Ruby implementation of a simple cellular automata simulator. Gosu is used just for drawing, the CellMap class doesn't have any gosu specific code so it's very portable. Following this tutorial: http://gamedevelopment.tutsplus.com/tutorials/cave-levels-cellular-automata--gamedev-9664

Cellmap.rb

require 'gosu'

class CellMap
  include Enumerable

  def initialize(x, y, chance_to_start_alive)
    @map = Array.new
    a = Random.new()
    x.times do
      column = Array.new(y)
      y.times do |index|
        if a.rand() < chance_to_start_alive
          column[index] = true
        end
      end
      @map << column
    end
  end

  def count_alive_neighbours(x, y)
    count = 0
    (-1..1).each do |i|
      (-1..1).each do |j|
        neighbour_x = x + i
        neighbour_y = y + j
        if i == 0 and j == 0
        elsif neighbour_x < 0 or neighbour_y < 0 or neighbour_x >= @map.length or neighbour_y >= @map[0].length
          count += 1
        elsif @map[neighbour_x][neighbour_y] == true
          count += 1
        end
      end
    end
    return count
  end

  def do_simulation_step(death_limit = 4, birth_limit = 4)
    new_map = []
    @map.length.times do |x|
      new_row = []
      @map[0].length.times do |y|
        nbs = count_alive_neighbours(x, y)
        if @map[x][y]
          if nbs < death_limit
            new_row << false
          else
            new_row << true
          end
        else
          if nbs > birth_limit
            new_row << true
          else
            new_row << false
          end
        end
      end
      new_map << new_row
    end
    @map = new_map
  end

  def [](y)
    @map[y]
  end

  def height
    return @map.length
  end

  def width
    return @map[0].length
  end

end

class GameWindow < Gosu::Window

  def initialize
    super 1920, 1080, false
    @width = 300
    @height = 300
    @chance_to_start_alive = 0.45
    @cellmap = CellMap.new(@width, @height, @chance_to_start_alive)
    @last_step = Gosu::milliseconds
  end

  def update
    if button_down? Gosu::KbSpace and Gosu::milliseconds - @last_step > 100
      @last_step = Gosu::milliseconds
      @cellmap.do_simulation_step
      puts "one step close to the edge, I'm about to break!"
    elsif button_down? Gosu::KbEscape
      puts "new map"
      @cellmap = CellMap.new(@width, @height, @chance_to_start_alive)
    end
  end

  def draw_cell(x, y, width, height)
    color = Gosu::Color::WHITE
    x += x * height
    y += y * width
    draw_quad(x , y, color, 
              x, y + width, color,
              x + height, y, color,
              x + height, y + width, color)
  end

  def draw
    @cellmap.height.times do |index_x|
      @cellmap.width.times do |index_y|
        if @cellmap[index_x][index_y] == true
          draw_cell(index_x, index_y, 2, 2)
        end
      end
    end
  end
  
end

window = GameWindow.new
window.show