--- /dev/null
+<?xml version="1.0" encoding="UTF-8"?>\r
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"\r
+ "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">\r
+<refentry id="gl_ClipDistance">\r
+ <refmeta>\r
+ <refmetainfo>\r
+ <copyright>\r
+ <year>2011</year>\r
+ <holder>Khronos Group</holder>\r
+ </copyright>\r
+ </refmetainfo>\r
+ <refentrytitle>gl_ClipDistance</refentrytitle>\r
+ <manvolnum>3G</manvolnum>\r
+ </refmeta>\r
+ <refnamediv>\r
+ <refname>gl_ClipDistance</refname>\r
+ <refpurpose>provides a forward-compatible mechanism for vertex clipping</refpurpose>\r
+ </refnamediv>\r
+ <refsynopsisdiv><title>Declaration</title>\r
+ <para>\r
+ <function>gl_ClipDistance</function> is a member of the <function>gl_PerVertex</function>\r
+ named block:\r
+ </para>\r
+ <funcsynopsis>\r
+<programlisting><![CDATA[ out gl_PerVertex {\r
+ vec4 gl_Position;\r
+ float gl_PointSize;\r
+ float gl_ClipDistance[];\r
+ };]]></programlisting>\r
+ </funcsynopsis>\r
+ <para>\r
+ In the fragment language, it is intrinsically declared as:\r
+ </para>\r
+ <funcsynopsis>\r
+ <function>in float gl_ClipDistance[];</function>\r
+ </funcsynopsis>\r
+ </refsynopsisdiv>\r
+ <refsect1 id="description"><title>Description</title>\r
+ <para>\r
+ The <function>gl_ClipDistance</function> variable provides a forward compatible\r
+ mechanism for controlling user clipping. The element <function>gl_ClipDistance[<emphasis>i</emphasis>]</function>\r
+ specifies a clip distance for each user clip plane <emphasis>i</emphasis>. A distance of 0.0 means that\r
+ the vertex is on the plane, a positive distance means that the vertex is insider the clip plane, and a negative\r
+ distance means that the point is outside the clip plane. The clip distances will be linearly interpolated across\r
+ the primitive and the portion of the primitive with interpolated distances less than 0.0 will be clipped.\r
+ </para>\r
+ <para>\r
+ The <function>gl_ClipDistance</function> array is initially predeclared as unsized and must be\r
+ sized by the shader either by redeclaring it with an explicit size, or by indexing it\r
+ with only integral constant expressions. The array must be sized to include all\r
+ clip planes that are enabled via the OpenGL API; if the size does not include all enabled planes,\r
+ results are undefined. The size may be at most <function>gl_MaxClipDistances</function>. The number\r
+ of variing components consumed by <function>gl_ClipDistance</function> will match the size of the\r
+ array, no matter how many planes are enabled. The shader must also set all values in <function>gl_ClipDistance</function>\r
+ that have been enabled via the OpenGL API, or results are undefined. Values written into\r
+ <function>gl_ClipDistance</function> planes that are not enabled have no effect.\r
+ </para>\r
+ <para>\r
+ In the vertex, tessellation evaluation and geoemtry languages, a single\r
+ global instance of the <function>gl_PerVertex</function> named block is available and\r
+ its <function>gl_ClipDistance</function> member is an output that receives the\r
+ clip distances for the current vertex. It may be written at any time during shader execution.\r
+ The value written to <function>gl_ClipDistance</function> will be used by primitive assembly,\r
+ clipping, culling and other fixed functionality operations, if present, that operate on\r
+ primitives after vertex processing has occurred.\r
+ </para>\r
+ <para>\r
+ In the tessellation control language, the <function>gl_PerVertex</function> named block\r
+ is used to construct an array, <function>gl_out[]</function>, whose <function>gl_ClipDistance</function>\r
+ members hold clip distances for each of the control points, which become available as inputs to the subsequent\r
+ tessellation evaluation shader.\r
+ </para>\r
+ <para>\r
+ The value of <function>gl_ClipDistance</function> (or the <function>gl_ClipDistance</function> member of the <function>gl_out[]</function>\r
+ array, in the case of the tessellation control shader)\r
+ is undefined after the vertex, tessellation control, and tessellation evaluation\r
+ shading stages if the corresponding shader executable does\r
+ not write to gl_ClipDistance. It is also undefined after the geometry processing stage if the geometry shader executable calls\r
+ <citerefentry><refentrytitle>EmitVertex</refentrytitle></citerefentry> without having\r
+ written <function>gl_ClipDistance</function> since the last call to <citerefentry><refentrytitle>EmitVertex</refentrytitle></citerefentry>\r
+ (or hasn't written it at all).\r
+ </para>\r
+ <para>\r
+ In the tessellation control, tessellation evaluation and geoemetry languages,\r
+ the <function>gl_PerVertex</function> named block is used to construct an array, <function>gl_in[]</function>\r
+ of per-vertex or per-control point inputs whose content represents the corresponding\r
+ outputs written by the previous stage. Only elements of the <function>gl_ClipDistance</function>\r
+ array that correspond to enabled clip planes have defined values.\r
+ </para>\r
+ </refsect1>\r
+ <refsect1 id="versions"><title>Version Support</title>\r
+ <informaltable frame="topbot">\r
+ #VARTABLECOLS#\r
+ <thead>\r
+ #VARTABLEHEADER#\r
+ <row>\r
+ <entry>gl_ClipDistance</entry>#newin13#\r
+ </row>\r
+ </thead>\r
+ </tgroup>\r
+ </informaltable>\r
+ <para>Versions 1.30 to 1.40 - vertex shader only.</para>\r
+ <para>Versions 1.50 to 3.30 - vertex and geometry shaders only.</para>\r
+ </refsect1>\r
+ <refsect1 id="seealso"><title>See Also</title>\r
+ <para>\r
+ <citerefentry><refentrytitle>gl_PointSize</refentrytitle></citerefentry>\r
+ </para>\r
+ </refsect1>\r
+ <refsect1 id="Copyright"><title>Copyright</title>\r
+ <para>\r
+ Copyright <trademark class="copyright"></trademark> 2011 Khronos Group. \r
+ This material may be distributed subject to the terms and conditions set forth in \r
+ the Open Publication License, v 1.0, 8 June 1999.\r
+ <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.\r
+ </para>\r
+ </refsect1>\r
+</refentry>\r
HCoop / clinton / guile-figl.git / blobdiff