NAME

       gl_FrontFacing - indicates whether a primitive is front or back facing

DECLARATION

       in bool gl_FrontFacing ;.SH "DESCRIPTION"

       Available only in the fragment language, gl_FrontFacing is an input variable whose value
       is true 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 glFrontFace. One way to compute this area is:

       a=12 ∑ j=0 n-1 x w i y w i+1 - x w i+1 y w i

       where x w i and y w i are the x and y window coordinates of the ith vertex of the n-vertex
       polygon.

       The sign of this computation is negated when the value of GL_CLIP_ORIGIN (the clip volume
       origin, set with glClipControl()) is GL_UPPER_LEFT.

VERSION SUPPORT

       ┌───────────────┬───────────────────────────────────────────────────────────────────────────────────┐
       │               │        OpenGL Shading Language Version                                            │
       ├───────────────┼──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┤
       │Variable       │ 1.10 │ 1.20 │ 1.30 │ 1.40 │ 1.50 │ 3.30 │ 4.00 │ 4.10 │ 4.20 │ 4.30 │ 4.40 │ 4.50 │
       │Name           │      │      │      │      │      │      │      │      │      │      │      │      │
       ├───────────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┤
       │gl_FrontFacing │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │
       └───────────────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┘

SEE ALSO

       gl_FragCoord(), glClipControl()

COPYRIGHT

       Copyright © 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.
       http://opencontent.org/openpub/.

COPYRIGHT

       Copyright © 2011-2014 Khronos Group

[FIXME: source]                             07/22/2015                         GL_FRONTFACING(3G)