upstream-man-pages/man3/xhtml/glProvokingVertex.xml

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   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>glProvokingVertex</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /></head><body><div class="refentry" title="glProvokingVertex"><a id="glProvokingVertex"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glProvokingVertex — specifiy the vertex to be used as the source of data for flat shaded varyings</p></div><div class="refsynopsisdiv" title="C Specification"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">void <b class="fsfunc">glProvokingVertex</b>(</code></td><td>GLenum <var class="pdparam">provokeMode</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1" title="Parameters"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>provokeMode</code></em></span></dt><dd><p>
   5                     Specifies the vertex to be used as the source of data for flat shaded varyings.
   6                 </p></dd></dl></div></div><div class="refsect1" title="Description"><a id="description"></a><h2>Description</h2><p>
   7             <span class="emphasis"><em>Flatshading</em></span> a vertex shader varying output means to assign all vetices of the primitive the same value
   8             for that output. The vertex from which these values is derived is known as the <span class="emphasis"><em>provoking vertex</em></span> and
   9             <code class="function">glProvokingVertex</code> specifies which vertex is to be used as the source of data for flat shaded varyings.
  10         </p><p>
  11             <em class="parameter"><code>provokeMode</code></em> must be either <code class="constant">GL_FIRST_VERTEX_CONVENTION</code> or
  12             <code class="constant">GL_LAST_VERTEX_CONVENTION</code>, and controls the selection of the vertex whose values are assigned to flatshaded
  13             varying outputs. The interpretation of these values for the supported primitive types is:
  14             </p><div class="informaltable"><table border="1"><colgroup><col align="left" /><col align="left" /><col align="left" /></colgroup><thead><tr><th align="left"><span class="bold"><strong>
  15                             Primitive Type of Polygon <span class="emphasis"><em>i</em></span>
  16                             </strong></span></th><th align="left"><span class="bold"><strong>
  17                             First Vertex Convention
  18                             </strong></span></th><th align="left"><span class="bold"><strong>
  19                             Last Vertex Convention
  20                             </strong></span></th></tr><tr><th align="left">
  21                                 point
  22                             </th><th align="left">
  23                                 <span class="emphasis"><em>i</em></span>
  24                             </th><th align="left">
  25                                 <span class="emphasis"><em>i</em></span>
  26                             </th></tr><tr><th align="left">
  27                                 independent line
  28                             </th><th align="left">
  29                                 2<span class="emphasis"><em>i</em></span> - 1
  30                             </th><th align="left">
  31                                 2<span class="emphasis"><em>i</em></span>
  32                             </th></tr><tr><th align="left">
  33                                 line loop
  34                             </th><th align="left">
  35                                 <span class="emphasis"><em>i</em></span>
  36                             </th><th align="left">
  37                                 <p>
  38                                 <span class="emphasis"><em>i</em></span> + 1, if <span class="emphasis"><em>i</em></span> &lt; <span class="emphasis"><em>n</em></span>
  39                                 </p>
  40                                 <p>
  41                                 1, if <span class="emphasis"><em>i</em></span> = <span class="emphasis"><em>n</em></span>
  42                                 </p>
  43                             </th></tr><tr><th align="left">
  44                                 line strip
  45                             </th><th align="left">
  46                                 <span class="emphasis"><em>i</em></span>
  47                             </th><th align="left">
  48                                 <span class="emphasis"><em>i</em></span> + 1
  49                             </th></tr><tr><th align="left">
  50                                 independent triangle
  51                             </th><th align="left">
  52                                 3<span class="emphasis"><em>i</em></span> - 2
  53                             </th><th align="left">
  54                                 3<span class="emphasis"><em>i</em></span>
  55                             </th></tr><tr><th align="left">
  56                                 triangle strip
  57                             </th><th align="left">
  58                                 <span class="emphasis"><em>i</em></span>
  59                             </th><th align="left">
  60                                 <span class="emphasis"><em>i</em></span> + 2
  61                             </th></tr><tr><th align="left">
  62                                 triangle fan
  63                             </th><th align="left">
  64                                 <span class="emphasis"><em>i</em></span> + 1
  65                             </th><th align="left">
  66                                 <span class="emphasis"><em>i</em></span> + 2
  67                             </th></tr><tr><th align="left">
  68                                 line adjacency
  69                             </th><th align="left">
  70                                 4<span class="emphasis"><em>i</em></span> - 2
  71                             </th><th align="left">
  72                                 4<span class="emphasis"><em>i</em></span> - 1
  73                             </th></tr><tr><th align="left">
  74                                 line strip adjacency
  75                             </th><th align="left">
  76                                 <span class="emphasis"><em>i</em></span> + 1
  77                             </th><th align="left">
  78                                 <span class="emphasis"><em>i</em></span> + 2
  79                             </th></tr><tr><th align="left">
  80                                 triangle adjacency
  81                             </th><th align="left">
  82                                 6<span class="emphasis"><em>i</em></span> - 5
  83                             </th><th align="left">
  84                                 6<span class="emphasis"><em>i</em></span> - 1
  85                             </th></tr><tr><th align="left">
  86                                 triangle strip adjacency
  87                             </th><th align="left">
  88                                 2<span class="emphasis"><em>i</em></span> - 1
  89                             </th><th align="left">
  90                                 2<span class="emphasis"><em>i</em></span> + 3
  91                             </th></tr></thead></table></div><p>
  92         </p><p>
  93             If a vertex or geometry shader is active, user-defined varying outputs may be flatshaded by using the
  94             <code class="code">flat</code> qualifier when declaring the output.
  95         </p></div><div class="refsect1" title="Notes"><a id="notes"></a><h2>Notes</h2><p>
  96             <code class="function">glProvokingVertex</code> is available only if the GL version is 3.2 or greater.
  97         </p></div><div class="refsect1" title="Errors"><a id="errors"></a><h2>Errors</h2><p>
  98             <code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>provokeMode</code></em> is not an accepted value.
  99         </p></div><div class="refsect1" title="Copyright"><a id="Copyright"></a><h2>Copyright</h2><p>
 100             Copyright <span class="trademark"></span>© 2010 Khronos Group.
 101             This material may be distributed subject to the terms and conditions set forth in
 102             the Open Publication License, v 1.0, 8 June 1999.
 103             <a class="ulink" href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
 104         </p></div></div></body></html>