upstream-doc/manglsl/xhtml/gl_FrontFacing.xml

   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>gl_FrontFacing - OpenGL Shading Language (GLSL)</title><meta name="generator" content="DocBook XSL Stylesheets V1.69.1" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="gl_FrontFacing"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>gl_FrontFacing — indicates whether a primitive is front or back facing</p></div><div class="refsynopsisdiv"><h2>Declaration</h2><div class="funcsynopsis"><code class="function">in bool gl_FrontFacing;</code></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
   5             Available only in the fragment language, <code class="function">gl_FrontFacing</code> is an input variable
   6             whose value is <code class="function">true</code> if the fragment belongs to a front-facing primitive and
   7             false otherwise. The determination of whether a triangle primitive is front-facing is made by
   8             examining the sign of the area of the triangle, including a possible reversal of this sign
   9             as controlled by <code class="function">glFrontFace</code>. One way to compute this area is:
  10         </p><p>
  11             <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
  12                 <mml:mi>a</mml:mi><mml:mo>=</mml:mo><mml:mfrac><mml:mrow><mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:mfrac>
  13                 <mml:msubsup><mml:mo>∑</mml:mo><mml:mrow>
  14                     <mml:mi>j</mml:mi><mml:mo>=</mml:mo><mml:mn>0</mml:mn>
  15                 </mml:mrow>
  16                 <mml:mrow>
  17                     <mml:mi>n</mml:mi><mml:mo>-</mml:mo><mml:mn>1</mml:mn>
  18                 </mml:mrow></mml:msubsup>
  19                 <mml:msubsup><mml:mi>x</mml:mi><mml:mrow>w</mml:mrow><mml:mrow><mml:mi>i</mml:mi></mml:mrow></mml:msubsup>
  20                 <mml:msubsup><mml:mi>y</mml:mi><mml:mrow>w</mml:mrow><mml:mrow><mml:mi>i</mml:mi><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msubsup>
  21                 <mml:mo>-</mml:mo>
  22                 <mml:msubsup><mml:mi>x</mml:mi><mml:mrow>w</mml:mrow><mml:mrow><mml:mi>i</mml:mi><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msubsup>
  23                 <mml:msubsup><mml:mi>y</mml:mi><mml:mrow>w</mml:mrow><mml:mrow><mml:mi>i</mml:mi></mml:mrow></mml:msubsup>
  24             </mml:math>
  25         </p><p>
  26             where <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:msubsup><mml:mi>x</mml:mi><mml:mrow>w</mml:mrow><mml:mrow><mml:mi>i</mml:mi></mml:mrow></mml:msubsup></mml:math> and
  27             <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:msubsup><mml:mi>y</mml:mi><mml:mrow>w</mml:mrow><mml:mrow><mml:mi>i</mml:mi></mml:mrow></mml:msubsup></mml:math> are
  28             the x and y window coordinates of the <span class="emphasis"><em>i</em></span>th vertex of the n-vertex polygon.
  29         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="versions"></a><h2>Version Support</h2><div class="informaltable"><table border="1"><colgroup><col align="left" /><col align="center" /><col align="center" /></colgroup><thead><tr><th align="left"><span class="bold"><strong>
  30                         Variable
  31                         </strong></span></th><th align="left"><span class="bold"><strong>
  32                         Version 1.10
  33                         </strong></span></th><th align="left"><span class="bold"><strong>
  34                         Version 1.20
  35                         </strong></span></th><th align="left"><span class="bold"><strong>
  36                         Version 1.30
  37                         </strong></span></th><th align="left"><span class="bold"><strong>
  38                         Version 1.40
  39                         </strong></span></th><th align="left"><span class="bold"><strong>
  40                         Version 1.50
  41                         </strong></span></th><th align="left"><span class="bold"><strong>
  42                         Version 3.30
  43                         </strong></span></th><th align="left"><span class="bold"><strong>
  44                         Version 4.00
  45                         </strong></span></th><th align="left"><span class="bold"><strong>
  46                         Version 4.10
  47                         </strong></span></th></tr><tr><th align="left">
  48                             gl_FrontFacing
  49                         </th><th align="center">
  50                             <span class="emphasis"><em>Y</em></span>
  51                         </th><th align="center">
  52                             <span class="emphasis"><em>Y</em></span>
  53                         </th><th align="center">
  54                             <span class="emphasis"><em>Y</em></span>
  55                         </th><th align="center">
  56                             <span class="emphasis"><em>Y</em></span>
  57                         </th><th align="center">
  58                             <span class="emphasis"><em>Y</em></span>
  59                         </th><th align="center">
  60                             <span class="emphasis"><em>Y</em></span>
  61                         </th><th align="center">
  62                             <span class="emphasis"><em>Y</em></span>
  63                         </th><th align="center">
  64                             <span class="emphasis"><em>Y</em></span>
  65                         </th></tr></thead></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
  66             <a href="gl_FragCoord.xml"><span class="citerefentry"><span class="refentrytitle">gl_FragCoord</span></span></a>
  67         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
  68             Copyright <span class="trademark"></span>© 2011 Khronos Group.
  69             This material may be distributed subject to the terms and conditions set forth in
  70             the Open Publication License, v 1.0, 8 June 1999.
  71             <a href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
  72         </p></div></div></body></html>