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1 | <?xml version="1.0" encoding="UTF-8"?>\r |
2 | <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"\r | |
3 | "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">\r | |
4 | <refentry id="gl_ViewportIndex">\r | |
5 | <refmeta>\r | |
6 | <refmetainfo>\r | |
7 | <copyright>\r | |
8 | <year>2011</year>\r | |
9 | <holder>Khronos Group</holder>\r | |
10 | </copyright>\r | |
11 | </refmetainfo>\r | |
12 | <refentrytitle>gl_ViewportIndex</refentrytitle>\r | |
13 | <manvolnum>3G</manvolnum>\r | |
14 | </refmeta>\r | |
15 | <refnamediv>\r | |
16 | <refname>gl_ViewportIndex</refname>\r | |
17 | <refpurpose>contains the index of the viewport to be used in viewport transformation and scissoring</refpurpose>\r | |
18 | </refnamediv>\r | |
19 | <refsynopsisdiv><title>Declaration</title>\r | |
20 | <funcsynopsis>\r | |
21 | <function>out int gl_ViewportIndex; // Geometry stage</function>\r | |
22 | </funcsynopsis>\r | |
23 | <funcsynopsis>\r | |
24 | <function>in int gl_ViewportIndex; // Fragment stage</function>\r | |
25 | </funcsynopsis>\r | |
26 | </refsynopsisdiv>\r | |
27 | <refsect1 id="description"><title>Description</title>\r | |
28 | <para>\r | |
29 | In the geometry language, <function>gl_ViewportIndex</function> is used to specify the index\r | |
30 | of the viewport to which the next primitive emitted from the shader should be drawn. Primitives generated\r | |
31 | by the geometry shader will undergo viewport transformation and scissor testing using the viewport\r | |
32 | transformation and scissor rectangle selected by the value of <function>gl_ViewportIndex</function>.\r | |
33 | The viewport index used will come from one of the vertices in the primitive being shaded. However, which\r | |
34 | vertex the viewport index comes from is implementation-defined, and so it is recommended to use the same\r | |
35 | viewport index for all vertices of a primitive. If a geometry shader does not assign a value to\r | |
36 | <function>gl_ViewportIndex</function>, viewport transform and scissor rectangle zero will be used.\r | |
37 | If a geometry shader statically assigns a value to <function>gl_ViewportIndex</function> and there\r | |
38 | is a path through the shader that does not assign a value to <function>gl_ViewportIndex</function>,\r | |
39 | the value of <function>gl_ViewportIndex</function> is undefined for executions of the shader that take\r | |
40 | that path.\r | |
41 | </para>\r | |
42 | <para>\r | |
43 | In the fragment language, <function>gl_ViewportIndex</function> will have the same value that was written to the \r | |
44 | output variable <function>gl_ViewportIndex</function> in the geometry stage. If the geometry stage does not dynamically\r | |
45 | assign to <function>gl_ViewportIndex</function>, the value of <function>gl_ViewportIndex</function> in the fragment shader will be undefined. If\r | |
46 | the geometry stage makes no static assignment to <function>gl_ViewportIndex</function>, the fragment stage will read zero.\r | |
47 | Otherwise, the fragment stage will read the same value written by the geometry stage, even if that value is\r | |
48 | out of range. If a fragment shader contains a static access to <function>gl_ViewportIndex</function>, it will count against the\r | |
49 | implementation defined limit for the maximum number of inputs to the fragment stage.\r | |
50 | </para>\r | |
51 | </refsect1>\r | |
52 | <refsect1 id="versions"><title>Version Support</title>\r | |
53 | <informaltable frame="topbot">\r | |
54 | #VARTABLECOLS#\r | |
55 | <thead>\r | |
56 | #FUNCTABLEHEADER#\r | |
57 | <row>\r | |
58 | <entry>gl_ViewportIndex (geometry stage)</entry>#newin15#\r | |
59 | </row>\r | |
60 | <row>\r | |
61 | <entry>gl_ViewportIndex (fragment stage)</entry>#newin43#\r | |
62 | </row>\r | |
63 | </thead>\r | |
64 | </tgroup>\r | |
65 | </informaltable>\r | |
66 | </refsect1>\r | |
67 | <refsect1 id="seealso"><title>See Also</title>\r | |
68 | <para>\r | |
69 | <citerefentry><refentrytitle>gl_Layer</refentrytitle></citerefentry>\r | |
70 | </para>\r | |
71 | </refsect1>\r | |
72 | <refsect1 id="Copyright"><title>Copyright</title>\r | |
73 | <para>\r | |
74 | Copyright <trademark class="copyright"></trademark> 2011 Khronos Group. \r | |
75 | This material may be distributed subject to the terms and conditions set forth in \r | |
76 | the Open Publication License, v 1.0, 8 June 1999.\r | |
77 | <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.\r | |
78 | </para>\r | |
79 | </refsect1>\r | |
80 | </refentry>\r |