Name:         GRFA

Purpose:      fill area (polygon)

Category:     GRAPHICS

File:         pgplot.src

Author:       T.J. Pearson

Use:          see description below.

Description:

            SUBROUTINE GRFA (N,PX,PY)
            INTEGER N
            REAL PX(*), PY(*)
      
       GRPCKG: FILL AREA: fill a polygon with solid color.  The polygon
       is defined by the (x,y) world coordinates of its N vertices.  If
       this is not a function supported by the device, shading is
       accomplished by drawing horizontal lines spaced by 1 pixel.  By
       selecting color index 0, the interior of the polygon can be erased
       on devices which permit it.  The polygon need not be convex, but if
       it is re-entrant (i.e., edges intersect other than at the vertices),
       it may not be obvious which regions are "inside" the polygon.  The
       following rule is applied: for a given point, create a straight line
       starting at the point and going to infinity. If the number of
       intersections between the straight line and the polygon is odd, the
       point is within the polygon; otherwise it is outside. If the
       straight line passes a polygon vertex tangentially, the
       intersection  count is not affected. The only attribute which applies
       to FILL AREA is color index: line-width and line-style are ignored.
       There is a limitation on the complexity of the polygon: GFA will
       fail if any horizontal line intersects more than 32 edges of the
       polygon.
      
       Arguments:
      
       N (input, integer): the number of vertices of the polygon (at least
             3).
       PX, PY (input, real arrays, dimension at least N): world coordinates
             of the N vertices of the polygon.

Updates:      Oct 16, 1998: JPT automatically extracted from source.