From: Joel VanderWerf <vjoel@...>
Date: 2005-11-12T12:23:39+09:00
Subject: Re: Accurate Timing in ruby

Daniel Sheppard wrote:
> You shouldn't time your game in terms of seconds - time it in terms of
> "game time" - give it a target FPS, but let it go slower.
> 
> Each 'game logic' turn should measure the start and end time, subtract
> the execution time from the target FPS and then sleep for the period of
> time to make up the difference. Instead of extrapolating the FPS from
> the time of the current frame, just keep a running count of frames, and
> reset the count once you've entered the next second.

Here's a pretty mundane implememtation of that idea, which has been
useful to me in some quasi-real time work. Hope it helps somebody.

http://redshift.sourceforge.net/timer/timer.rb

On a 1.7GHz Pentium, running linux 2.6.10, the timer can keep fairly
good time with a period of 50 microseconds, as long as you aren't doing
much else. It starts slipping as you get close to 10 microsec (running
as nice -n -20). I guess that gives a rough estimate of the overhead.

require 'timer'

count = 0
period_usec = 50.0 # microsec
period = period_usec / 1_000_000
duration = 10.0

Timer.every period, duration do
  count += 1
end

p count
p duration/period

-- 
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407