upstream-man-pages/man4/glFrontFace.xml

   1 <?xml version="1.0" encoding="UTF-8"?>
   2 <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
   3               "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
   4 <refentry id="glFrontFace">
   5     <refmeta>
   6         <refmetainfo>
   7             <copyright>
   8                 <year>1991-2006</year>
   9                 <holder>Silicon Graphics, Inc.</holder>
  10             </copyright>
  11         </refmetainfo>
  12         <refentrytitle>glFrontFace</refentrytitle>
  13         <manvolnum>3G</manvolnum>
  14     </refmeta>
  15     <refnamediv>
  16         <refname>glFrontFace</refname>
  17         <refpurpose>define front- and back-facing polygons</refpurpose>
  18     </refnamediv>
  19     <refsynopsisdiv><title>C Specification</title>
  20         <funcsynopsis>
  21             <funcprototype>
  22                 <funcdef>void <function>glFrontFace</function></funcdef>
  23                 <paramdef>GLenum <parameter>mode</parameter></paramdef>
  24             </funcprototype>
  25         </funcsynopsis>
  26     </refsynopsisdiv>
  27     <!-- eqn: ignoring delim $$ -->
  28     <refsect1 id="parameters"><title>Parameters</title>
  29         <variablelist>
  30         <varlistentry>
  31             <term><parameter>mode</parameter></term>
  32             <listitem>
  33                 <para>
  34                     Specifies the orientation of front-facing polygons.
  35                     <constant>GL_CW</constant> and <constant>GL_CCW</constant> are accepted.
  36                     The initial value is <constant>GL_CCW</constant>.
  37                 </para>
  38             </listitem>
  39         </varlistentry>
  40         </variablelist>
  41     </refsect1>
  42     <refsect1 id="description"><title>Description</title>
  43         <para>
  44             In a scene composed entirely of opaque closed surfaces,
  45             back-facing polygons are never visible.
  46             Eliminating these invisible polygons has the obvious benefit
  47             of speeding up the rendering of the image.
  48             To enable and disable elimination of back-facing polygons, call <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>
  49             and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> with argument <constant>GL_CULL_FACE</constant>.
  50         </para>
  51         <para>
  52             The projection of a polygon to window coordinates is said to have
  53             clockwise winding if an imaginary object following the path
  54             from its first vertex,
  55             its second vertex,
  56             and so on,
  57             to its last vertex,
  58             and finally back to its first vertex,
  59             moves in a clockwise direction about the interior of the polygon.
  60             The polygon's winding is said to be counterclockwise if the imaginary
  61             object following the same path moves in a counterclockwise direction
  62             about the interior of the polygon.
  63             <function>glFrontFace</function> specifies whether polygons with clockwise winding in window coordinates,
  64             or counterclockwise winding in window coordinates,
  65             are taken to be front-facing.
  66             Passing <constant>GL_CCW</constant> to <parameter>mode</parameter> selects counterclockwise polygons as
  67             front-facing;
  68             <constant>GL_CW</constant> selects clockwise polygons as front-facing.
  69             By default, counterclockwise polygons are taken to be front-facing.
  70         </para>
  71     </refsect1>
  72     <refsect1 id="errors"><title>Errors</title>
  73         <para>
  74             <constant>GL_INVALID_ENUM</constant> is generated if <parameter>mode</parameter> is not an accepted value.
  75         </para>
  76     </refsect1>
  77     <refsect1 id="associatedgets"><title>Associated Gets</title>
  78         <para>
  79             <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_FRONT_FACE</constant>
  80         </para>
  81     </refsect1>
  82     <refsect1 id="seealso"><title>See Also</title>
  83         <para>
  84             <citerefentry><refentrytitle>glCullFace</refentrytitle></citerefentry>,
  85         </para>
  86     </refsect1>
  87     <refsect1 id="Copyright"><title>Copyright</title>
  88         <para>
  89             Copyright <trademark class="copyright"></trademark> 1991-2006
  90             Silicon Graphics, Inc. This document is licensed under the SGI
  91             Free Software B License. For details, see
  92             <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
  93         </para>
  94     </refsect1>
  95 </refentry>