NAME

       GFA - output primitive for filling polygonal areas.

SYNOPSIS

       CALL GFA (N, X, Y)

C-BINDING SYNOPSIS

       #include <ncarg/gks.h>

       void gfill_area(const Gpoint_list *point_list);

DESCRIPTION

       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.

USAGE

       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".

ACCESS

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

SEE ALSO

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

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

COPYRIGHT

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