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<!DOCTYPE refentry [ <!ENTITY % mathent SYSTEM "math.ent"> %mathent; ]>
<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="gl_CullDistance">
<info>
<copyright>
<year>2014</year>
<holder>Khronos Group</holder>
</copyright>
</info>
<refmeta>
<refentrytitle>gl_CullDistance</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>gl_CullDistance</refname>
<refpurpose>provides a mechanism for controlling user culling</refpurpose>
</refnamediv>
<refsynopsisdiv>
<title>Declaration</title>
<para>
<varname>gl_CullDistance</varname> is a member of the
<varname>gl_PerVertex</varname> named block:
<programlisting> out gl_PerVertex {
vec4 gl_Position;
float gl_PointSize;
float gl_ClipDistance[];
float gl_CullDistance[];
};</programlisting>
</para>
<para>
In fragment shaders, it is intrinsically declared as:
<fieldsynopsis>
<modifier>in</modifier>
<type>float</type>
<varname>gl_CullDistance[]</varname>
</fieldsynopsis>
</para>
</refsynopsisdiv>
<refsect1 xml:id="description"><title>Description</title>
<para>
The <varname>gl_CullDistance</varname> variable provides a
mechanism for controlling user culling. The element
<parameter>gl_CullDistance</parameter>[<emphasis>i</emphasis>]
specifies a cull distance for each plane <emphasis>i</emphasis>.
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 <emphasis>i</emphasis> will be
discarded.
</para>
<para>
The <varname>gl_CullDistance</varname> 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
<varname>gl_MaxCullDistances</varname>. The number of varying
components consumed by <varname>gl_CullDistance</varname> will
match the size of the array. Shaders writing
<varname>gl_CullDistance</varname> must write all enabled
distances, or culling results are undefined.
</para>
<para>
As an output variable,
<varname>gl_CullDistance</varname> 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
<varname>gl_CullDistance</varname> array contains linearly
interpolated values for the vertex values written by a shader to
the <varname>gl_CullDistance</varname> vertex output variable.
</para>
<para>
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
<varname>gl_ClipDistance</varname> and
<varname>gl_CullDistance</varname> arrays to be larger than
<varname>gl_MaxCombinedClipAndCullDistances</varname>.
</para>
</refsect1>
<refsect1 xml:id="versions"><title>Version Support</title>
<informaltable>
<tgroup cols="13" align="left">
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="varhead.xml" xpointer="xpointer(/*/*)"/>
<tbody>
<row>
<entry>gl_CullDistance</entry>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="version.xml" xpointer="xpointer(/*/*[@role='45']/*)"/>
</row>
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 xml:id="seealso"><title>See Also</title>
<para>
<citerefentry><refentrytitle>gl_ClipDistance</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>gl_PointSize</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 xml:id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="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.
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://opencontent.org/openpub/">http://opencontent.org/openpub/</link>.
</para>
</refsect1>
</refentry>
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