simple command line utility to create diff image of two URL.

webdiff.rb

#!/usr/bin/env ruby

# usage in the real life: 
#  when you want to compare changes between your development version and a production version :
#  webdiff http://sharypic.com http://sharypic-dev.com:3000
# 
# into the wild:
#  create a 'test suite' of your full website :-) [i'll parse my sitemap.xml]

require 'fileutils'
require 'chunky_png'

puts "usage: webdiff production_website dev_website" and return 0 if ARGV.size != 2

# desc:                 get two url then snapshot them in order to return a path to a diff image
# url_to_snapshot_a:    valid URL to website_a
# url_to_snapshot_b:    valid URL to website_a'
# return                a path to a diff image of website_a/website_a'
def process(url_to_snapshot_a, url_to_snapshot_b)
  path_to_snapshots = [url_to_snapshot_a, url_to_snapshot_b].map{ |url| snapshot url }

  create_image_diff(*path_to_snapshots)
end

def show_diff_image(path_to_image)
  %x[open #{path_to_image}]
end

# desc:                 take snapshot of the given url and return the path of the generated .PNG file
#                       under the hood, using webkit2png. see: http://www.paulhammond.org/webkit2png
#                       aliased: ln -s your_web2png.py /usr/bin/web2png
#
# url:                  accessible URL
# return:               path to snapshoted URL png file
def snapshot url
  basename = url.gsub /[^a-zA-Z0-9]/, ""
  webkit_to_png_convention = "-full.png"

  %x[webkit2png -o #{basename} #{url}]

  "#{basename}#{webkit_to_png_convention}"
end

# desc:                 compare differences between two images,
# path_to_img_a:        path to reference image
# path_to_img_b:        path to potentialy updated image
# return:               path to a newly created file highlighting area difference
# credits:              go to http://jeffkreeftmeijer.com/2011/comparing-images-and-creating-image-diffs
def create_image_diff(path_to_img_a, path_to_img_b)
  images = [path_to_img_a, path_to_img_b].map{ |path_to_img| ChunkyPNG::Image.from_file(path_to_img) }
  diff = []

  images.first.height.times do |y|
    images.first.row(y).each_with_index do |pixel, x|
      diff << [x,y] unless pixel == images.last[x,y]
    end
  end
  x, y = diff.map{ |xy| xy[0] }, diff.map{ |xy| xy[1] }

  images.last.rect(x.min, y.min, x.max, y.max, ChunkyPNG::Color.rgb(0,255,0))
  images.last.save('diff.png')
  'diff.png'
end

show_diff_image process(*ARGV)
return 1