[fluxus] advice about hijacking collision data

[Dave Griffiths]

> Thanks for the response.
> I am using the cvs and I did just look at that example.. nice.
> An id for collisions would be very nice, it would help me selectively
> exchange information between objects based on interactions.
> Do objects have have stored "center" point or is there any function in
> fluxus that will give the center point of a box, sphere, etc?.. I
> realize I could calculate this myself but i figure it would be useful
> for others as well, I'm basically wanting to calculate rough distances
> between objects.

the official way to find the position of an object is to do something like
this:

(grab obj)
(set ((position (vtransform (vector 0 0 0) (get-transform))))
(ungrab)
...
)

so we find the position of the object's origin (0,0,0) in world space. you
can move the origin of an object by (apply)ing a transform to it's points.

this should also work after submitting an object to ode

> One thing I noticed. Fluxus segfaults on my computer when i try to
> kick a passive box, i realize i shouldn't do this but a segfault isn't
> so nice :)

oops, I'll fix it, cheers. You could also hurt your foot behaving like
that... :)

> Do you think it would be possible to put active objects inside other
> objects?  So far it looks like you cannot with fluxus.  Like a sphere
> that has another sphere bouncing in it.

this is something I'm planning to look into. it might be the case that we
can specify negative volumes and ode will take care of it, it won't
currently do that if you specify a negative scale on an object, but its 
something I'll try. if that doesn't work then I'll look into supporting
tri meshes as collision volumes so we can model containing volumes
directly.

other than that, you can isolate space by positioning multiple ground planes.

> Also, I'm don't quite understand the surface-parms (I even read the
> ode docs a bit), can I set them to get perfectly elastic collisions?

I think so, you can make the collisions really quite unstable so they get
out of control, so there will be a sweet spot I imagine. I don't fully
understand the parameters either, other than the first two are to do with
friction and the last two are bounciness. it looks like there are some
extra ones that I need to feed through too.

> btw, is there an irc channel that people using fluxus hang out on?

I'm not a great irc user to be honest, although maybe we could sort out
some kind of remote fluxus workshop at some point if people are
interested.

the physics system is one of the least used of fluxus's features so bug
reports and feature requests are very welcome - although I can't promise
fast turn around at the moment :)

cheers,

dave