[ODE] Increasing number of particales changes physics

[Megan Fox]

This may be obtuse, but I'm curious about something... joint
contraints work by removing axis of freedom from a given object,
constraining them to a particular orientation or region.  As I
understand it, the more constraints, the faster the joint and less
amount of impact on the sim speed.

Given that, would it be possible to make a "point" contact joint that
acted to correct the position of the body in question, but with fewer
axis of freedom (eg. no rotation), thereby acting faster than a
traditional contact joint?


Seemingly, you'd use the same collider either way (unless the collider
is doing something odd a sphere and a point collision should be doing
the same thing - which is to say, not much really, radius + center
point), but this would be the difference between a point and a sphere?

On 8/12/06, Roland Kindermann <iyo at gmx.de> wrote:
> Hi,
> I work with particles too. I think it would be nice to have a Point
> Geometry (which only consists of one point) for particles. It would
> probably be faster than a small Sphere.
> Cheers,
> Roland Kindermann
>
> Jacob Ole Juul Kolding schrieb:
> > OK I have a fixed step time and that works fine.
> >
> > The next problem is when I enable collision (So that the particles
> > bounce against a floor). When the simulation has up to 350 particles it
> > seem to run smoothly and stable, but above 350 it will eventually suffer
> > a slowdown death causing the app to be unresponsive.
> >
> > I switched to HashSpace and set the category/collide bits so that the
> > particles should not collide with each other but only the floor.
> >
> > Is this a bottleneck?
> >
> > /Jacob Kolding
> >
> >
> > On 8/11/06, *Jon Watte* <hplus at mindcontrol.org
> > <mailto:hplus at mindcontrol.org>> wrote:
> >
> >     Correct. You need to use a fixed time step. Such as in
> >     http://www.mindcontrol.org/~hplus/graphics/game_loop.html
> >     <http://www.mindcontrol.org/%7Ehplus/graphics/game_loop.html>
> >
> >     Jacob Ole Juul Kolding wrote:
> >     >  I'm implementing a particle system in ODE and have encountered the
> >     >  problem that when the number of particles increase the physics change
> >     >  in the the way the even though the same force is applied, the more
> >     >  particles are in the simulation the longer they will travel.
> >     >
> >     >  My guess is that since i step the world each frame, when the frame
> >     >  rate drops the step time increase which changes the outcome of the
> >     >  simulation?
> >     >
> >     >  Anyone have an idea how to help this problem?
> >     >
> >     >  /Jacob Kolding
> >     >
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-- 
-Megan Fox
Idyllon, LLC
http://shalinor.circustent.us/megan/resume/