<div class="refentry" title="glFrontFace"><a id="glFrontFace"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glFrontFace — define front- and back-facing polygons</p></div><div class="refsynopsisdiv" title="C Specification"><h2>C Specification</h2><div class="funcsynopsis"><table class="funcprototype-table"><tr><td><code class="funcdef">void <b class="fsfunc">glFrontFace</b>(</code></td><td>GLenum <var class="pdparam">mode</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1" title="Parameters"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term">

<em class="parameter"><code>mode</code></em>

</span></dt><dd><p>Specifies the orientation of front-facing polygons.

<code class="constant">GL_CW</code> and

<code class="constant">GL_CCW</code> are accepted. The initial value is

<code class="constant">GL_CCW</code>.</p></dd></dl></div></div><div class="refsect1" title="Description"><a id="description"></a><h2>Description</h2><p>In a scene composed entirely of opaque closed surfaces,

back-facing polygons are never visible. Eliminating (culling) these

invisible polygons has the obvious benefit of speeding up the

rendering of the image. To enable and disable culling, call

<a class="citerefentry" href="glEnable"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a> and

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

with argument <code class="constant">GL_CULL_FACE</code>.

Culling is initially disabled.

</p><p>The projection of a polygon to window coordinates is said

to have clockwise winding if an imaginary object following the

path from its first vertex, its second vertex, and so on, to

its last vertex, and finally back to its first vertex, moves in

a clockwise direction about the interior of the polygon. The

polygon's winding is said to be counterclockwise if the

imaginary object following the same path moves in a

counterclockwise direction about the interior of the polygon.

<code class="function">glFrontFace</code>

specifies whether polygons with clockwise winding in window

coordinates, or counterclockwise winding in window coordinates,

are taken to be front-facing. Passing

<code class="constant">GL_CCW</code> to <em class="parameter"><code>mode</code></em>

selects counterclockwise polygons as front-facing.

<code class="constant">GL_CW</code>

selects clockwise polygons as front-facing. By default,

counterclockwise polygons are taken to be front-facing.</p></div><div class="refsect1" title="Errors"><a id="errors"></a><h2>Errors</h2><p><code class="constant">GL_INVALID_ENUM</code> is generated if

<em class="parameter"><code>mode</code></em> is not an accepted value.</p></div><div class="refsect1" title="See Also"><a id="seealso"></a><h2>See Also</h2><p>

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

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

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

</p></div><div class="refsect1" title="Copyright"><a id="copyright"></a><h2>Copyright</h2><p>

Copyright © 2003-2004

Silicon Graphics, Inc. This document is licensed under the SGI

Free Software B License. For details, see

<a class="ulink" href="https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/" target="_top">https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/</a>.

</p></div></div>