GLdouble valueX,
                                      GLdouble valueY,
                                      GLdouble valueZ )

PARAMETERS
       tess    Specifies the tessellation object (created with gluNewTess).

       valueX  Specifies the first component of the normal.

       valueY  Specifies the second component of the normal.

       valueZ  Specifies the third component of the normal.

DESCRIPTION
       gluTessNormal  describes  a  normal  for  a  polygon that the program is
       defining.  All input data will be projected onto a  plane  perpendicular
       to  one  of the three coordinate axes before tessellation and all output
       triangles will be oriented CCW with respect to the normal  (CW  orienta‐
       tion  can be obtained by reversing the sign of the supplied normal). For
       example, if you know that all  polygons  lie  in  the  x-y  plane,  call
       gluTessNormal(tess, 0.0, 0.0, 1.0) before rendering any polygons.

       If  the supplied normal is (0.0, 0.0, 0.0) (the initial value), the nor‐
       mal is determined as follows. The direction of the  normal,  up  to  its
       sign, is found by fitting a plane to the vertices, without regard to how
       the vertices are connected. It is expected that the input data lies  ap‐
       proximately  in the plane; otherwise, projection perpendicular to one of
       the three coordinate axes may substantially  change  the  geometry.  The
       sign  of the normal is chosen so that the sum of the signed areas of all
       input contours is nonnegative (where a CCW contour has positive area).

       The supplied normal persists until it is  changed  by  another  call  to
       gluTessNormal.

SEE ALSO
       gluTessBeginPolygon, gluTessEndPolygon

                                                              GLUTESSNORMAL(3G)