upstream-doc/manglsl/gl_PrimitiveID.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_PrimitiveID">
   5     <refmeta>
   6         <refmetainfo>
   7             <copyright>
   8                 <year>2011</year>
   9                 <holder>Khronos Group</holder>
  10             </copyright>
  11         </refmetainfo>
  12         <refentrytitle>gl_PrimitiveID</refentrytitle>
  13         <manvolnum>3G</manvolnum>
  14     </refmeta>
  15     <refnamediv>
  16         <refname>gl_PrimitiveID</refname>
  17         <refpurpose>contains the index of the current primitive</refpurpose>
  18     </refnamediv>
  19     <refsynopsisdiv><title>Declaration</title>
  20         <funcsynopsis>
  21             <function>in int gl_PrimitiveID;</function> (Tessellation control, tessellation evaluation and fragment languages)<sbr/>
  22             <function>out int gl_PrimitiveID;</function> (Geometry language)
  23         </funcsynopsis>
  24     </refsynopsisdiv>
  25     <refsect1 id="description"><title>Description</title>
  26         <para>
  27             <function>gl_PrimitiveID</function> is a tessellation control, tessellation evaluation
  28             and fragment language input variable. For the tessellation control and tessellation
  29             evaluation languages, it holds the number of primitives processed by
  30             the shader since the current set of rendering primitives was started. The first
  31             primitive processed by the drawing command is numbered zero and the primitive ID counter is incremented after every individual point, line
  32             or triangle primitive is processed. For triangles drawn in point or line mode, the
  33             primitive ID counter is incremented only once, even through multiple points or lines
  34             may actually be drawn. Restarting a primitive topology using the primitive restart
  35             index has no effect on the primitive ID counter.
  36         </para>
  37         <para>
  38             In the geometry language, <function>gl_PrimitiveID</function> is an output
  39             variable that is passed to the corresponding <function>gl_PrimitiveID</function> input
  40             variable in the fragment shader. If no geomery shader is present then <function>gl_PrimitiveID</function>
  41             in the fragment language behaves identically as it would in the tessellation control and evaluation
  42             languages. If a geometry shader is present but does not write to <function>gl_PrimitiveID</function>,
  43             the value of <function>gl_PrimitiveID</function> in the fragment shader is undefined.
  44         </para>
  45     </refsect1>
  46     <refsect1 id="versions"><title>Version Support</title>
  47         <informaltable frame="topbot">
  48             #VARTABLECOLS#
  49                 <thead>
  50                     #FUNCTABLEHEADER#
  51                     <row>
  52                         <entry><function>gl_PrimitiveID</function> (Fragment and Geometry Languages)</entry>#newin15#
  53                     </row>
  54                     <row>
  55                         <entry><function>gl_PrimitiveID</function> (Tessellation Control and Evaluation Languages)</entry>#newin40#
  56                     </row>
  57                 </thead>
  58             </tgroup>
  59         </informaltable>
  60     </refsect1>
  61     <refsect1 id="seealso"><title>See Also</title>
  62         <para>
  63             <citerefentry><refentrytitle>gl_InstanceID</refentrytitle></citerefentry>,
  64             <citerefentry><refentrytitle>gl_VertexID</refentrytitle></citerefentry>,
  65             <citerefentry><refentrytitle>gl_PrimitiveIDIn</refentrytitle></citerefentry>
  66         </para>
  67     </refsect1>
  68     <refsect1 id="Copyright"><title>Copyright</title>
  69         <para>
  70             Copyright <trademark class="copyright"></trademark> 2011 Khronos Group.
  71             This material may be distributed subject to the terms and conditions set forth in
  72             the Open Publication License, v 1.0, 8 June 1999.
  73             <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
  74         </para>
  75     </refsect1>
  76 </refentry>