[ODE] Simulations running in real time?

[Chris Royce]

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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