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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html><html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>dFdx, dFdy - OpenGL 4 Reference Pages</title>
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<header/>
<div class="refentry" id="dFdx">
<div class="titlepage"/>
<div class="refnamediv">
<h2>Name</h2>
<p>dFdx, dFdy — return the partial derivative of an argument with respect to x or y</p>
</div>
<div class="refsynopsisdiv">
<h2>Declaration</h2>
<div class="funcsynopsis">
<table style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">
<tr>
<td>
<code class="funcdef">genType <strong class="fsfunc">dFdx</strong>(</code>
</td>
<td>genType <var class="pdparam">p</var><code>)</code>;</td>
</tr>
</table>
<div class="funcprototype-spacer"> </div>
<table style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">
<tr>
<td>
<code class="funcdef">genType <strong class="fsfunc">dFdy</strong>(</code>
</td>
<td>genType <var class="pdparam">p</var><code>)</code>;</td>
</tr>
</table>
<div class="funcprototype-spacer"> </div>
<table style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">
<tr>
<td>
<code class="funcdef">genType <strong class="fsfunc">dFdxCoarse</strong>(</code>
</td>
<td>genType <var class="pdparam">p</var><code>)</code>;</td>
</tr>
</table>
<div class="funcprototype-spacer"> </div>
<table style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">
<tr>
<td>
<code class="funcdef">genType <strong class="fsfunc">dFdyCoarse</strong>(</code>
</td>
<td>genType <var class="pdparam">p</var><code>)</code>;</td>
</tr>
</table>
<div class="funcprototype-spacer"> </div>
<table style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">
<tr>
<td>
<code class="funcdef">genType <strong class="fsfunc">dFdxFine</strong>(</code>
</td>
<td>genType <var class="pdparam">p</var><code>)</code>;</td>
</tr>
</table>
<div class="funcprototype-spacer"> </div>
<table style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">
<tr>
<td>
<code class="funcdef">genType <strong class="fsfunc">dFdyFine</strong>(</code>
</td>
<td>genType <var class="pdparam">p</var><code>)</code>;</td>
</tr>
</table>
<div class="funcprototype-spacer"> </div>
</div>
</div>
<div class="refsect1" id="parameters">
<h2>Parameters</h2>
<div class="variablelist">
<dl class="variablelist">
<dt>
<span class="term">
<em class="parameter">
<code>p</code>
</em>
</span>
</dt>
<dd>
<p>
Specifies the expression of which to take the partial
derivative.
</p>
</dd>
</dl>
</div>
</div>
<div class="refsect1" id="description">
<h2>Description</h2>
<p>
<span class="emphasis"><em>Available only in the fragment shader</em></span>,
these functions return the partial derivative of expression
<em class="parameter"><code>p</code></em> with respect to the window $x$
coordinate (for <code class="function">dFdx*</code>) and $y$ coordinate
(for <code class="function">dFdy*</code>).
</p>
<p>
<code class="function">dFdxFine</code> and <code class="function">dFdyFine</code>
calculate derivatives using local differencing based on on the
value of <em class="parameter"><code>p</code></em> for the current fragment and
its immediate neighbor(s).
</p>
<p>
<code class="function">dFdxCoarse</code> and
<code class="function">dFdyCoarse</code> calculate derivatives using
local differencing based on the value of
<em class="parameter"><code>p</code></em> for the current fragment's neighbors,
and will possibly, but not necessarily, include the value for
the current fragment. That is, over a given area, the
implementation can compute derivatives in fewer unique locations
than would be allowed for the corresponding
<code class="function">dFdxFine</code> and <code class="function">dFdyFine</code>
functions.
</p>
<p>
<code class="function">dFdx</code> returns either
<code class="function">dFdxCoarse</code> or
<code class="function">dFdxFine</code>. <code class="function">dFdy</code> returns
either <code class="function">dFdyCoarse</code> or
<code class="function">dFdyFine</code>. The implementation may choose
which calculation to perform based upon factors such as
performance or the value of the API
<code class="constant">GL_FRAGMENT_SHADER_DERIVATIVE_HINT</code> hint.
</p>
<p>
Expressions that imply higher order
derivatives such as <code class="code">dFdx(dFdx(n))</code> have undefined
results, as do mixed-order derivatives such as
<code class="code">dFdx(dFdy(n))</code>. It is assumed that the expression
<em class="parameter"><code>p</code></em> is continuous and therefore,
expressions evaluated via non-uniform control flow may be
undefined.
</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; " 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 ; border-bottom: 2px solid ; ">dFdx</td>
<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>
<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>
<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>
<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>
<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>
<td style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">✔</td>
<td style="text-align: center; border-bottom: 2px solid ; ">✔</td>
</tr>
<tr>
<td style="text-align: left; border-right: 2px solid ; border-bottom: 2px solid ; ">dFdy</td>
<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>
<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>
<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>
<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>
<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>
<td style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">✔</td>
<td style="text-align: center; border-bottom: 2px solid ; ">✔</td>
</tr>
<tr>
<td style="text-align: left; border-right: 2px solid ; ">dFdxCoarse, dFdxFine, dFdyCoarse, dFdyFine</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>
</div>
<div class="refsect1" id="seealso">
<h2>See Also</h2>
<p>
<a class="citerefentry" href="fwidth.xhtml"><span class="citerefentry"><span class="refentrytitle">fwidth</span></span></a>,
<a class="citerefentry" href="glHint.xhtml"><span class="citerefentry"><span class="refentrytitle">glHint</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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