# File lib/rubygame/clock.rb, line 109
                        def tick()
                                now = Rubygame::Time.get_ticks() # ms since init'd Rubygame
                                @passed = now - @last_tick # how long since the last tick?
                                @last_tick = now # update last tick time
                                @ticks += 1         # increment ticks
                                @raw_passed = @passed # save unadjusted @passed

                                # Now we manually delay if we are too early, so the 
                                # frames per second stays approx. at the desired rate.
                                if @desired_fps and (self.fps() > @desired_fps)
                                        goal_delay = (1000.0/@desired_fps) - @passed
                                        unless goal_delay < 0 # which would mean we're too slow
                                                actual_delay = Rubygame::Time.delay(goal_delay)
                                                @passed += actual_delay   # why @raw_passed is different
                                        # else we are running too slow anyway, can't un-delay
                                        end
                                end
                                return @passed
                        end