[ODE] one way collision

[David Walters]

> I have two types of object that I want to collide. I only want one of
> the objects to bounce of and the other other object to continue like
> before, without contact joints being created and changing its
> simulation.
>
> We are using it to create some client side particle effects and want
> to keep the effects out of the deterministic part of our simulation.
>
> Any suggestions on how to achieve this?

Hi, yeah - if you create a contact joint between body_a and NULL
instead of body_a and body_b; then body_b will be unaffected by the
constraint and happily keep steamrollering along while body_a will fly
away or whatever.

In my engine I determine 'immovable' rigid bodies by an instance of a
class associated to the geom with 'dGeomSetData'. I ended up having a
moderately complicated structure here where the class I bind has
methods to determine specific response taken from Lua scripting - but
if you want a very simple solution just use 'dGeomSetData' with a
struct or even a bool :-)

I hope that covers everything, I'll elaborate if I've not made sense...

Regards,
David Walters

p.s. Toribash is great (despite me being terrible at it), well done
with that :-)