerefentry><refentrytitle>glSampleCoverage</refentrytitle></citerefentry>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_SCISSOR_TEST</constant></term>
                <listitem>
                    <para>
                        If enabled,
                        discard fragments that are outside the scissor rectangle.
                        See <citerefentry><refentrytitle>glScissor</refentrytitle></citerefentry>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_STENCIL_TEST</constant></term>
                <listitem>
                    <para>
                        If enabled,
                        do stencil testing and update the stencil buffer.
                        See <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry>.
                    </para>
                </listitem>
            </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 xml:id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if <parameter>cap</parameter> is not one of the values
            listed previously.
        </para>
    </refsect1>
    <refsect1 xml:id="associatedgets"><title>Associated Gets</title>
        <para>
            <citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry>
        </para>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
        </para>
    </refsect1>
    <refsect1 xml:id="versions">
        <title>API Version Support</title>
        <informaltable>
            <tgroup cols="3" align="left">
                <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
                <tbody>
                    <row>
                        <entry><function>glEnable</function></entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es20']/*)"/>
                    </row>
                    <row>
                        <entry><function>glDisable</function></entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es20']/*)"/>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glBlendFunc</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glCullFace</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glDepthFunc</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glDepthRangef</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glPolygonOffset</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glSampleCoverage</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glScissor</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glStencilFunc</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glStencilOp</refentrytitle></citerefentry>,
        </para>
    </refsect1>
    <refsect1 xml:id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"/> 1991-2006 Silicon Graphics, Inc.
            Copyright <trademark class="copyright"/> 2010-2014 Khronos Group.
            This document is licensed under the SGI Free Software B License.
            For details, see
            <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</link>.
        </para>
    </refsect1>
</refentry>
