GL_FRONTFACING(3G)              [FIXME: manual]             GL_FRONTFACING(3G)

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 <sum> 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 Name  | 1.10 | 1.20 | 1.30 | 1.40 | 1.50 | 3.30 | 4.00 | 4.10 | 4.20 | 4.30 | 4.40 | 4.50 |
       +---------------+------+------+------+------+------+------+------+------+------+------+------+------+
       |gl_FrontFacing | <?>  | <?>  | <?>  | <?>  | <?>  | <?>  | <?>  | <?>  | <?>  | <?>  | <?>  | <?>  |
       +---------------+------+------+------+------+------+------+------+------+------+------+------+------+

SEE ALSO
       gl_FragCoord(), glClipControl()

COPYRIGHT
       Copyright (C) 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 (C) 2011-2014 Khronos Group

[FIXME: source]                   05/21/2022                GL_FRONTFACING(3G)