'\" t
.\"     Title: gl_FrontFacing
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: 01/03/2018
.\"    Manual: [FIXME: manual]
.\"    Source: [FIXME: source]
.\"  Language: English
.\"
.TH "GL_FRONTFACING" "3G" "01/03/2018" "[FIXME: source]" "[FIXME: manual]"
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.nh
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.SH "NAME"
gl_FrontFacing \- indicates whether a primitive is front or back facing
.SH "DECLARATION"
in\ \&bool\ \&gl_FrontFacing\ \&;.SH "DESCRIPTION"
.PP
Available only in the fragment language,
\fIgl_FrontFacing\fR
is an input variable whose value is
\fBtrue\fR
if the fragment belongs to a front\-facing primitive and false otherwise\&. The determination of whether a triangle primitive is front\-facing is made by examining the sign of the area of the triangle, including a possible reversal of this sign as controlled by
\fIglFrontFace\fR\&. One way to compute this area is:
.PP
a=12 ∑ j=0 n\-1 x w i y w i+1 \- x w i+1 y w i
.PP
where
x w i
and
y w i
are the x and y window coordinates of the
\fIi\fRth vertex of the n\-vertex polygon\&.
.PP
The sign of this computation is negated when the value of
\fBGL_CLIP_ORIGIN\fR
(the clip volume origin, set with
\fBglClipControl\fR()) is
\fBGL_UPPER_LEFT\fR\&.
.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{
\fBVariable 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_FrontFacing
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 1
.SH "SEE ALSO"
.PP
\fBgl_FragCoord\fR(),
\fBglClipControl\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