[ODE] Geometry passing through / timestep size

[Clay Larabie]

"I do it because my body moves fast, has few collisions and passing through
geometry
is not acceptable (pod-racer type game). "

So have you already implemented this method of ensuring objects don't pass
through? If so, can you share it?

Clay


----- Original Message -----
From: "Chris Campbell" <chris.campbell@l8tech.com>
To: <ode@q12.org>
Sent: Thursday, August 01, 2002 9:44 PM
Subject: RE: [ODE] Geometry passing through / timestep size


>
> The thing with how ode responds to collision is that you need to have
> geometries embedded in each other to find a penetration distance. If an
> object passes right through another, but is not embedded at the
before/after
> timesteps, there is no penetration etc.
> My suggestion to fix... well... hack this would be:
>
> Keep track of the last position the body was at.
> After each timestep, use the lastPos-to-currentPos to check if there was a
> collision (not penetration!).
> If so {
>       Move the body back to the earliest collision point.
>       Make up a contact joint for it, hardcode penetration to a very small
> value.
> }
>
> This may mean you have to write some of your own collision routines, but
it
> will cure the passing through problem nicely. Since you only need one
> contact for the body (the earliest collision), it's a bit less load on
ode's
> solver.
> There are drawbacks of course. It's a bitch to find that earliest
collision
> point for anything other than a sphere. Since you always set penetration
to
> non-zero, bodies will slide slowly down slopes even when the friction
should
> be keeping them still. Finding the right collision point for moving bodies
> which collide during a timestep is... non-trivial.
> Anyway the point is that doing this is not suitable all the time. I do it
> because my body moves fast, has few collisions and passing through
geometry
> is not acceptable (pod-racer type game). However where it is reasonable to
> place a hard limit on how far a body can move per timestep (walking human)
> ode's standard penetration-from-embedded-state is of course best.
> Hmm... I still haven't decided how to mix these though, say if pod-racer
> collides with human... ouch :)
>
> > -----Original Message-----
> > From: Clay Larabie [mailto:c-larabie@rogers.com]
> > Sent: Friday, August 02, 2002 1:38 PM
> > To: Erwin de Vries; ode@q12.org
> > Subject: Re: [ODE] Geometry passing through TriList
> >
> >
> > What are your suggestions if I wanted to fix this?
> >
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