Middlemanのimage_tagの拡張。srcsetでRetina用の画像を追加。

helper.rb

helpers do
  def image_tag(path,params = {})
    if !params.key?(:srcset)


      basename = File.basename(path, '.*')
      ext = File.extname(path)

      real_path = path.sub(basename + ext,basename + "@2x" + ext )
      real_path = File.join(images_dir, real_path) unless real_path.start_with?('/')
      full_path = File.join(source_dir, real_path)

      if File.exist?(full_path)
        params[:srcset] = image_path(real_path) + " 2x"
      end

    end

    super(path,params)
  end
end

any chance you could explain how to use this a bit more? Looks like an interesting way to use srcset