On-demand image sizing for Comfy and S3 using ActiveSupport::Concern. On-demand concept/code by: http://www.ryanalynporter.com/2012/06/07/resizing-thumbnails-on-demand-with-paperclip-and-rails/

gistfile1.txt

# ----------------
# file_concerns.rb
# ----------------

require 'uri'

module Models
  module ComfortableMexicanSofa
    module FileConcerns
      extend ActiveSupport::Concern

      def styles
        unless @dynamic_style_format.blank?
          { dynamic_style_format_symbol => @dynamic_style_format }
        else
          { :cms_thumb => '80x60#' }
        end
      end

      def dynamic_style_format_symbol
        URI.escape(@dynamic_style_format).to_sym
      end

      def url_by_format(format=:original)
        if(format.is_a?(Symbol))
          file.url(format)
        else
          @dynamic_style_format = format
          file.reprocess!(dynamic_style_format_symbol) unless file.exists?(dynamic_style_format_symbol)
          file.url(dynamic_style_format_symbol)
        end
      end

      included do
        #  override implementation to support on-demand styles/sizing
        has_attached_file :file, ::ComfortableMexicanSofa.config.upload_file_options.merge(
          :styles => Proc.new { |attachment| attachment.instance.styles }
        )
      end
    end
  end
end

# ---------------------------------------------------------------------
# an initializer file...to extend Comfy's file.rb with file_concerns.rb
# ---------------------------------------------------------------------

Cms::File.send(:include, Models::ComfortableMexicanSofa::FileConcerns)

# ----------------------
# some constant sizes...
# ----------------------

CMS_IMAGE_SIZES = {
  :banner => '1280x250#',
  :home => '1280x500#',
  :venue => '892x300#'
}

# -----------------------------------------------------------------------------
# now get a file and request the image URL (image will be created if necessary)
# -----------------------------------------------------------------------------

file.url_by_format(CMS_IMAGE_SIZES[:home])