    # File lib/prawn/graphics/transparency.rb, line 14
          def transparent(opacity, stroke_opacity=opacity, &block)
            min_version(1.4)

            key = "#{opacity}_#{stroke_opacity}"

            if opacity_dictionary_registry[key]
              opacity_dictionary =  opacity_dictionary_registry[key][:obj]
              opacity_dictionary_name =  opacity_dictionary_registry[key][:name]
            else
              opacity_dictionary = ref!(:Type => :ExtGState,
                                        :CA   => stroke_opacity,
                                        :ca   => opacity
                                        )

              opacity_dictionary_name = "Tr#{next_opacity_dictionary_id}"
              opacity_dictionary_registry[key] = { :name => opacity_dictionary_name,
                                                   :obj  => opacity_dictionary }
            end

            page_ext_gstates.merge!(opacity_dictionary_name => opacity_dictionary)

            # push a new graphics context onto the graphics context stack
            add_content "q"
            add_content "/#{opacity_dictionary_name} gs"

            yield if block_given?

            add_content "Q"
          end