Name:         GRPOCL

Purpose:      polygon clip

Category:     GRAPHICS

File:         pgplot.src

Author:       T.J. Pearson

Use:          see description below.

Description:

            SUBROUTINE GRPOCL (N,PX,PY, EDGE, VAL, MAXOUT, NOUT, QX, QY)
            INTEGER N, NOUT, EDGE, MAXOUT
            REAL    PX(*), PY(*), QX(*), QY(*)
            REAL    VAL
      
       Clip a polygon against a rectangle: Sutherland-Hodgman algorithm.
       this routine must be called four times to clip against each of the
       edges of the rectangle in turn.      
      
       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 input polygon.
       EDGE (input, integer):
           1: clip against left edge,   X > XMIN=VAL
           2: clip against right edge,  X < XMAX=VAL
           3: clip against bottom edge, Y > YMIN=VAL
           4: clip against top edge,    Y < YMIN=VAL
       VAL  (input, real): coordinate value of current edge.
       MAXOUT (input, integer): maximum number of vertices allowed in
           output polygon (dimension of QX, QY).
       NOUT (output, integer): the number of vertices in the clipped polygon.
       QX, QY (output, real arrays, dimension at least MAXOUT): world
             coordinates of the NOUT vertices of the output polygon.

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