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<?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" pref:renderer="mathplayer-dl"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><link rel="stylesheet" type="text/css" href="opengl-man.css" /><title>barrier - OpenGL Shading Language (GLSL)</title><meta name="generator" content="DocBook XSL Stylesheets V1.69.1" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="barrier"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>barrier — synchronize execution of multiple shader invocations</p></div><div class="refsynopsisdiv"><h2>Declaration</h2><div class="funcsynopsis"><p><code class="funcdef">void <b class="fsfunc">barrier</b>(</code>void<code>)</code>;</p></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
            <span class="emphasis"><em>Available only in the Tessellation Control and Compute Shaders</em></span>, <code class="function">barrier</code> provides
            a partially defined order of execution between shader invocations. For any given static instance of <code class="function">barrier</code>,
            in a tessellation control shader, all invocations for a single input patch must enter it before any will be allowed
            to continue beyond it. For any given static instance of <code class="function">barrier</code> in a compute shader, all invocations
            within a single work group must enter it before any are allowed to continue beyond it.
            This ensures that values written by one invocation prior to a given static instance
            of <code class="function">barrier</code> can be safely read by other invocations after their call to the same static
            instance of <code class="function">barrier</code>. Because invocations may execute in undefined order between these
            <code class="function">barrier</code> calls, the values of a per-vertex or per-patch output variable, or any shared variable will be undefined
            in a number of cases.
        </p><p>
            <code class="function">barrier</code> may only be placed inside the function <code class="code">main()</code> of the tessellation
            control shader, but may be placed anywhere in a compute shader. Calls to <code class="function">barrier</code> may not
            be placed within any control flow. Barriers are also disallowed after a return
            statement in the function <code class="code">main()</code>.
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="versions"></a><h2>Version Support</h2><div class="informaltable"><table border="1"><colgroup><col align="left" /><col align="center" /><col align="center" /><col align="center" /><col align="center" /><col align="center" /><col align="center" /><col align="center" /><col align="center" /><col align="center" /><col align="center" /></colgroup><thead><tr><th align="left"><span class="bold"><strong>Function</strong></span></th><th align="left"><span class="bold"><strong>Version 1.10</strong></span></th><th align="left"><span class="bold"><strong>Version 1.20</strong></span></th><th align="left"><span class="bold"><strong>Version 1.30</strong></span></th><th align="left"><span class="bold"><strong>Version 1.40</strong></span></th><th align="left"><span class="bold"><strong>Version 1.50</strong></span></th><th align="left"><span class="bold"><strong>Version 3.30</strong></span></th><th align="left"><span class="bold"><strong>Version 4.00</strong></span></th><th align="left"><span class="bold"><strong>Version 4.10</strong></span></th><th align="left"><span class="bold"><strong>Version 4.20</strong></span></th><th align="center"><span class="bold"><strong>Version 4.30</strong></span></th></tr><tr><th align="left">barrier</th><th align="center"><span class="emphasis"><em>-</em></span></th><th align="center"><span class="emphasis"><em>-</em></span></th><th align="center"><span class="emphasis"><em>-</em></span></th><th align="center"><span class="emphasis"><em>-</em></span></th><th align="center"><span class="emphasis"><em>-</em></span></th><th align="center"><span class="emphasis"><em>-</em></span></th><th align="center"><span class="emphasis"><em>Y</em></span></th><th align="center"><span class="emphasis"><em>Y</em></span></th><th align="center"><span class="emphasis"><em>Y</em></span></th><th align="center"><span class="emphasis"><em>Y</em></span></th></tr></thead></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
            Copyright <span class="trademark"></span>© 2011-2012 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.
            <a href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
        </p></div></div></body></html>
