############################################################################
#
#	File:     sier2.icn
#
#	Subject:  Program to display the Sierpinski fractal
#
#	Author:   Ralph E. Griswold
#
#	Date:     June 24, 1994
#
############################################################################
#
#   This file is in the public domain.
#
############################################################################
#
#  This is a barebones version of a display of the Sierpinski fractal.
#  It has deliberately been left simple and free of options so that the
#  basic idea is clear and so that it can be used as the basis of
#  more capable versions.
#
#  This program is based on material given in "Chaos, Fractals,
#  and Dynamics", Robert L. Devaney, Addison-Wesley, 1990.
#
############################################################################
#
#  Requires:  Version 9 graphics
#
############################################################################
#
#  Links:  wopen
#
############################################################################

link wopen

procedure main()
   local extent, x, y, i

   extent := 300

   WOpen("label=sier", "height=" || extent, "width=" || extent) |
      stop("*** cannot open window")

   x := 20			# The results do not depend on these values
   y := 150

   every i := 1 to 100000 do {
      case ?3 of {		# Decide what to do at random
         1: {
            x /:= 2
            y /:= 2
            }
         2: {
            x /:= 2
            y := (extent + y) / 2
            }
         3: {
            x := (extent + x) / 2
            y := (extent + y) / 2
            }
         }
      if i > 1000 then DrawPoint(x, y)		# Wait until attraction
      }

   Event()

end