<div class="refentry" lang="en" xml:lang="en"><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"><h2>C Specification</h2><div class="funcsynopsis"><table><tr><td><code class="funcdef">void <b class="fsfunc">glFrontFace</b>(</code></td><td>GLenum  </td><td><var class="pdparam">mode</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><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" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>

In a scene composed entirely of opaque closed surfaces,

back-facing polygons are never visible.

Eliminating these invisible polygons has the obvious benefit

of speeding up the rendering of the image.

To enable and disable elimination of back-facing polygons, 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>.

</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" lang="en" xml:lang="en"><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><p>

<code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glFrontFace</code>

is executed between the execution of <a class="citerefentry" href="glBegin"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a>

and the corresponding execution of <a class="citerefentry" href="glEnd"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.

</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p>

<a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_FRONT_FACE</code>

</p></div>

{$pipelinestall}{$examples}

<div class="refsect1" lang="en" xml:lang="en"><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="glLightModel"><span class="citerefentry"><span class="refentrytitle">glLightModel</span></span></a>

</p></div><div class="refsect1" lang="en" xml:lang="en"><div id="Copyright"><h2>Copyright</h2><p>

Copyright © 1991-2006

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></div>