| 1 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd"> |
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| 3 | <?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" /><title>glFrontFace</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></head><body><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 border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><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> |
| 4 | Specifies the orientation of front-facing polygons. |
| 5 | <code class="constant">GL_CW</code> and <code class="constant">GL_CCW</code> are accepted. |
| 6 | The initial value is <code class="constant">GL_CCW</code>. |
| 7 | </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p> |
| 8 | In a scene composed entirely of opaque closed surfaces, |
| 9 | back-facing polygons are never visible. |
| 10 | Eliminating these invisible polygons has the obvious benefit |
| 11 | of speeding up the rendering of the image. |
| 12 | 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> |
| 13 | 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>. |
| 14 | </p><p> |
| 15 | The projection of a polygon to window coordinates is said to have |
| 16 | clockwise winding if an imaginary object following the path |
| 17 | from its first vertex, |
| 18 | its second vertex, |
| 19 | and so on, |
| 20 | to its last vertex, |
| 21 | and finally back to its first vertex, |
| 22 | moves in a clockwise direction about the interior of the polygon. |
| 23 | The polygon's winding is said to be counterclockwise if the imaginary |
| 24 | object following the same path moves in a counterclockwise direction |
| 25 | about the interior of the polygon. |
| 26 | <code class="function">glFrontFace</code> specifies whether polygons with clockwise winding in window coordinates, |
| 27 | or counterclockwise winding in window coordinates, |
| 28 | are taken to be front-facing. |
| 29 | Passing <code class="constant">GL_CCW</code> to <em class="parameter"><code>mode</code></em> selects counterclockwise polygons as |
| 30 | front-facing; |
| 31 | <code class="constant">GL_CW</code> selects clockwise polygons as front-facing. |
| 32 | By default, counterclockwise polygons are taken to be front-facing. |
| 33 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p> |
| 34 | <code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>mode</code></em> is not an accepted value. |
| 35 | </p><p> |
| 36 | <code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glFrontFace</code> |
| 37 | is executed between the execution of <a class="citerefentry" href="glBegin.xml"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a> |
| 38 | and the corresponding execution of <a class="citerefentry" href="glEnd.xml"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>. |
| 39 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p> |
| 40 | <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> |
| 41 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p> |
| 42 | <a class="citerefentry" href="glCullFace.xml"><span class="citerefentry"><span class="refentrytitle">glCullFace</span></span></a>, |
| 43 | <a class="citerefentry" href="glLightModel.xml"><span class="citerefentry"><span class="refentrytitle">glLightModel</span></span></a> |
| 44 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p> |
| 45 | Copyright <span class="trademark"></span>© 1991-2006 |
| 46 | Silicon Graphics, Inc. This document is licensed under the SGI |
| 47 | Free Software B License. For details, see |
| 48 | <a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>. |
| 49 | </p></div></div></body></html> |