From: Morton Goldberg <m_goldberg@...>
Date: 2007-05-28T00:35:50+09:00
Subject: Re: [QUIZ] Fractals (#125) [SOLUTION]

Here is my solution to Quiz 125.

Since the required fractal is a recursive turtle path, the Turtle  
Geometry kit developed for Quiz 104 can be used to provide a short  
and simple solution to this quiz.

<code>
#  Created by Morton Goldberg on May 26, 2007.
#  quiz_125_fractal.rb

def fractal(n, s)
    if n == 0
       forward s
    else
       fractal(n-1, s/3.0)
       left 90
       fractal(n-1, s/3.0)
       right 90
       fractal(n-1, s/3.0)
       right 90
       fractal(n-1, s/3.0)
       left 90
       fractal(n-1, s/3.0)
    end
end

USAGE = <<MSG
Usage:  turtle_viewer.rb quiz_125_fractal.rb [level]
\twhere level is a single digit integer
\trecommend level be less than 6
MSG

n = case ARGV[0]
     when nil then 3 # show level 3 if no argument given
     when /^\d$/ then ARGV[0].to_i
     else
        puts USAGE
        exit
     end
go [-190, -100]
right 90
pen_down
fractal(n, 380)
</code>

The turtle_viewer.rb script, also developed for Quiz 104 can run the  
above turtle program and produce the desired graphic output. But  
there is a problem. The turtle program wants a command line parameter  
and turtle_viewer.rb, without modification, doesn't make provision  
for this. Not to worry -- changing one line in turtle_viewer.rb fixes  
it up.

<code>
#! /usr/bin/env ruby -w
#  Created by Morton Goldberg on November 02, 2006.
#  Modified on November 17, 2006
#  Modified on May 26, 2007
#  turtle_viewer.rb

ROOT_DIR = File.dirname(__FILE__)
$LOAD_PATH << File.join(ROOT_DIR, "lib")

require 'tk'
require 'turtle_view'
require 'turtle'

# A simple Ruby/Tk script for viewing turtle graphics.
#
# If a file path is supplied as the first command line argument, the
# file is taken as the source for the turtle program to be run. If no
# argument is given, a default turtle program (CIRCLE_DESIGN -- see
# below) is run.

class TurtleViewer
    def initialize(code)
       @code = code
       # Create and lay out the viewer. Its only widget is a canvas.
       root = TkRoot.new {
          bg "DodgerBlue2"
          title "Turtle Graphics Viewer"
          }
       @canvas = TkCanvas.new(root) {
          relief :solid
          borderwidth 1
       }
       @canvas.pack(:fill=>:both, :expand=>true, :padx=>20, :pady=>20)
       # Run turtle commands when the canvas is mapped by Tk.
       @canvas.bind('Map') { run_code }
       # Set the window geometry; i.e., size and placement.
       win_w, win_h = 440, 440
       win_x = (root.winfo_screenwidth - win_w) / 2
       root.geometry("#{win_w}x#{win_h}+#{win_x}+50")
       root.resizable(false, false)
       # Make Cmnd+Q work as expected on Moc OS X.
       root.bind('Command-q') { Tk.root.destroy }
    end

    def run_code
       turtle = Turtle.new
       view = TurtleView.new(turtle, @canvas)
       view.handle_map_event(TkWinfo.width(@canvas),
                             TkWinfo.height(@canvas))
       turtle.run(@code)
       view.draw
    end
end

# Commands to be run if no command line argument is given.
CIRCLE_DESIGN = <<CODE
def circle
    pd; 90.times { fd 6; rt 4 }; pu
end
18.times { circle; rt 20 }
CODE

if ARGV.size > 0
    code = open(ARGV.shift) { |f| f.read }  # **** modified ****
else
    code = CIRCLE_DESIGN
end
TurtleViewer.new(code)
Tk.mainloop
</code>

Regards, Morton