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 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	✔	✔	✔	✔	✔	✔	✔	✔	✔	✔	✔	✔

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. m[blue]http://opencontent.org/openpub/m[].

COPYRIGHT

Copyright © 2011-2014 Khronos Group