'\" t
.\"     Title: gl_Position
.\"    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_POSITION" "3G" "05/21/2015" "[FIXME: source]" "[FIXME: manual]"
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.SH "NAME"
gl_Position \- contains the position of the current vertex
.SH "DECLARATION"
.PP
\fIgl_Position\fR
is a member of the
\fIgl_PerVertex\fR
named block:
.sp
.nf
    out gl_PerVertex {
        vec4 gl_Position;
        float gl_PointSize;
        float gl_ClipDistance[];
    };
.fi
.sp
.SH "DESCRIPTION"
.PP
In the vertex, tessellation evaluation and geometry languages, a single global instance of the
\fIgl_PerVertex\fR
named block is available and its
\fIgl_Position\fR
member is an output that receives the homogeneous vertex position\&. It may be written at any time during shader execution\&. The value written to
\fIgl_Position\fR
will be used by primitive assembly, clipping, culling and other fixed functionality operations, if present, that operate on primitives after vertex processing has occurred\&.
.PP
In the tessellation control language, the
\fIgl_PerVertex\fR
named block is used to construct an array,
\fIgl_out[]\fR, whose
\fIgl_Position\fR
members hold the homogeneous control point position, which become available as inputs to the subsequent tessellation evaluation shader\&.
.PP
The value of
\fIgl_Position\fR
(or the
\fIgl_Position\fR
member of the
\fIgl_out[]\fR
array, in the case of the tessellation control shader) is undefined after the vertex, tessellation control, and tessellation evaluation shading stages if the corresponding shader executable does not write to gl_Position\&. It is also undefined after the geometry processing stage if the geometry shader executable calls
\fBEmitVertex\fR()
without having written
\fIgl_Position\fR
since the last call to
\fBEmitVertex\fR()
(or hasn\*(Aqt written it at all)\&.
.PP
In the tessellation control, tessellation evaluation and geometry languages, the
\fIgl_PerVertex\fR
named block is used to construct an array,
\fIgl_in[]\fR
of per\-vertex or per\-control point inputs whose content represents the corresponding outputs written by the previous 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.
T{
gl_Position
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
.PP
Versions 1\&.10 to 1\&.40 \- vertex shader only\&.
.PP
Versions 1\&.50 to 3\&.30 \- vertex and geometry shaders only\&.
.SH "SEE ALSO"
.PP
\fBgl_PointSize\fR(),
\fBgl_ClipDistance\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