[ODE] Particle/cloth/skeleton (was: Re: Choleski factorization)

[Antonio_Martini@scee.net]

> He would just run
>the key frame animations as usual then feed the current and
>old positions into the particle skeleton system then apply the
>bullet forceand the body would react correctly carrying the
>correct momentum that it got from the keyframe animations.
>That would be a bit harder to do using a normal velocity/force
>based approach.
as far i have been able to see in the game you can only shoot dead
bodies. But as i said i could have missed it.
talking about reactions to bullets or other external forces that would
come out automatically once you have a control method in place(inverse
dynamics based,
PD controllers,etc..)in a ODE stile simulator. Of course
having inverse dynamics in ODE would make it slower because it would be
O(n^3) unless we are able
to exploid some kind of sparsity, but as i said I use a optimised
Featherstone's and that's O(n) and
very fast. talking about rigid bodies modelled as particles a guy called
Bart Barenburg(im sure the spelling
is wrong) wrote a Phd about it a long time ago. May be there is something
useful in there but i cannot find
his paper anymore.






"Joakim Eriksson" <jme@snowcode.com>@q12.org on 24/03/2003 13:17:51

Sent by:    ode-admin@q12.org


To:    <ode@q12.org>
cc:
Subject:    RE:  [ODE] Particle/cloth/skeleton (was: Re: Choleski
       factorization)


> >This is not true. The constraint system was activated as quickly as
> >any force (Bomb/bullet) hit the character so there was some large
> >forces involved sometimes. I was at GDC and heard his talk (He's
> >a very funny and good speaker by the way) and there he showed a
> >level with a bunch of characters and then he set off a big bomb.
> >In the middle and they all flew away. Looked fun.
> i wasnt at GDC so my knoweldge is limited to what i have seen
> in the game.
> I havent fully played it but i havent noticed any explosions
> affecting the bodies.
> Probably i had a too superficial look at the game.

Can't say I have seen that many explosions in the game either
but that could be because when you blow up a bomb in the game
your usualy a long way from the blast at that point. (Car bombs
are a good example)
But something you will have seen a lot is how bodies react to bullets.
Thats one of the nice things with that system. He would just run
the key frame animations as usual then feed the current and
old positions into the particle skeleton system then apply the
bullet forceand the body would react correctly carrying the
correct momentum that it got from the keyframe animations.
That would be a bit harder to do using a normal velocity/force
based approach.

> >In the paper he states that he models rigidbodies using a
> tetrahedron.
> >Its hardly not used in the games and I realy dont know why.
> But in one
> >place I remember they had a trashcan that you could tip over and
> >shoot at. It was surprisingly fun =)
> yes but that's far from stacking etc...
> i dont remember the details of the paper but i think he described the
> way the method could be extended to generic rigid bodies without
> saying that they actually implemented a system like that.

Not sure I follow you. What he did in hitman was "generic" rigidbodies.
You can stack them all you want and do everything you can with
normal rigid bodies. I'm not sure how stable the stacking would
be but I seriously think it would be stable enough for most
(game) uses.

A constraint system built using that tetrahdron model is very stable.
I did a test about a year ago that involved 256 bodies and 512
body-body constraints and it ran at 20Hz on my P3 866.
However they all had the same mass and the only constraint modeled
was body-body. So there wasnt any collision constraints and those
are the hard to do in that system.

> >I have been searching for this paper but I cant seem to find it
> >anywhere. Do you known where I could get a hold of it?
> i emailed directly the author, in order to save him same time
> i will email it to you.

Thanks!

/Joakim E. - http://www.planestate.net

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