- define front- and back-facing polygons



C SPECIFICATION


PARAMETERS

       _param1  Specifies  the  orientation of front-facing poly-
                gons.  GL_CW and GL_CCW are accepted.   The  ini-
                tial value is GL_CCW.


DESCRIPTION

       In  a  scene  composed entirely of opaque closed surfaces,
       back-facing polygons are never visible.  Eliminating these
       invisible  polygons has the obvious benefit of speeding up
       the rendering of the image.  To enable and disable  elimi-
       nation   of   back-facing   polygons,  call  glEnable  and
       glDisable with argument GL_CULL_FACE.

       The projection of a polygon to window coordinates is  said
       to have clockwise winding if an imaginary object following
       the path from its first vertex, its second vertex, and  so
       on, to its last vertex, and finally back to its first ver-
       tex, moves in a clockwise direction about the interior  of
       the polygon.  The polygon's winding is said to be counter-
       clockwise if the imaginary object following the same  path
       moves  in  a counterclockwise direction about the interior
       of the polygon.  glFrontFace  specifies  whether  polygons
       with  clockwise winding in window coordinates, or counter-
       clockwise winding in window coordinates, are taken  to  be
       front-facing.   Passing GL_CCW to _param1 selects counter-
       clockwise polygons as front-facing; GL_CW  selects  clock-
       wise  polygons as front-facing.  By default, counterclock-
       wise polygons are taken to be front-facing.


ERRORS

       GL_INVALID_ENUM is generated if _param1 is not an accepted
       value.

       GL_INVALID_OPERATION  is  generated if glFrontFace is exe-
       cuted between the execution of glBegin and the correspond-
       ing execution of glEnd.


ASSOCIATED GETS

       glGet with argument GL_FRONT_FACE


SEE ALSO

       glCullFace, glLightModel



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