%mathent; ]> 2011-2014 Khronos Group gl_FrontFacing 3G gl_FrontFacing indicates whether a primitive is front or back facing in bool gl_FrontFacing 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. gl_FrontFacing gl_FragCoord 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/.