[sldev] [IDEA] MD instead of IK (was: Body motion and facial expression tracking, Microsoft did it)

[Boroondas Gupte]

Jan Ciger schrieb:
> Try to stand upright and then start leaning forward. At some
> point you have to either make a step or extend your leg backwards to
> stop falling over. That is what the solver was doing. It brings added
> realism to the animations and rules out poses that could reach the goal,
> but are not realistic for a normal human (standing on tiptoes at a 45
> degree angle, for example).
Wouldn't a static center of mass analysis rule out solutions that just
aren't possible in statics, but are very well possible as part of a
dynamic movement where inertia comes into play? Also, a lot of today's
canned animations are purposely displaying unphysical behavior to
achieve special effects (magic, slow motion, flying/hovering) or just to
be funny. Some of them might profit from the proposed retargeting, but
would be destroyed if the solver would only allow for physically
possible solutions.
>
> > I think adding the ability to do *simple* tweaks to existing animations
> > such as aligning avatars for a handshake might be helpful feature.
>
> Yep, but you do not need IK for that. And IK will still not help you
> with vastly different skeleton sizes - i.e. if my arm is too short, IK
> cannot make it "longer" to reach you. Not to mention that there seems to
> be the impression that "making tweaks to existing animations" is somehow
> "simpler". It is not - you only load the solver with more constraints.
Maybe I'm being naive here ... but if the problem is underconstrained,
isn't more constraints what you need so reduce the number of solutions?
(As long as the constraints don't contradict each other, that is.)

Though, to get the magnets-in-jello effect Argent was talking about, MD
with bond constraints and proper damping might do the trick cheaper
(both, implementation and performance wise) than real IK does. Combining
it with canned animations shouldn't be too difficult, either. The force
fields could probably even be chosen such that limbs are very unlikely
to penetrate the body.

cheers
Boroondas