From: Matthias Reitinger <reitinge@...>
Date: 2009-03-25T07:04:37+09:00
Subject: Re: Midpoint Displacement (#197)

Di Mo wrote:
> ## Midpoint Displacement (#197)

My solution utilizes Builder to print a SVG representation to stdout. 
Note that the enum_for(:each_cons, 2) construct could be replaced by a 
simple each_cons(2) when running Ruby 1.8.7 or 1.9.x.

  #!/usr/bin/env ruby

  require 'rubygems'
  require 'builder'
  require 'enumerator'

  # Options
  max_offset = 0.5
  roughness = 0.5
  iterations = 12
  width = height = 100
  style = "fill: black; stroke: none"

  # Midpoint displacement
  heights = [0.0, 0.0]
  iterations.times do
    heights = heights.enum_for(:each_cons, 2).map do |left, right|
      mid = (left + right) / 2
      mid += (rand * 2 - 1) * max_offset
      [left, mid]
    end.flatten << heights[-1]
    max_offset *= roughness
  end

  # SVG output
  builder = Builder::XmlMarkup.new(:target => STDOUT)
  builder.instruct!
  builder.svg(:version => "1.1", :width => width, :height => height) do 
|svg|
    xs = (0...heights.size).map {|x| x.to_f / (heights.size - 1) * 
width}
    ys = heights.map {|y| (1 - y) * height * 0.5}
    points = [0, height] + xs.zip(ys) + [width, height]
    svg.polyline(:style => style, :points => points.join(" "))
  end

-Matthias
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