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<head>
<title>gl_PrimitiveID - OpenGL 4 Reference Pages</title>
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<div class="refentry" id="gl_PrimitiveID">
<div class="titlepage"/>
<div class="refnamediv">
<h2>Name</h2>
<p>gl_PrimitiveID — contains the index of the current primitive</p>
</div>
<div class="refsynopsisdiv">
<h2>Declaration</h2>
<p>
</p>
<pre class="programlisting">// In tessellation control, tessellation evaluation, and
// fragment shaders</pre>
<p>
<code class="fieldsynopsis"><span class="modifier">in </span><span class="type">int </span><span class="varname">gl_PrimitiveID </span>;</code>
</p>
<p>
</p>
<pre class="programlisting">// In geometry shaders</pre>
<p>
<code class="fieldsynopsis"><span class="modifier">out </span><span class="type">int </span><span class="varname">gl_PrimitiveID </span>;</code>
</p>
</div>
<div class="refsect1" id="description">
<h2>Description</h2>
<p>
<code class="varname">gl_PrimitiveID</code> is a tessellation control, tessellation evaluation
and fragment language input variable. For the tessellation control and tessellation
evaluation languages, it holds the number of primitives processed by
the shader since the current set of rendering primitives was started. The first
primitive processed by the drawing command is numbered zero and the primitive ID counter is incremented after every individual point, line
or triangle primitive is processed. For triangles drawn in point or line mode, the
primitive ID counter is incremented only once, even through multiple points or lines
may actually be drawn. Restarting a primitive topology using the primitive restart
index has no effect on the primitive ID counter.
</p>
<p>
In the geometry language, <code class="varname">gl_PrimitiveID</code> is an output
variable that is passed to the corresponding <code class="varname">gl_PrimitiveID</code> input
variable in the fragment shader. If no geomery shader is present then <code class="varname">gl_PrimitiveID</code>
in the fragment language behaves identically as it would in the tessellation control and evaluation
languages. If a geometry shader is present but does not write to <code class="varname">gl_PrimitiveID</code>,
the value of <code class="varname">gl_PrimitiveID</code> in the fragment shader is undefined.
</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>
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<th style="text-align: left; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>Function 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>1.30</strong></span>
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<span class="bold"><strong>1.40</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>
</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 ; border-bottom: 2px solid ; "><code class="varname">gl_PrimitiveID</code> (Fragment and Geometry Languages)</td>
<td style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">-</td>
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<td style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">✔</td>
<td style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">✔</td>
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<td style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">✔</td>
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<td style="text-align: center; border-bottom: 2px solid ; ">✔</td>
</tr>
<tr>
<td style="text-align: left; border-right: 2px solid ; "><code class="varname">gl_PrimitiveID</code> (Tessellation Control and Evaluation Languages)</td>
<td style="text-align: center; border-right: 2px solid ; ">-</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="seealso">
<h2>See Also</h2>
<p>
<a class="citerefentry" href="gl_InstanceID.xhtml"><span class="citerefentry"><span class="refentrytitle">gl_InstanceID</span></span></a>,
<a class="citerefentry" href="gl_VertexID.xhtml"><span class="citerefentry"><span class="refentrytitle">gl_VertexID</span></span></a>,
<a class="citerefentry" href="gl_PrimitiveIDIn.xhtml"><span class="citerefentry"><span class="refentrytitle">gl_PrimitiveIDIn</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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