Paste: mandel.rb

require 'complex'


WIDTH,HEIGHT = 640,480
MAX_COLOR = 360
ZOOM_FACT = 0.8
MAX_ITERATIONS = 40
CENTER = -0.65

X_INC = WIDTH / (200000 * ZOOM_FACT)
Y_INC = HEIGHT / (150000 * ZOOM_FACT)

SAT = 0.85
VAL = 0.85

class HSV
  def initialize h, s, v
    @h,@s,@v = h,s,v
  end
  
  def hi
    (@h / 60).floor % 6
  end
  
  def f
    @h / 60 - hi
  end
  
  def p
    (1 - @s) * @v
  end
  
  def q
    (1 - f * @s) * @v
  end

  def t
    (1 - ((1 - f) * @s)) * @v
  end

  def to_rgb
    h = hi
    case h
    when 0
      [@v, t, p]
    when 1
      [q, @v, p]
    when 2
      [p, @v, t]
    when 3
      [p, q, @v]
    when 4
      [t, p ,@v]
    else
      [@v, p, q]
    end
  end
end


def scale x
  return (x * 255).to_i
end

def scale_rgb rgb
  [scale(rgb[0]),scale(rgb[1]),scale(rgb[2])]
end

def make_color_map nb_cols
  out = []
  nb_cols.times do |i|
    hsv = HSV.new((360.0 * i) / (nb_cols + 1), SAT, VAL)
    color = scale_rgb hsv.to_rgb
    out << ('' << color[0] << color[1] << color[2])
  end
  out
end

COLOR_MAP = make_color_map [MAX_ITERATIONS,MAX_COLOR].min

def c i,j
  Complex(X_INC * i + CENTER - X_INC * WIDTH / 2, Y_INC * j - Y_INC * HEIGHT / 2)
end

class Complex
  def absq
    real**2 + image**2
  end
end

def pixel c
  z = Complex(0)
  (-1..MAX_ITERATIONS).reverse_each do |i|
    z = z**2 + c
    if z.absq >= 4.0
      return i
    end
  end
  return nil
end

def color iterations
  if iterations != nil
    COLOR_MAP[iterations % COLOR_MAP.length]
  else
    return "\0\0\0"
  end
end

def render
  HEIGHT.times do |j|
    WIDTH.times do |i|
      print color pixel(c i,j)
    end
  end
end

def ppm_header
  print "P6\n#{WIDTH} #{HEIGHT}\n255\n"
end

ppm_header
render