A Sierpinski Variant using L-Systems and ruby processing

A Sierpinski (triangle) variant after Mark Meyers nodebox l-systems...
for the grammar library see a previous post Cesàro fractal


##
# A Sierpinski Variant implemented using a
# Lindenmayer System in ruby-processing by Martin Prout
###
require 'sierpinski'

class Sierpinski_Test < Processing::App
  load_libraries 'grammar'

  attr_reader :sierpinski

  def setup
    size 500, 600
    @sierpinski = Sierpinski.new
    sierpinski.create_grammar 8
    no_loop
  end

  def draw
    background 0
    sierpinski.render
  end
end

############################
# sierpinski.rb
###########################
class Sierpinski
  include Processing::Proxy

  attr_accessor :axiom, :grammar, :start_length, :theta, :production, :draw_length, :xpos, :ypos
  DELTA = (Math::PI/180) * 60.0                 # convert degrees to radians
  GAMMA = (Math::PI/180) * 60.25              

  def initialize
    @axiom = "A"
    @grammar = Grammar.new axiom
    grammar.add_rule "A", "B+A+B"        
    grammar.add_rule "B", "A-B-A"  
    @start_length = 450
    @theta = 0.0
    @xpos = width * 0.95
    @ypos = height * 0.8
    stroke 255
    @production = axiom
    @draw_length = start_length
  end

  def render                       # NB not using affine transforms here
    repeats = 1
    production.each_char do |element|
      case element
      when 'B', 'A'                    
        line(xpos, ypos, (@xpos -= draw_length * Math.cos(theta)), (@ypos += draw_length * Math.sin(theta)))
      when '+'
        @theta += DELTA * repeats  
        repeats = 1
      when '-'
        @theta -= GAMMA * repeats  
        repeats = 1
      when '2'
        repeats = 2
      else
              puts "Character '#{element}' is not in grammar"
      end
    end
  end

  ##############################
  # create grammar from axiom and
  # rules (adjust scale)
  ##############################

  def create_grammar(gen)
    @draw_length *=  0.5**gen
    @production = grammar.generate gen
  end
end