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<!DOCTYPE refentry [ <!ENTITY % mathent SYSTEM "math.ent"> %mathent; ]>
<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="fwidth">
<info>
<copyright>
<year>2011-2014</year>
<holder>Khronos Group</holder>
</copyright>
</info>
<refmeta>
<refentrytitle>fwidth</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>fwidth</refname>
<refpurpose>return the sum of the absolute value of derivatives in x and y</refpurpose>
</refnamediv>
<refsynopsisdiv><title>Declaration</title>
<funcsynopsis>
<funcprototype>
<funcdef>genType <function>fwidth</function></funcdef>
<paramdef>genType <parameter>p</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>genType <function>fwidthCoarse</function></funcdef>
<paramdef>genType <parameter>p</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>genType <function>fwidthFine</function></funcdef>
<paramdef>genType <parameter>p</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 xml:id="parameters"><title>Parameters</title>
<variablelist>
<varlistentry>
<term><parameter>p</parameter></term>
<listitem>
<para>
Specifies the expression of which to take the partial
derivative.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 xml:id="description"><title>Description</title>
<para>
<emphasis>Available only in the fragment shader</emphasis>,
these functions return the sum of the absolute derivatives in
$x$ and $y$ using local differencing for the input argument
<parameter>p</parameter>.
<function>fwidth</function> is equivalent to
<code>
<function>abs</function>(<parameter>dFdx</parameter>(p)) +
<function>abs</function>(<parameter>dFdy</parameter>(p))
</code>.
<function>fwidthCoarse</function> is equivalent to
<code>
<function>abs</function>(<parameter>dFdxCoarse</parameter>(p)) +
<function>abs</function>(<parameter>dFdyCoarse</parameter>(p))
</code>.
<function>fwidthFine</function> is equivalent to
<code>
<function>abs</function>(<parameter>dFdxFine</parameter>(p)) +
<function>abs</function>(<parameter>dFdyFine</parameter>(p))
</code>.
</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="funchead.xml" xpointer="xpointer(/*/*)"/>
<tbody>
<row>
<entry>fwidth</entry>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="version.xml" xpointer="xpointer(/*/*[@role='11']/*)"/>
</row>
<row>
<entry>fwidthCoarse, fwidthFine</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>dFdx</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 xml:id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"/> 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.
<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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