GL_FRONTFACING

Section: [FIXME: manual] (3G)
Updated: 07/25/2019
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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 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 © 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


 

Index

NAME
DECLARATION
VERSION SUPPORT
SEE ALSO
COPYRIGHT
COPYRIGHT
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