1GFA(3NCARG)                      NCAR GRAPHICS                     GFA(3NCARG)
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NAME

6       GFA (Fill area) - output primitive for filling polygonal areas.
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SYNOPSIS

9       CALL GFA (N, X, Y)
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C-BINDING SYNOPSIS

12       #include <ncarg/gks.h>
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14       void gfill_area(const Gpoint_list *point_list);
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DESCRIPTION

17       N           (Integer,  Input)  - The number of points in the polygon to
18                   be filled.  N must be greater than two.
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20       X (N)       (Real Array, Integer) - The  X  world  coordinates  of  the
21                   polygon.
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23       Y (N)       (Real  Array,  Integer)  -  The  Y world coordinates of the
24                   polygon.
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USAGE

27       The area to be filled is delimited by the  sequence  of  straight  line
28       segments  connecting the successive points  (X(1), Y(1)), (X(2), Y(2)),
29       ..., (X(N), Y(N)). The last point in the polygon is  connected  to  the
30       first  point with a straight line segment in the case that (X(N), Y(N))
31       does not equal (X(l), Y(l)).
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33       Given a polygon whose edges cross each other, it becomes  ambiguous  as
34       to what constitutes the "inside" of the polygon.  The algorithm used in
35       GKS is as follows: for a given point, draw a ray starting at that point
36       and  going to infinity in any direction; if the number of intersections
37       between the ray and the polygon is odd, the point is within  the  poly‐
38       gon,  otherwise  it  is outside.  If the straight line passes through a
39       polygon vertex tangentially, the intersection count  is  not  affected.
40       If  a  point  is  within  the polygon, it is included in the area to be
41       filled.
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43       Several interior styles (hollow, solid, and various hatch patterns) can
44       be selected.  See the man pages for gsfais and gsfasi for these.
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46       Note  well: By default in GKS, the interior fill style is hollow, or no
47       fill. If you call GFA and do not get a filled interior as you expected,
48       you  will  probably  need to call GSFAIS to set the fill style to some‐
49       thing other than "hollow".
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ACCESS

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

55       Online: gsfais, gsfasi, gscr, gsfaci, gqfais, gqfasi, gfill_area
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57       Hardcopy: User's Guide for NCAR GKS-0A Graphics; NCAR  Graphics  Funda‐
58       mentals, UNIX Version
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61       Copyright (C) 1987-2009
62       University Corporation for Atmospheric Research
63       The use of this Software is governed by a License Agreement.
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67UNIX                              March 1993                       GFA(3NCARG)
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