[ODE] Non-deterministic behavior (tri-mesh Collisions?)

[Shaul Kedem]

Josh, You are welcome,
 Two ideas: 
  - First, check the posts about floating point
problems, it might help.
  - Second, try moving the callback function into the
trimesh tests (there are two of those) - it might give
you some insight over whether this is reproducable
with ODE drawstuff/tests.

 About the tri-mesh collision, this is a bit of a
black hole to me, so I can't really suggest anything.

Hope that helps,
Shaul

--- Josh Welber <josh@largeanimal.com> wrote:
> Shaul--
> thanks for the quick reply -- I was hoping to hear
> this (that it is a bug 
> in our code, not ODE). In any event, to answer your
> questions:
> 
> -we have tested on XP and win2K same behavior on
> both
> -we are not using directX (although we might).  We
> have integrated ODE into 
> the Torque engine and that are using its OpenGL
> version (it can do either 
> DX 8 or openGL, but the OpenGL support seems better)
> -the non-deterministic result seems to come as the
> result of a collision 
> between the ground (a trimesh) and a sphere (or
> maybe any object, not sure).
> -no random numbers.
> 
> My suspicion is that something about either the way
> the contact joints are 
> created by us (in the callback function for those)
> or the way the 
> collisions are detected inside ODE is causing this. 
> I know that the 
> initial state each time is the same.
> 
> So, if you have any thoughts on how one might,
> inadvertently and 
> non-obvoiusly, create non-deterministic behavior
> when creating contacts 
> from collision information would be good to hear it.
> 
> -josh
> 
> At 08:41 AM 8/24/2003 -0700, you wrote:
> >A long long time ago, ( in a galaxy far far away? )
> >there was a long discussion on stuff like this in
> the
> >context of floating point arithmetic and how to
> save
> >floating points to a file/load it from it.
> >
> >I don't know if that is your problem, but you
> should
> >check it out.
> >
> >Apart from that: are you using some random number
> >anywhere in there? is it non deterministic on all
> of
> >your computers/OSs?
> >Do you use directX ? there is something with
> floating
> >point resolution in there as well.
> >
> >I asked if ODE is deterministic once (regarding the
> >faststep, thinking that the regular solver is
> >deterministic.. and by my tests it is) and got an
> >explicit answer that it is.
> >
> >So, to summarize: it's probably a bug in your code
> :-|
> >
> >Shaul
> >
> >
> >--- Josh Welber <josh@largeanimal.com> wrote:
> > > Does anyone have experience with ODE giving
> > > non-deterministic
> > > results?  What I mean is specifically this:  We
> have
> > > a simulation where you
> > > shoot a ball out over a terrain and it starts
> > > rolling from there.  The only
> > > user input is the direction/spin/force that the
> ball
> > > is launched with --
> > > and all these are set with discrete controls.
> The
> > > collisions in this case
> > > are all between spheres and triMesh.  We have
> found
> > > that the ball does not
> > > in a deterministic manner -- but rather bounces
> > > oddly sometimes, sometimes
> > > acts as expected.  This is sometimes worse if
> there
> > > is friction in the
> > > collision contact, but even for frictionless
> > > collisions it still reacts in
> > > a non-deterministic way.  Does anyone have any
> ideas
> > > about this one, seen
> > > this behavior themselves?  I saw the posting
> > > regarding friction causing
> > > unexpected results -- this is a different
> problem.
> > >
> > > thanks
> > >
> > >
> > >
> > > Josh Welber
> > > partner/tech wrangler
> > > Large Animal Games
> > > http://www.largeanimal.com
> > > t: 212.989.4312
> > > f: 305.489.5790
> > >
> > >
> > > _______________________________________________
> > > ODE mailing list
> > > ODE@q12.org
> > > http://q12.org/mailman/listinfo/ode
> >
> >
> >__________________________________
> >Do you Yahoo!?
> >Yahoo! SiteBuilder - Free, easy-to-use web site
> design software
> >http://sitebuilder.yahoo.com
> 
> Josh Welber
> partner/tech wrangler
> Large Animal Games
> http://www.largeanimal.com
> t: 212.989.4312
> f: 305.489.5790
> 
> 


__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free, easy-to-use web site design software
http://sitebuilder.yahoo.com