<div class="refentry" id="atan">

<div class="titlepage"></div>

<div class="refnamediv">

<h2>Name</h2>

<p>atan — return the arc-tangent of the parameters</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">atan</strong>(</code>

</td>

<td>genType <var class="pdparam">y</var>, </td>

</tr>

<tr>

<td> </td>

<td>genType <var class="pdparam">x</var><code>)</code>;</td>

</tr>

</table>

<div class="funcprototype-spacer"> </div>

</div>

<div class="funcsynopsis">

<table style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">

<tr>

<td>

<code class="funcdef">genType <strong class="fsfunc">atan</strong>(</code>

</td>

<td>genType <var class="pdparam">y_over_x</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>y</code>

</em>

</span>

</dt>

<dd>

<p>

Specify the numerator of the fraction whose arctangent to return.

</p>

</dd>

<dt>

<span class="term">

<em class="parameter">

<code>x</code>

</em>

</span>

</dt>

<dd>

<p>

Specify the denominator of the fraction whose arctangent to return.

</p>

</dd>

<dt>

<span class="term">

<em class="parameter">

<code>y_over_x</code>

</em>

</span>

</dt>

<dd>

<p>

Specify the fraction whose arctangent to return.

</p>

</dd>

</dl>

</div>

</div>

<div class="refsect1" id="description">

<h2>Description</h2>

<p>

<code class="function">atan</code> returns the angle whose trigonometric arctangent is

<math overflow="scroll">

<mfrac>

<mrow>

<mi mathvariant="italic">y</mi>

</mrow>

<mrow>

<mi mathvariant="italic">x</mi>

</mrow>

</mfrac>

</math> or <math overflow="scroll"><mi mathvariant="italic">y_over_x</mi></math>,

depending on which overload is invoked. In the first overload, the signs of <math overflow="scroll"><mi mathvariant="italic">y</mi></math>

and <math overflow="scroll"><mi mathvariant="italic">x</mi></math> are used to determine the quadrant

that the angle lies in. The values returned by <code class="function">atan</code> in this case are in the range

<math overflow="scroll">

<mfenced open="[" close="]">

<mrow>

<mo>−</mo>

<mi>π</mi>

</mrow>

<mi>π</mi>

</mfenced>

</math>. Results are undefined if <math overflow="scroll"><mi mathvariant="italic">x</mi></math> is zero.

</p>

<p>

For the second overload, <code class="function">atan</code> returns the angle whose tangent is

<math overflow="scroll"><mi mathvariant="italic">y_over_x</mi></math>. Values

returned in this case are in the range

<math overflow="scroll">

<mfenced open="[" close="]">

<mrow>

<mo>−</mo>

<mfrac>

<mi>π</mi>

<mn>2</mn>

</mfrac>

</mrow>

<mfrac>

<mi>π</mi>

<mn>2</mn>

</mfrac>

</mfenced>

</math>.

</p>

</div>

{$pipelinestall}{$examples}

<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 ; ">

<colgroup>

<col style="text-align: left; "/>

<col style="text-align: center; " class="firstvers"/>

<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; "/>

<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 ; ">atan</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="sin"><span class="citerefentry"><span class="refentrytitle">sin</span></span></a>,

<a class="citerefentry" href="cos"><span class="citerefentry"><span class="refentrytitle">cos</span></span></a>,

<a class="citerefentry" href="tan"><span class="citerefentry"><span class="refentrytitle">tan</span></span></a>

</p>

</div>

<div class="refsect1" id="Copyright">

<h2>Copyright</h2>

<p>

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.

<a class="link" href="https://opencontent.org/openpub/" target="_top">https://opencontent.org/openpub/</a>.

</p>

</div>

</div>