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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>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> |