'\" t
.\"     Title: gl_ViewportIndex
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\"      Date: 05/21/2015
.\"    Manual: [FIXME: manual]
.\"    Source: [FIXME: source]
.\"  Language: English
.\"
.TH "GL_VIEWPORTINDEX" "3G" "05/21/2015" "[FIXME: source]" "[FIXME: manual]"
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.SH "NAME"
gl_ViewportIndex \- contains the index of the viewport to be used in viewport transformation and scissoring
.SH "DECLARATION"
.PP
.nf
// In geometry shaders
.fi
.sp
out\ \&int\ \&gl_ViewportIndex\ \&;
.PP
.nf
// In fragment shaders
.fi
.sp
in\ \&int\ \&gl_ViewportIndex\ \&;
.SH "DESCRIPTION"
.PP
In the geometry language,
\fIgl_ViewportIndex\fR
is used to specify the index of the viewport to which the next primitive emitted from the shader should be drawn\&. Primitives generated by the geometry shader will undergo viewport transformation and scissor testing using the viewport transformation and scissor rectangle selected by the value of
\fIgl_ViewportIndex\fR\&. The viewport index used will come from one of the vertices in the primitive being shaded\&. However, which vertex the viewport index comes from is implementation\-defined, and so it is recommended to use the same viewport index for all vertices of a primitive\&. If a geometry shader does not assign a value to
\fIgl_ViewportIndex\fR, viewport transform and scissor rectangle zero will be used\&. If a geometry shader statically assigns a value to
\fIgl_ViewportIndex\fR
and there is a path through the shader that does not assign a value to
\fIgl_ViewportIndex\fR, the value of
\fIgl_ViewportIndex\fR
is undefined for executions of the shader that take that path\&.
.PP
In the fragment language,
\fIgl_ViewportIndex\fR
will have the same value that was written to the output variable
\fIgl_ViewportIndex\fR
in the geometry stage\&. If the geometry stage does not dynamically assign to
\fIgl_ViewportIndex\fR, the value of
\fIgl_ViewportIndex\fR
in the fragment shader will be undefined\&. If the geometry stage makes no static assignment to
\fIgl_ViewportIndex\fR, the fragment stage will read zero\&. Otherwise, the fragment stage will read the same value written by the geometry stage, even if that value is out of range\&. If a fragment shader contains a static access to
\fIgl_ViewportIndex\fR, it will count against the implementation defined limit for the maximum number of inputs to the fragment stage\&.
.SH "VERSION SUPPORT"
.TS
allbox tab(:);
lB cB s s s s s s s s s s s
lB cB cB cB cB cB cB cB cB cB cB cB cB.
T{

T}:T{
\fBOpenGL Shading Language Version\fR
T}
T{
\fBFunction Name\fR
T}:T{
\fB1\&.10\fR
T}:T{
\fB1\&.20\fR
T}:T{
\fB1\&.30\fR
T}:T{
\fB1\&.40\fR
T}:T{
\fB1\&.50\fR
T}:T{
\fB3\&.30\fR
T}:T{
\fB4\&.00\fR
T}:T{
\fB4\&.10\fR
T}:T{
\fB4\&.20\fR
T}:T{
\fB4\&.30\fR
T}:T{
\fB4\&.40\fR
T}:T{
\fB4\&.50\fR
T}
.T&
l c c c c c c c c c c c c
l c c c c c c c c c c c c.
T{
gl_ViewportIndex (geometry stage)
T}:T{
\-
T}:T{
\-
T}:T{
\-
T}:T{
\-
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}
T{
gl_ViewportIndex (fragment stage)
T}:T{
\-
T}:T{
\-
T}:T{
\-
T}:T{
\-
T}:T{
\-
T}:T{
\-
T}:T{
\-
T}:T{
\-
T}:T{
\-
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}
.TE
.sp
.SH "SEE ALSO"
.PP
\fBgl_Layer\fR()
.SH "COPYRIGHT"
.PP
Copyright
\(co
2011\-2014 Khronos Group\&. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1\&.0, 8 June 1999\&.
\m[blue]\fBhttp://opencontent\&.org/openpub/\fR\m[]\&.
.SH "COPYRIGHT"
.br
Copyright \(co 2011-2014 Khronos Group
.br