upstream-man-pages/manglsl/barrier.xml

   1 <?xml version="1.0" encoding="UTF-8"?>
   2 <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
   3               "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
   4 <refentry id="barrier">
   5     <refmeta>
   6         <refmetainfo>
   7             <copyright>
   8                 <year>2011</year>
   9                 <holder>Khronos Group</holder>
  10             </copyright>
  11         </refmetainfo>
  12         <refentrytitle>barrier</refentrytitle>
  13         <manvolnum>3G</manvolnum>
  14     </refmeta>
  15     <refnamediv>
  16         <refname>barrier</refname>
  17         <refpurpose>synchronize execution of multiple shader invocations</refpurpose>
  18     </refnamediv>
  19     <refsynopsisdiv><title>Declaration</title>
  20         <funcsynopsis>
  21             <funcprototype>
  22                 <funcdef>void <function>barrier</function></funcdef>
  23                 <paramdef>void</paramdef>
  24             </funcprototype>
  25         </funcsynopsis>
  26     </refsynopsisdiv>
  27     <refsect1 id="description"><title>Description</title>
  28         <para>
  29             <emphasis>Available only in the Tessellation Control and Compute Shaders</emphasis>, <function>barrier</function> provides
  30             a partially defined order of execution between shader invocations. For any given static instance of <function>barrier</function>,
  31             in a tessellation control shader, all invocations for a single input patch must enter it before any will be allowed
  32             to continue beyond it. For any given static instance of <function>barrier</function> in a compute shader, all invocations
  33             within a single work group must enter it before any are allowed to continue beyond it.
  34             This ensures that values written by one invocation prior to a given static instance
  35             of <function>barrier</function> can be safely read by other invocations after their call to the same static
  36             instance of <function>barrier</function>. Because invocations may execute in undefined order between these
  37             <function>barrier</function> calls, the values of a per-vertex or per-patch output variable, or any shared variable will be undefined
  38             in a number of cases.
  39         </para>
  40         <para>
  41             <function>barrier</function> may only be placed inside the function <code>main()</code> of the tessellation
  42             control shader, but may be placed anywhere in a compute shader. Calls to <function>barrier</function> may not
  43             be placed within any control flow. Barriers are also disallowed after a return
  44             statement in the function <code>main()</code>.
  45         </para>
  46     </refsect1>
  47     <refsect1 id="versions"><title>Version Support</title>
  48         <informaltable frame="topbot">
  49             #VARTABLECOLS#
  50                 <thead>
  51                     #FUNCTABLEHEADER#
  52                     <row>
  53                         <entry>barrier</entry>#newin40#
  54                     </row>
  55                 </thead>
  56             </tgroup>
  57         </informaltable>
  58     </refsect1>
  59     <refsect1 id="Copyright"><title>Copyright</title>
  60         <para>
  61             Copyright <trademark class="copyright"></trademark> 2011-2012 Khronos Group.
  62             This material may be distributed subject to the terms and conditions set forth in
  63             the Open Publication License, v 1.0, 8 June 1999.
  64             <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
  65         </para>
  66     </refsect1>
  67 </refentry>