upstream-man-pages/manglsl/gl_Position.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="gl_Position">
   5     <refmeta>
   6         <refmetainfo>
   7             <copyright>
   8                 <year>2011</year>
   9                 <holder>Khronos Group</holder>
  10             </copyright>
  11         </refmetainfo>
  12         <refentrytitle>gl_Position</refentrytitle>
  13         <manvolnum>3G</manvolnum>
  14     </refmeta>
  15     <refnamediv>
  16         <refname>gl_Position</refname>
  17         <refpurpose>contains the position of the current vertex</refpurpose>
  18     </refnamediv>
  19     <refsynopsisdiv><title>Declaration</title>
  20         <para>
  21             <function>gl_Position</function> is a member of the <function>gl_PerVertex</function>
  22             named block:
  23         </para>
  24         <funcsynopsis>
  25 <programlisting><![CDATA[    out gl_PerVertex {
  26         vec4 gl_Position;
  27         float gl_PointSize;
  28         float gl_ClipDistance[];
  29     };]]></programlisting>
  30         </funcsynopsis>
  31     </refsynopsisdiv>
  32     <refsect1 id="description"><title>Description</title>
  33         <para>
  34             In the vertex, tessellation evaluation and geoemtry languages, a single
  35             global instance of the <function>gl_PerVertex</function> named block is available and
  36             its <function>gl_Position</function> member is an output that receives the
  37             homogeneous vertex position. It may be written at any time during shader execution.
  38             The value written to <function>gl_Position</function> will be used by primitive assembly,
  39             clipping, culling and other fixed functionality operations, if present, that operate on
  40             primitives after vertex processing has occurred.
  41         </para>
  42         <para>
  43             In the tessellation control language, the <function>gl_PerVertex</function> named block
  44             is used to construct an array, <function>gl_out[]</function>, whose <function>gl_Position</function>
  45             members hold the homogeneous control point position, which become available as inputs to the subsequent
  46             tessellation evaluation shader.
  47         </para>
  48         <para>
  49             The value of <function>gl_Position</function> (or the <function>gl_Position</function> member of the <function>gl_out[]</function>
  50             array, in the case of the tessellation control shader)
  51             is undefined after the vertex, tessellation control, and tessellation evaluation
  52             shading stages if the corresponding shader executable does
  53             not write to gl_Position. It is also undefined after the geometry processing stage if the geometry shader executable calls
  54             <citerefentry><refentrytitle>EmitVertex</refentrytitle></citerefentry> without having
  55             written <function>gl_Position</function> since the last call to <citerefentry><refentrytitle>EmitVertex</refentrytitle></citerefentry>
  56             (or hasn't written it at all).
  57         </para>
  58         <para>
  59             In the tessellation control, tessellation evaluation and geoemetry languages,
  60             the <function>gl_PerVertex</function> named block is used to construct an array, <function>gl_in[]</function>
  61             of per-vertex or per-control point inputs whose content represents the corresponding
  62             outputs written by the previous stage.
  63          </para>
  64     </refsect1>
  65     <refsect1 id="versions"><title>Version Support</title>
  66         <informaltable frame="topbot">
  67             <tgroup cols="3" align="left">
  68                 <colspec colwidth="1.1*" />
  69                 <colspec colwidth="1*" align="center" />
  70                 <colspec colwidth="1*" align="center" />
  71                 <colspec colwidth="1*" align="center" />
  72                 <colspec colwidth="1*" align="center" />
  73                 <colspec colwidth="1*" align="center" />
  74                 <colspec colwidth="1*" align="center" />
  75                 <colspec colwidth="1*" align="center" />
  76                 <colspec colwidth="1*" align="center" />
  77                 <thead>
  78                     <row>
  79                         <entry rowsep="1" align="left"><emphasis role="bold">
  80                         Variable
  81                         </emphasis></entry>
  82                         <entry rowsep="1" align="left"><emphasis role="bold">
  83                         Version 1.10
  84                         </emphasis></entry>
  85                         <entry rowsep="1" align="left"><emphasis role="bold">
  86                         Version 1.20
  87                         </emphasis></entry>
  88                         <entry rowsep="1" align="left"><emphasis role="bold">
  89                         Version 1.30
  90                         </emphasis></entry>
  91                         <entry rowsep="1" align="left"><emphasis role="bold">
  92                         Version 1.40
  93                         </emphasis></entry>
  94                         <entry rowsep="1" align="left"><emphasis role="bold">
  95                         Version 1.50
  96                         </emphasis></entry>
  97                         <entry rowsep="1" align="left"><emphasis role="bold">
  98                         Version 3.30
  99                         </emphasis></entry>
 100                         <entry rowsep="1" align="left"><emphasis role="bold">
 101                         Version 4.00
 102                         </emphasis></entry>
 103                         <entry rowsep="1" align="left"><emphasis role="bold">
 104                         Version 4.10
 105                         </emphasis></entry>
 106                     </row>
 107                     <row>
 108                         <entry>
 109                             gl_Position
 110                         </entry>
 111                         <entry>
 112                             <emphasis>Y</emphasis><superscript>1</superscript>  <!-- 1.10, OpenGL 2.0 -->
 113                         </entry>
 114                         <entry>
 115                             <emphasis>Y</emphasis><superscript>1</superscript>  <!-- 1.20, OpenGL 2.1 -->
 116                         </entry>
 117                         <entry>
 118                             <emphasis>Y</emphasis><superscript>1</superscript>  <!-- 1.30, OpenGL 3.0 -->
 119                         </entry>
 120                         <entry>
 121                             <emphasis>Y</emphasis><superscript>1</superscript>  <!-- 1.40, OpenGL 3.1 -->
 122                         </entry>
 123                         <entry>
 124                             <emphasis>Y</emphasis><superscript>2</superscript>  <!-- 1.50, OpenGL 3.2 -->
 125                         </entry>
 126                         <entry>
 127                             <emphasis>Y</emphasis><superscript>2</superscript>  <!-- 3.30, OpenGL 3.3 -->
 128                         </entry>
 129                         <entry>
 130                             <emphasis>Y</emphasis>  <!-- 4.00, OpenGL 4.0 -->
 131                         </entry>
 132                         <entry>
 133                             <emphasis>Y</emphasis>  <!-- 4.10, OpenGL 4.1 -->
 134                         </entry>
 135                     </row>
 136                 </thead>
 137             </tgroup>
 138         </informaltable>
 139         <para>Versions 1.10 to 1.40 - vertex shader only.</para>
 140         <para>Versions 1.50 to 3.30 - vertex and geometry shaders only.</para>
 141     </refsect1>
 142     <refsect1 id="seealso"><title>See Also</title>
 143         <para>
 144             <citerefentry><refentrytitle>gl_PointSize</refentrytitle></citerefentry>, <citerefentry><refentrytitle>gl_ClipDistance</refentrytitle></citerefentry>
 145         </para>
 146     </refsect1>
 147     <refsect1 id="Copyright"><title>Copyright</title>
 148         <para>
 149             Copyright <trademark class="copyright"></trademark> 2011 Khronos Group.
 150             This material may be distributed subject to the terms and conditions set forth in
 151             the Open Publication License, v 1.0, 8 June 1999.
 152             <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
 153         </para>
 154     </refsect1>
 155 </refentry>