GFA - output primitive for filling polygonal areas.

       To use GKS routines, load the NCAR GKS-0A library ncarg_gks.

       #include <ncarg/gks.h>

       void gfill_area(const Gpoint_list *point_list);

       Copyright (C) 1987-2009
       University Corporation for Atmospheric Research
       The use of this Software is governed by a License Agreement.

UNIX                                               March 1993                                        GFA(3NCARG)

       N           (Integer,  Input) - The number of points in the polygon to be filled.  N must be greater than
                   two.

       X (N)       (Real Array, Integer) - The X world coordinates of the polygon.

       Y (N)       (Real Array, Integer) - The Y world coordinates of the polygon.

       GFA - output primitive for filling polygonal areas.

       Online: gsfais, gsfasi, gscr, gsfaci, gqfais, gqfasi, gfill_area

       Hardcopy: User's Guide for NCAR GKS-0A Graphics; NCAR Graphics Fundamentals, UNIX Version

       CALL GFA (N, X, Y)

       The area to be filled is delimited by the sequence of straight line segments  connecting  the  successive
       points   (X(1), Y(1)), (X(2), Y(2)), ..., (X(N), Y(N)). The last point in the polygon is connected to the
       first point with a straight line segment in the case that (X(N), Y(N)) does not equal (X(l), Y(l)).

       Given a polygon whose edges cross each other, it becomes ambiguous as to what constitutes the "inside" of
       the polygon.  The algorithm used in GKS is as follows: for a given point, draw a  ray  starting  at  that
       point  and  going  to  infinity  in any direction; if the number of intersections between the ray and the
       polygon is odd, the point is within the polygon, otherwise it is outside.  If the  straight  line  passes
       through  a polygon vertex tangentially, the intersection count is not affected.  If a point is within the
       polygon, it is included in the area to be filled.

       Several interior styles (hollow, solid, and various hatch patterns) can be selected.  See the  man  pages
       for gsfais and gsfasi for these.

       Note  well:  By default in GKS, the interior fill style is hollow, or no fill. If you call GFA and do not
       get a filled interior as you expected, you will probably need to call GSFAIS to set  the  fill  style  to
       something other than "hollow".