Quick tool for CSS Refactoring - diffs screenshots against a reference

screenshot-diff.rb

require 'capybara'
require 'capybara/dsl'
require 'capybara/poltergeist'
require 'chunky_png'
require 'tempfile'  

Capybara.run_server = false
Capybara.default_driver = :poltergeist
Capybara.javascript_driver = :poltergeist

class Screenshot < Struct.new(:reference_file,:host,:path)
  include Capybara::DSL

  SUCCESS, FAILURE = 0,1

  def screenshot
    @screenshot ||= begin
      Capybara.app_host = self.host
      visit(self.path);
      image_name = '/tmp/ss.png'
      page.driver.render(image_name,:full => true)
      image_name
    end
  end

  def checksum_match?(file1, file2)
    ref_md5 = `md5 #{file1}`
    new_md5 = `md5 #{file2}`
    ref_md5 == new_md5
  end

  def reference_image
    @reference_image ||= ChunkyPNG::Image.from_file(self.reference_file)
  end

  def new_image
    @new_image ||= ChunkyPNG::Image.from_file(screenshot)
  end

  def highlight_diffs(new_image,diff)
     x, y = diff.map{ |xy| xy[0] }, diff.map{ |xy| xy[1] }

     new_image.rect(x.min, y.min, x.max, y.max, ChunkyPNG::Color.rgb(255,0,0))
     diff_path = '/tmp/diff.png'
     new_image.save(diff_path)
     `open #{diff_path}`
  end

  def compare
     
     return SUCCESS if checksum_match?(self.reference_file,screenshot)

     diff = []

     reference_image.height.times do |y|
       reference_image.row(y).each_with_index do |pixel, x|
          diff << [x,y] unless pixel == new_image[x,y]
       end
     end
 
     return SUCCESS if diff.length == 0
     
     highlight_diffs(new_image,diff)
     
     return FAILURE
  end

end

exit Screenshot.new('reference.png','http://localhost:9393','/report/aOM5U7').compare