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<!DOCTYPE html><html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>gl_Position - OpenGL 4 Reference Pages</title>
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<div class="refentry" id="gl_Position">
<div class="titlepage"/>
<div class="refnamediv">
<h2>Name</h2>
<p>gl_Position — contains the position of the current vertex</p>
</div>
<div class="refsynopsisdiv">
<h2>Declaration</h2>
<p>
<code class="varname">gl_Position</code> is a member of the
<code class="varname">gl_PerVertex</code> named block:
</p>
<pre class="programlisting"> out gl_PerVertex {
vec4 gl_Position;
float gl_PointSize;
float gl_ClipDistance[];
};</pre>
<p>
</p>
</div>
<div class="refsect1" id="description">
<h2>Description</h2>
<p>
In the vertex, tessellation evaluation and geometry languages, a single
global instance of the <code class="varname">gl_PerVertex</code> named block is available and
its <code class="varname">gl_Position</code> member is an output that receives the
homogeneous vertex position. It may be written at any time during shader execution.
The value written to <code class="varname">gl_Position</code> will be used by primitive assembly,
clipping, culling and other fixed functionality operations, if present, that operate on
primitives after vertex processing has occurred.
</p>
<p>
In the tessellation control language, the <code class="varname">gl_PerVertex</code> named block
is used to construct an array, <code class="varname">gl_out[]</code>, whose <code class="varname">gl_Position</code>
members hold the homogeneous control point position, which become available as inputs to the subsequent
tessellation evaluation shader.
</p>
<p>
The value of <code class="varname">gl_Position</code> (or the <code class="varname">gl_Position</code> member of the <code class="varname">gl_out[]</code>
array, in the case of the tessellation control shader)
is undefined after the vertex, tessellation control, and tessellation evaluation
shading stages if the corresponding shader executable does
not write to gl_Position. It is also undefined after the geometry processing stage if the geometry shader executable calls
<a class="citerefentry" href="EmitVertex.xhtml"><span class="citerefentry"><span class="refentrytitle">EmitVertex</span></span></a> without having
written <code class="varname">gl_Position</code> since the last call to <a class="citerefentry" href="EmitVertex.xhtml"><span class="citerefentry"><span class="refentrytitle">EmitVertex</span></span></a>
(or hasn't written it at all).
</p>
<p>
In the tessellation control, tessellation evaluation and geometry languages,
the <code class="varname">gl_PerVertex</code> named block is used to construct an array, <code class="varname">gl_in[]</code>
of per-vertex or per-control point inputs whose content represents the corresponding
outputs written by the previous stage.
</p>
</div>
<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 ; ">
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<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>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>
</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_Position</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>
<p>Versions 1.10 to 1.40 - vertex shader only.</p>
<p>Versions 1.50 to 3.30 - vertex and geometry shaders only.</p>
</div>
<div class="refsect1" id="seealso">
<h2>See Also</h2>
<p>
<a class="citerefentry" href="gl_PointSize.xhtml"><span class="citerefentry"><span class="refentrytitle">gl_PointSize</span></span></a>, <a class="citerefentry" href="gl_ClipDistance.xhtml"><span class="citerefentry"><span class="refentrytitle">gl_ClipDistance</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>
</div>
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