Return to glFrontFace.xml CVS log

Up to [Development] / projects / ogl-sample / main / doc / gles / xml

OpenGL ES 1.0 and EGL 1.0 reference manual and man pages (written by
Claude Knaus, based on OpenGL SI man pages).

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook V4.2//EN" "DTD/docbook/docbookx.dtd">

<!--
  License Applicability. Except to the extent portions of this file are
  made subject to an alternative license as permitted in the SGI Free
  Software License B, Version 1.1 (the "License"), the contents of this
  file are subject only to the provisions of the License. You may not use
  this file except in compliance with the License. You may obtain a copy
  of the License at Silicon Graphics, Inc., attn: Legal Services, 1600
  Amphitheatre Parkway, Mountain View, CA 94043-1351, or at:

  http://oss.sgi.com/projects/FreeB

  Note that, as provided in the License, the Software is distributed on an
  "AS IS" basis, with ALL EXPRESS AND IMPLIED WARRANTIES AND CONDITIONS
  DISCLAIMED, INCLUDING, WITHOUT LIMITATION, ANY IMPLIED WARRANTIES AND
  CONDITIONS OF MERCHANTABILITY, SATISFACTORY QUALITY, FITNESS FOR A
  PARTICULAR PURPOSE, AND NON-INFRINGEMENT.

  Original Code. The Original Code is: OpenGL ES Reference Manual,
  Version 1.0, released September 2003, developed by Silicon Graphics,
  Inc.  The Original Code is Copyright (c) 2003 Silicon Graphics, Inc.
  Copyright in any portions created by third parties is as indicated
  elsewhere herein.  All Rights Reserved.
-->

<refentry id="glFrontFace">
  <refmeta>
    <refentrytitle>glFrontFace</refentrytitle>
    <manvolnum>3G</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>glFrontFace</refname>
    <refpurpose>define front- and back-facing polygons</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <title>C Specification</title>

    <funcsynopsis>
      <funcprototype>
        <funcdef>void <function>glFrontFace</function></funcdef>
        <paramdef>GLenum <parameter>mode</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Parameters</title>

    <variablelist>
      <varlistentry>
        <term>
          <parameter>mode</parameter>
        </term>

        <listitem>
          <para>Specifies the orientation of front-facing polygons.
          <constant>GL_CW</constant> and 
          <constant>GL_CCW</constant> are accepted. The initial value is 
          <constant>GL_CCW</constant>.</para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>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 
    <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and 
    <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry>
    with argument <constant>GL_CULL_FACE</constant>.
    Culling is initially disabled.
    </para>

    <para>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. 
    <function>glFrontFace</function>
    specifies whether polygons with clockwise winding in window
    coordinates, or counterclockwise winding in window coordinates,
    are taken to be front-facing. Passing 
    <constant>GL_CCW</constant> to <parameter>mode</parameter>
    selects counterclockwise polygons as front-facing. 
    <constant>GL_CW</constant>
    selects clockwise polygons as front-facing. By default,
    counterclockwise polygons are taken to be front-facing.</para>
  </refsect1>

  <refsect1>
    <title>Errors</title>

    <para><constant>GL_INVALID_ENUM</constant> is generated if 
    <parameter>mode</parameter> is not an accepted value.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>

    <para>
    <citerefentry><refentrytitle>glCullFace</refentrytitle></citerefentry>, 
    <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>, 
    <citerefentry><refentrytitle>glLightModel</refentrytitle></citerefentry>
    </para>
  </refsect1>
</refentry>