<div class="refentry" id="gl_HelperInvocation">

<div class="titlepage"></div>

<div class="refnamediv">

<h2>Name</h2>

<p>gl_HelperInvocation — indicates whether a fragment shader invocation is a helper invocation</p>

</div>

<div class="refsynopsisdiv">

<h2>Declaration</h2>

<code class="fieldsynopsis"><span class="modifier">in </span><span class="type">bool </span><span class="varname">gl_HelperInvocation </span>;</code>

</div>

<div class="refsect1" id="description">

<h2>Description</h2>

<p>

The value <code class="varname">gl_HelperInvocation</code> is true if the

fragment shader invocation is considered a helper invocation and

is false otherwise. A helper invocation is a fragment-shader

invocation that is created solely for the purposes of evaluating

derivatives for use in non-helper fragment-shader invocations.

Such derivatives are computed implicitly in the built-in

function

<a class="citerefentry" href="texture"><span class="citerefentry"><span class="refentrytitle">texture</span></span></a>(),

and explicitly in the derivative functions

<a class="citerefentry" href="dFdx"><span class="citerefentry"><span class="refentrytitle">dFdx</span></span></a>()

and <code class="function">dFdy</code>.

</p>

<p>

Fragment shader helper invocations execute the same shader code

as non-helper invocations, but will not have side effects that

modify the framebuffer or other shader-accessible memory. In

particular:

</p>

<div class="itemizedlist">

<ul class="itemizedlist" style="list-style-type: disc; ">

<li class="listitem">

<p>

Fragments corresponding to helper invocations are

discarded when shader execution is complete, without

updating the framebuffer.

</p>

</li>

<li class="listitem">

<p>

Stores to image and buffer variables performed by

helper invocations have no effect on the underlying

image or buffer memory.

</p>

</li>

<li class="listitem">

<p>

Atomic operations to image, buffer, or atomic

counter variables performed by helper invocations

have no effect on the underlying image or buffer

memory. The values returned by such atomic

operations are undefined.

</p>

</li>

</ul>

</div>

<p>

</p>

<p>

Helper invocations may be generated for pixels not covered by a

primitive being rendered. While fragment shader inputs qualified

with centroid are normally required to be sampled in the

intersection of the pixel and the primitive, the requirement is

ignored for such pixels since there is no intersection between

the pixel and primitive.

</p>

<p>

Helper invocations may also be generated for fragments that are

covered by a primitive being rendered when the fragment is

killed by early fragment tests (using the early_fragment_tests

qualifier) or where the implementation is able to determine that

executing the fragment shader would have no effect other than

assisting in computing derivatives for other fragment shader

invocations.

</p>

<p>

The set of helper invocations generated when processing any set

of primitives is implementation dependent.

</p>

</div>

{$pipelinestall}{$examples}

<div class="refsect1" id="versions">

<h2>Version Support</h2>

<div class="informaltable">

<table style="border-collapse: collapse; border-top: 2px solid ; border-bottom: 2px solid ; border-left: 2px solid ; border-right: 2px solid ; ">

<colgroup>

<col style="text-align: left; "/>

<col style="text-align: center; " class="firstvers"/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; " class="lastvers"/>

</colgroup>

<thead>

<tr>

<th style="text-align: left; border-right: 2px solid ; ">

</th>

<th style="text-align: center; border-bottom: 2px solid ; " colspan="12">

<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>Variable 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>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>1.30</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>1.40</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>1.50</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>3.30</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>4.00</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<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 ; ">gl_HelperInvocation</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; 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="seealso">

<h2>See Also</h2>

<p>

<a class="citerefentry" href="dFdx"><span class="citerefentry"><span class="refentrytitle">dFdx</span></span></a>,

<a class="citerefentry" href="texture"><span class="citerefentry"><span class="refentrytitle">texture</span></span></a>

</p>

</div>

<div class="refsect1" id="Copyright">

<h2>Copyright</h2>

<p>

Copyright © 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="https://opencontent.org/openpub/" target="_top">https://opencontent.org/openpub/</a>.

</p>

</div>

</div>