############################################################################
#
#	File:     moire.icn
#
#	Subject:  Program to display Moire patterns
#
#	Author:   Ralph E. Griswold
#
#	Date:     May 2, 2001
#
############################################################################
#
#   This file is in the public domain.
#
############################################################################
#
#  This program displays moire patterns.
#
#  The following options are supported:
#
#	-g	run continuously; ignore user events; default: process user
#		  events
#	-i i	initial size, default 50
#	-k i	increment, default 1
#	-l i	limit on number of iterations, default 2 ^ 10
#	-p s	palette, default "c2"
#	-s i	size of window (width/height); default 256
#
#  This program is based on material given in "FractalVision",
#  Dick Oliver, Sams Publishing, 1992, pp. 185-190.
#
############################################################################
#
#  Requires:  Version 9 graphics
#
############################################################################
#
#  Links:  colrlist, interact, options, wopen
#
############################################################################

link colrlist
link interact
link options
link wopen

procedure main(args)
   local extent, size, colors, ncolors, k, x, i, y, j, c, palette
   local opts, init, incr, limit, run

   opts := options(args, "gs+p:i+k+l+")

   palette := \opts["p"] | "c2"
   extent := \opts["s"] | 256
   init := \opts["i"] | 50
   incr := \opts["k"] | 1
   limit := \opts["l"] | (2 ^ 10)
   run := opts["g"]

   size := extent / 2

   WOpen("label=moire", "height=" || extent, "width=" || extent,
      "dx=" ||  size, "dy=" || size, "bg=light gray") |
         ExitNotice("Cannot open window.")

   colors := colrplte(palette) | ExitNotice("Invalid palette.")
   ncolors := *colors

   every k := seq(init, incr) \ limit do {
      x := k
      every i := 0 to size do {
         y := x
         every j := i to size do {
            c := colors[?ncolors]
            Fg(c)
            DrawPoint(
               i, j,
               j, i,
               j, -i,
               i, -j,
               -i, -j,
               -j, -i,
               -j, i,
               -i, j
               )
            y +:= k
            }
         x +:= k
         }
      Fg("black")
      if /run then repeat case Event() of {
         "q":   exit()
         "s":   snapshot()
         "n":   break
         }
      }

end