fgluTessNormal(3G)

NAME
     fgluTessNormal - specify a normal for a polygon


FORTRAN SPECIFICATION
     SUBROUTINE fgluTessNormal( CHARACTER*8 tess,
                                REAL*4 valueX,
                                REAL*4 valueY,
                                REAL*4 valueZ )


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

     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
     fgluTessNormal 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 orientation
     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
     fgluTessNormal(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 normal
     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
     approximately 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
     fgluTessNormal.

SEE ALSO
     fgluTessBeginPolygon, fgluTessEndPolygon