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<title>gl_SampleID - OpenGL 4 Reference Pages</title>
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<div class="refentry" id="gl_SampleID">
<div class="titlepage"/>
<div class="refnamediv">
<h2>Name</h2>
<p>gl_SampleID — contains the index of the sample currently being processed</p>
</div>
<div class="refsynopsisdiv">
<h2>Declaration</h2>
<code class="fieldsynopsis"><span class="modifier">in </span><span class="type">int </span><span class="varname">gl_SampleID </span>;</code>
</div>
<div class="refsect1" id="description">
<h2>Description</h2>
<p>
<code class="varname">gl_SampleID</code> is a fragment language input variable that contains
the index of the sample currently being processed. This variable is in the range
0 to <a class="citerefentry" href="gl_NumSamples.xhtml"><span class="citerefentry"><span class="refentrytitle">gl_NumSamples</span></span></a> - 1, where
<a class="citerefentry" href="gl_NumSamples.xhtml"><span class="citerefentry"><span class="refentrytitle">gl_NumSamples</span></span></a>
is the total number of samples in each fragment for the current framebuffer (and thus 1 if
rendering to a non-multisample buffer). Any static use of this variable in a fragment
shader causes the entire shader to be evaluated per-sample rather than per-fragment.
</p>
<p>
When rendering to a non-multisample buffer, or if multisample rasterization is disabled,
<code class="varname">gl_SampleID</code> will always be zero. <a class="citerefentry" href="gl_NumSamples.xhtml"><span class="citerefentry"><span class="refentrytitle">gl_NumSamples</span></span></a>
is the sample count of the framebuffer regardless of whether multisample rasterization is
enabled or not.
</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>
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<span class="bold"><strong>Variable Name</strong></span>
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<span class="bold"><strong>1.10</strong></span>
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<span class="bold"><strong>1.20</strong></span>
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<span class="bold"><strong>1.50</strong></span>
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<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>
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<span class="bold"><strong>4.20</strong></span>
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<span class="bold"><strong>4.30</strong></span>
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<span class="bold"><strong>4.40</strong></span>
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<span class="bold"><strong>4.50</strong></span>
</th>
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</thead>
<tbody>
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<td style="text-align: left; border-right: 2px solid ; ">gl_SampleID</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; ">✔</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="refsect1" id="seealso">
<h2>See Also</h2>
<p>
<a class="citerefentry" href="gl_SamplePosition.xhtml"><span class="citerefentry"><span class="refentrytitle">gl_SamplePosition</span></span></a>,
<a class="citerefentry" href="gl_NumSamples.xhtml"><span class="citerefentry"><span class="refentrytitle">gl_NumSamples</span></span></a>
</p>
</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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