[ODE] ODE used in nesnausk's 3D demo

[Aras Pranckevicius]

> What did you need to optimize heavily?  It looks as if the parts of
> the wall never self-collide, and piles never seem to be more than 100
> or so boxes (assuming those are indeed box-shapes, they move as if
> they are), so where was the tweaking necessary?

At the whole-wall fracture scene there's some 1800 pieces (boxes)
falling out. That was "a bit" too much, so:

* First partition them into multiple colliding classes so that not
everything collides with everything, but each piece collides with 1/8
of all pieces. This is obviously fake, but oh well :)

* Make auto-disable tresholds pretty high, solver (quickstep)
iterations low, small number of contacts. Remove each body/geom from
world/space as soon as they're disabled (that's also fake, but
processing lots of disabled bodies also takes time).

* After that it was manageable, but in the end we spawned not all
>1500 pieces, but start spawning each 2nd or each 3rd when the total
body count is high, hoping that noone will notice. In the end it's
something like 500 pieces at the same time.

Nothing rocket science of course: some cheating and some tuning of the
parameters (the tuning takes time though).

-- 
Aras 'NeARAZ' Pranckevicius
http://nesnausk.org/nearaz | http://nearaz.blogspot.com