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<title>gl_CullDistance - OpenGL 4 Reference Pages</title>
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<div class="refentry" id="gl_CullDistance">
<div class="titlepage"/>
<div class="refnamediv">
<h2>Name</h2>
<p>gl_CullDistance — provides a mechanism for controlling user culling</p>
</div>
<div class="refsynopsisdiv">
<h2>Declaration</h2>
<p>
<code class="varname">gl_CullDistance</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[];
float gl_CullDistance[];
};</pre>
<p>
</p>
<p>
In fragment shaders, it is intrinsically declared as:
<code class="fieldsynopsis"><span class="modifier">in </span><span class="type">float </span><span class="varname">gl_CullDistance[] </span>;</code>
</p>
</div>
<div class="refsect1" id="description">
<h2>Description</h2>
<p>
The <code class="varname">gl_CullDistance</code> variable provides a
mechanism for controlling user culling. The element
<em class="parameter"><code>gl_CullDistance</code></em>[<span class="emphasis"><em>i</em></span>]
specifies a cull distance for each plane <span class="emphasis"><em>i</em></span>.
A distance of 0.0 means that the vertex is on the plane, a
positive distance means that the vertex is insider the cull
volume, and a negative distance means that the point is outside
the cull volume. Primitives whose vertices all have a negative
clip distance for plane <span class="emphasis"><em>i</em></span> will be
discarded.
</p>
<p>
The <code class="varname">gl_CullDistance</code> array is predeclared as
unsized and must be sized by the shader either by redeclaring it
with an size or by indexing it only with integral constant
expressions. The size determines the number and set of enabled
cull distances and can be at most
<code class="varname">gl_MaxCullDistances</code>. The number of varying
components consumed by <code class="varname">gl_CullDistance</code> will
match the size of the array. Shaders writing
<code class="varname">gl_CullDistance</code> must write all enabled
distances, or culling results are undefined.
</p>
<p>
As an output variable,
<code class="varname">gl_CullDistance</code> provides the place for the
shader to write these distances. As an input in all but the
fragment language, it reads the values written in the previous
shader stage. In the fragment language, the
<code class="varname">gl_CullDistance</code> array contains linearly
interpolated values for the vertex values written by a shader to
the <code class="varname">gl_CullDistance</code> vertex output variable.
</p>
<p>
It is a compile-time or link-time error for the set of shaders
forming a program to have the sum of the sizes of the
<code class="varname">gl_ClipDistance</code> and
<code class="varname">gl_CullDistance</code> arrays to be larger than
<code class="varname">gl_MaxCombinedClipAndCullDistances</code>.
</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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<span class="bold"><strong>Variable Name</strong></span>
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<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<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>1.40</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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<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
<span class="bold"><strong>4.40</strong></span>
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<th style="text-align: center; border-bottom: 2px solid ; ">
<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_CullDistance</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; ">✔</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="refsect1" id="seealso">
<h2>See Also</h2>
<p>
<a class="citerefentry" href="gl_ClipDistance.xhtml"><span class="citerefentry"><span class="refentrytitle">gl_ClipDistance</span></span></a>,
<a class="citerefentry" href="gl_PointSize.xhtml"><span class="citerefentry"><span class="refentrytitle">gl_PointSize</span></span></a>
</p>
</div>
<div class="refsect1" id="Copyright">
<h2>Copyright</h2>
<p>
Copyright <span class="trademark"/>© 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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