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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="gl_SampleMask">
    <info>
        <copyright>
            <year>2011-2013</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>gl_SampleMask</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>gl_SampleMask</refname>
        <refpurpose>specifies the sample coverage mask for the current fragment</refpurpose>
    </refnamediv>
    <refsynopsisdiv>
        <title>Declaration</title>
        <fieldsynopsis>
            <modifier>out</modifier>
            <type>int</type>
            <varname>gl_SampleMask[]</varname>
        </fieldsynopsis>
    </refsynopsisdiv>
    <refsect1 xml:id="description"><title>Description</title>
        <para>
            <varname>gl_SampleMask</varname> is a fragment language output array that may be
            used to set the sample mask for the fragment being processed. Coverage for the current
            fragment will become the logical AND of the coverage mask and the output <varname>gl_SampleMask</varname>.
            That is, setting a bit in <varname>gl_SampleMask</varname> to zero will cause the
            corresponding sample to be considered uncovered for the purposes of multisample fragment operations. However,
            setting sample mask bits back to one will never enable samples not covered by the original primitive.
            Bit <emphasis>B</emphasis> of mask <varname>gl_SampleMask[M]</varname> corresponds to sample
            32 * <emphasis>M</emphasis> + <emphasis>B</emphasis>. This array must be sized in the fragment shader
            either implicitly or explicitly to be the same size as the implementation-dependent maximum
            sample-mask (as an array of 32-bit elements), determined by the maximum number of samples.
            If the fragment shader statically assigns a value to <varname>gl_SampleMask</varname>, the
            sample mask will be undefined for any array elements of any fragment shader invocation that
            fails to assign a value. If a shader does not statically assign a value to <varname>gl_SampleMask</varname>,
            the sample mask has no effect on the processing of a fragment.
            If the fragment shader is being evaluated at any  frequency other than per-fragment, bits within
            the sample mask not corresponding to the current fragment shader invocation are ignored.
        </para>
    </refsect1>
    <refsect1 xml:id="versions"><title>Version Support</title>
        <informaltable>
            <tgroup cols="11" align="left">
                <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="varhead.xml" xpointer="xpointer(/*/*)"/>
                <tbody>
                    <row>
                        <entry>gl_SampleMask</entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="version.xml" xpointer="xpointer(/*/*[@role='40']/*)"/>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>gl_SampleMaskIn</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>gl_SampleID</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>gl_SamplePosition</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>gl_FragCoord</refentrytitle></citerefentry>
        </para>
    </refsect1>
    <refsect1 xml:id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"/> 2011-2013 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>
