From: Michael Libby <michael.c.libby@...>
Date: 2009-03-25T01:20:20+09:00
Subject: Re: [QUIZ] Midpoint Displacement (#197)

On Fri, Mar 20, 2009 at 10:30 AM, Daniel Moore <yahivin@gmail.com> wrote:
> ## Midpoint Displacement (#197)

Here's my version. Starts with a flat line and displaces the
midpoint(s) iteratively. Iteration method takes a block so that
calling code can decide what to do with the information. In this
implementation I dump iteration info to the console and create some
pictures.

The bulk of the code is specific to RMagick and does per frame GIFs as
an animated one of the whole sequence.

Sample image at: http://www.above-average-software.com/img/line_anim.gif

#!/usr/bin/ruby -w

require 'RMagick'

def get_displaced_midpoint(left, right, range)
 mid = (left + right) / 2.0
 adj = (rand * range) * (0 == rand(2) ? -1 : 1)
 return mid + adj
end

def displace_line(line, range)
 offset = 1
 0.upto(line.length - 2) do |x|
   line.insert(x + offset, get_displaced_midpoint(line[x + offset -
1], line[x + offset], range))
   offset += 1
 end
 return line
end

def draw_line(iter, line, range, width, height, anim_list)
 drawing = Magick::Draw.new
 x_factor = width / (line.count - 1)
 0.upto(line.count - 2) do |x|
   drawing.line x_factor * x, (height/2) - (height * line[x] / 2),
x_factor * (x + 1), (height / 2) - (height * line[x + 1] / 2)
 end
 drawing.stroke("transparent")
 drawing.fill("black")
 drawing.text(4, 16, "Iteration #{iter}, Range +/- #{range}")

 img = Magick::Image.new(width, height,
Magick::HatchFill.new('white', 'lightcyan2'))
 drawing.draw(img)
 img.write("line_img_#{'%03d' % iter}.gif")
 anim_list << img.copy
end

def print_line(iter, line, range)
 puts "iteration #{iter} (range=#{range}): #{line.inspect}"
end

def perform_iterations(line, iterations, range, roughness)
 1.upto(iterations) do |i|
   line = displace_line(line, range)
   yield(i, line, range)
   range *= 2 ** (0 - roughness)
 end
end

anim = Magick::ImageList.new

# TODO: parse command line for options
width = 512
height = 512
roughness = 1.0

# set iterations to be enough to get "full resolution" for image but no higher
iterations = (Math.log(width) / Math.log(2)).to_i

perform_iterations([0.0, 0.0], iterations, 0.5, roughness){|iter, line, range|
 draw_line(iter, line, range, width, height, anim)
 print_line(iter, line, range)
}

anim.delay = 100
anim.cur_image.delay = 300
anim.iterations = 0
anim.write("line_anim.gif")