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1 | <?xml version="1.0" encoding="UTF-8"?> |
2 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd"> | |
3 | <!-- saved from url=(0013)about:internet --> | |
4 | <?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" pref:renderer="mathplayer-dl"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><link rel="stylesheet" type="text/css" href="opengl-man.css" /><title>glFrontFace</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /></head><body><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 border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" 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> | |
5 | Specifies the orientation of front-facing polygons. | |
6 | <code class="constant">GL_CW</code> and <code class="constant">GL_CCW</code> are accepted. | |
7 | The initial value is <code class="constant">GL_CCW</code>. | |
8 | </p></dd></dl></div></div><div class="refsect1" title="Description"><a id="description"></a><h2>Description</h2><p> | |
9 | In a scene composed entirely of opaque closed surfaces, | |
10 | back-facing polygons are never visible. | |
11 | Eliminating these invisible polygons has the obvious benefit | |
12 | of speeding up the rendering of the image. | |
13 | To enable and disable elimination of back-facing polygons, call <a class="citerefentry" href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a> | |
14 | and <a class="citerefentry" href="glDisable.xml"><span class="citerefentry"><span class="refentrytitle">glDisable</span></span></a> with argument <code class="constant">GL_CULL_FACE</code>. | |
15 | </p><p> | |
16 | The projection of a polygon to window coordinates is said to have | |
17 | clockwise winding if an imaginary object following the path | |
18 | from its first vertex, | |
19 | its second vertex, | |
20 | and so on, | |
21 | to its last vertex, | |
22 | and finally back to its first vertex, | |
23 | moves in a clockwise direction about the interior of the polygon. | |
24 | The polygon's winding is said to be counterclockwise if the imaginary | |
25 | object following the same path moves in a counterclockwise direction | |
26 | about the interior of the polygon. | |
27 | <code class="function">glFrontFace</code> specifies whether polygons with clockwise winding in window coordinates, | |
28 | or counterclockwise winding in window coordinates, | |
29 | are taken to be front-facing. | |
30 | Passing <code class="constant">GL_CCW</code> to <em class="parameter"><code>mode</code></em> selects counterclockwise polygons as | |
31 | front-facing; | |
32 | <code class="constant">GL_CW</code> selects clockwise polygons as front-facing. | |
33 | By default, counterclockwise polygons are taken to be front-facing. | |
34 | </p></div><div class="refsect1" title="Errors"><a id="errors"></a><h2>Errors</h2><p> | |
35 | <code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>mode</code></em> is not an accepted value. | |
36 | </p></div><div class="refsect1" title="Associated Gets"><a id="associatedgets"></a><h2>Associated Gets</h2><p> | |
37 | <a class="citerefentry" href="glGet.xml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_FRONT_FACE</code> | |
38 | </p></div><div class="refsect1" title="See Also"><a id="seealso"></a><h2>See Also</h2><p> | |
39 | <a class="citerefentry" href="glCullFace.xml"><span class="citerefentry"><span class="refentrytitle">glCullFace</span></span></a>, | |
40 | </p></div><div class="refsect1" title="Copyright"><a id="Copyright"></a><h2>Copyright</h2><p> | |
41 | Copyright <span class="trademark"></span>© 1991-2006 | |
42 | Silicon Graphics, Inc. This document is licensed under the SGI | |
43 | Free Software B License. For details, see | |
44 | <a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>. | |
45 | </p></div></div></body></html> |