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<title>barrier - OpenGL 4 Reference Pages</title>
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<div class="refentry" id="barrier">
<div class="titlepage"/>
<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">
<table style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">
<tr>
<td>
<code class="funcdef">void <strong class="fsfunc">barrier</strong>(</code>
</td>
<td>void<code>)</code>;</td>
</tr>
</table>
<div class="funcprototype-spacer"> </div>
</div>
</div>
<div class="refsect1" id="description">
<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" id="versions">
<h2>Version Support</h2>
<div class="informaltable">
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<span class="bold"><strong>OpenGL Shading Language Version</strong></span>
</th>
</tr>
<tr>
<th style="text-align: left; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>Function Name</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>1.10</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>1.20</strong></span>
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<span class="bold"><strong>1.30</strong></span>
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<span class="bold"><strong>1.40</strong></span>
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<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>1.50</strong></span>
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<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>3.30</strong></span>
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<span class="bold"><strong>4.00</strong></span>
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<span class="bold"><strong>4.10</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.20</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.30</strong></span>
</th>
<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.40</strong></span>
</th>
<th style="text-align: center; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.50</strong></span>
</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align: left; border-right: 2px solid ; ">barrier</td>
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<td style="text-align: center; border-right: 2px solid ; ">-</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; ">✔</td>
<td style="text-align: center; ">✔</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="refsect1" id="Copyright">
<h2>Copyright</h2>
<p>
Copyright <span class="trademark"/>© 2011-2014 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 class="link" href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
</p>
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