[ODE] Simulations running in real time?

[Megan Fox]

60hz (stepsize of 0.016) is the usually-cited recommendation, and
iters is just something I used in my own code for various debugging
and haven't bothered to remove yet.

-Megan Fox

On Tue, 29 Mar 2005 17:50:51 +0100, Chris Royce <croyce at ntlworld.com> wrote:
> Thanks so much for your reply, what is the iters value for? or is that just
> for debugging.
> 
> I pretty much follow the way your algorithm works,
> 
> so totalTime is only set as 0 when program is initially started, constantly
> varies depending on the speed of the application. What would you suggest as
> a good step size?
> 
> Thanks again Megan.
> 
> Chris
> 
> ----- Original Message -----
> From: "Megan Fox" <shalinor at gmail.com>
> To: "Chris Royce" <croyce at ntlworld.com>
> Cc: "ode" <ode at q12.org>
> Sent: Tuesday, March 29, 2005 5:44 PM
> Subject: Re: [ODE] Simulations running in real time?
> 
> > deltaTime is, as you deduced, the frame time, the time passed since
> > the last cycle.  totalTime is just a variable that starts off at 0 to
> > which I add the deltaTIme each frame, and from which I subtract the
> > time step until it is below the time step's size.
> >
> > I do this because it doesn't lose time this way.  Imagine if you had a
> > timestep of size 0.016, and then a delta time of 0.015 came up.
> > Consistently.
> >
> > You would want to carry that 0.015 to the next frame (because you
> > didn't have enough time to run a physics step yet), add the next delta
> > time, making your totalTime 0.03, and THEN run a physics step,
> > subtract your deltaTIme, and pass the remaining 0.014 total time into
> > the next cycle.
> >
> > If you don't do it this way (or a similar way), you lose time, and
> > your system fails to operate in real-time.
> >
> > -Megan Fox
> >
> >
> > On Tue, 29 Mar 2005 17:27:36 +0100, Chris Royce <croyce at ntlworld.com>
> > wrote:
> >> In this example what is totalTime and deltaTime.
> >>
> >> deltaTime is this the time taken for the simLoop method to be run ?
> >>
> >> totalTime is defined as what.
> >>
> >> Sorry im a little lost on which is which.
> >>
> >> Cheers
> >>
> >> Chris
> >>
> >> ----- Original Message -----
> >> From: "Megan Fox" <shalinor at gmail.com>
> >> To: "Hampus Soderstrom" <hampus at sxp.se>
> >> Cc: <ode at q12.org>
> >> Sent: Monday, March 28, 2005 6:25 PM
> >> Subject: Re: [ODE] Simulations running in real time?
> >>
> >> > Just use code something like this:
> >> >
> >> >    // Make sure time is accrued properly for the phys step count
> >> >    this->totalTime += deltaTime;
> >> >
> >> >    // Then advance the world up to present time
> >> >    unsigned int iters = 0;
> >> >    while(this->totalTime > PHYS_STEPSIZE)
> >> >    {
> >> >         // ... entity processing
> >> >
> >> >        nOpende::JointGroupEmpty(this->physContactJointGroupID);
> >> >        nOpende::SpaceCollide(this->physColSpaceID, this,
> >> > this->PhysCollisionCallback);
> >> >
> >> >        nOpende::WorldQuickStep(this->physWorldID, PHYS_STEPSIZE);
> >> >
> >> >        this->totalTime -= PHYS_STEPSIZE;
> >> >
> >> >        iters++;
> >> >    }
> >> >
> >> >
> >> > Very simple.  It runs ODE in real-time with a fixed timestep, without
> >> > loosing those fractions of a timestep you'll drop if you're just doing
> >> > "if deltatime > X"
> >> >
> >> > -Megan Fox
> >> >
> >> > On Mon, 28 Mar 2005 22:45:21 +0700, Hampus Soderstrom <hampus at sxp.se>
> >> > wrote:
> >> >> You could also lock he framerate to 60 pfs or something. On a computer
> >> >> that is too slow and can't keep up with the framerate you selected it
> >> >> will run slower though.
> >> >>
> >> >> 2005-03-28 kl. 20.28 skrev George Birbilis:
> >> >>
> >> >> > use multiple threads
> >> >> > see a paper at the Novodex website (now called Ageia or something),
> >> >> > search for Novodex SDK papers and at see the PDF about
> >> >> > multithreading.
> >> >> > You can apply similar technique to ODE I suppose
> >> >> >
> >> >> > -----
> >> >> > George Birbilis (birbilis at kagi.com)
> >> >> > Microsoft Most Valuable Professional
> >> >> > MVP J# for 2004 & 2005
> >> >> > http://www.kagi.com/birbilis
> >> >> > --------------
> >> >> > ----- Original Message ----- From: "Chris Royce"
> >> >> > <croyce at ntlworld.com>
> >> >> > To: "ode" <ode at q12.org>
> >> >> > Sent: Monday, March 28, 2005 4:10 PM
> >> >> > Subject: [ODE] Simulations running in real time?
> >> >> >
> >> >> >
> >> >> > Hello there I'm trying to get my simulation to run in real time,
> >> >> >
> >> >> > Basically the problem I'm having at the moment is that the
> >> >> > simulation
> >> >> > is running at different speeds on different computers. I'm working
> >> >> > in
> >> >> > C++ and using the drawStuff interface.
> >> >> >
> >> >> > I'm also noticing that by changing the dWorldStep value the motion
> >> >> > varies quite considerably, whereas I'd expected to run simply faster
> >> >> > or slower ?
> >> >> >
> >> >> > Thanks for any advice
> >> >> >
> >> >> > Chris
> >> >> >
> >> >> >
> >> >> > -----------------------------------------------------------------------
> >> >> > ---------
> >> >> >
> >> >> >
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