rename upstream-man-pages to upstream-doc

[clinton/guile-figl.git] / upstream-doc / manglsl / barrier.xml

<?xml version="1.0" encoding="UTF-8"?>\r
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"\r
              "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">\r
<refentry id="barrier">\r
    <refmeta>\r
        <refmetainfo>\r
            <copyright>\r
                <year>2011</year>\r
                <holder>Khronos Group</holder>\r
            </copyright>\r
        </refmetainfo>\r
        <refentrytitle>barrier</refentrytitle>\r
        <manvolnum>3G</manvolnum>\r
    </refmeta>\r
    <refnamediv>\r
        <refname>barrier</refname>\r
        <refpurpose>synchronize execution of multiple shader invocations</refpurpose>\r
    </refnamediv>\r
    <refsynopsisdiv><title>Declaration</title>\r
        <funcsynopsis>\r
            <funcprototype>\r
                <funcdef>void <function>barrier</function></funcdef>\r
                <paramdef>void</paramdef>\r
            </funcprototype>\r
        </funcsynopsis>\r
    </refsynopsisdiv>\r
    <refsect1 id="description"><title>Description</title>\r
        <para>\r
            <emphasis>Available only in the Tessellation Control and Compute Shaders</emphasis>, <function>barrier</function> provides\r
            a partially defined order of execution between shader invocations. For any given static instance of <function>barrier</function>,\r
            in a tessellation control shader, all invocations for a single input patch must enter it before any will be allowed\r
            to continue beyond it. For any given static instance of <function>barrier</function> in a compute shader, all invocations\r
            within a single work group must enter it before any are allowed to continue beyond it.\r
            This ensures that values written by one invocation prior to a given static instance\r
            of <function>barrier</function> can be safely read by other invocations after their call to the same static\r
            instance of <function>barrier</function>. Because invocations may execute in undefined order between these\r
            <function>barrier</function> calls, the values of a per-vertex or per-patch output variable, or any shared variable will be undefined\r
            in a number of cases.\r
        </para>\r
        <para>\r
            <function>barrier</function> may only be placed inside the function <code>main()</code> of the tessellation\r
            control shader, but may be placed anywhere in a compute shader. Calls to <function>barrier</function> may not\r
            be placed within any control flow. Barriers are also disallowed after a return\r
            statement in the function <code>main()</code>.\r
        </para>\r
    </refsect1>\r
    <refsect1 id="versions"><title>Version Support</title>\r
        <informaltable frame="topbot">\r
            #VARTABLECOLS#\r
                <thead>\r
                    #FUNCTABLEHEADER#\r
                    <row>\r
                        <entry>barrier</entry>#newin40#\r
                    </row>\r
                </thead>\r
            </tgroup>\r
        </informaltable>\r
    </refsect1>\r
    <refsect1 id="Copyright"><title>Copyright</title>\r
        <para>\r
            Copyright <trademark class="copyright"></trademark> 2011-2012 Khronos Group. \r
            This material may be distributed subject to the terms and conditions set forth in \r
            the Open Publication License, v 1.0, 8 June 1999.\r
            <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.\r
        </para>\r
    </refsect1>\r
</refentry>\r