    # File lib/prawn/font/ttf.rb, line 26
          def compute_width_of(string, options={})
            scale = (options[:size] || size) / 1000.0
            if options[:kerning]
              kern(string).inject(0) do |s,r|
                if r.is_a?(Numeric)
                  s - r
                else
                  r.inject(s) { |s2, u| s2 + character_width_by_code(u) }
                end
              end * scale
            else
              string.unpack("U*").inject(0) do |s,r|
                s + character_width_by_code(r)
              end * scale
            end
          end