GL_FRONTFACING(3G)

    .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, 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:
        .PP a=12 ∑ i=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 ith vertex of the n-vertex polygon.

    .SH "VERSION SUPPORT"
        .TS allbox tab(:); l l l l l. T{ gl_FrontFacing T}:T{ T}:T{ T}:T{ T}:T{ T}

    .SH "SEE ALSO"
        .PP gl_FragCoord()

    .SH "COPYRIGHT"
        .PP Copyright © 2011-2015 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 © 2011-2015 Khronos Group