[sldev] Body motion and facial expression tracking, Microsoft did it

[Dahlia Trimble]

I dont think the math or the complexity of IK is beyond all of the scripters
in SL, There are some talented scripters around who could easily solve the
problem, some of them in SL may even be PhD level mathematicians ;) Rather I
think synchronization and lag would prevent a lot of real time on-the-fly
animations. Currently animations are pre-recorded and many are cached. There
is a quite noticeable delay when new animations are signaled by the sim
before the clients play them, due to the need for the viewer to request and
download the asset. The assets are highly compressed and may only be a few
kbytes for any animation sequence.
I don't think that computing IK on the fly is all that expensive either, it
may only be a few hundred floating point operations per keyframe for each
skeleton, certainly not expensive for modern day hardware.

I *do* think that if real time on-the-fly animations were to be implemented
in any kind of believable sense, there would need to be an improvement made
in the speed in which the data could be distributed between clients. Somehow
I don't see it as possible with the current load that many SL sims have to
deal with already.

On Sat, Jun 6, 2009 at 3:44 PM, Jan Ciger <jan.ciger at gmail.com> wrote:

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> Argent Stonecutter wrote:
> > I don't think it would be anywhere near so hard as getting a reliable
> > animation overrider to work in the first place. :)
> >
> > Have you looked at the source for Franimation/ZHAO? Oh, there's a
> > certain amount of gratuitous yak-shaving in the code, but there's all
> > KINDS of special cases... and even then I'm always tinkering with my
> > copy to try and stop things like the skipping-up-steps effect.
>
> You are missing a crucial difference - an AO merely plays "pre-cooked"
> animations, turning off one and turning on another one. That is the
> trivial part. The script only triggers them. The special cases are due
> to the fact that an AO is a gross hack working around the fact that
> there is no way to tell SL to play different animations instead of the
> default ones.
>
> Generating a procedural animation, be it IK, simple reaching anim or
> walkcycle is several orders of magnitude more difficult - you have to
> actually control the whole thing and calculate positions/orientations of
> every joint and blend it properly. And you are likely doing this on the
> server, because otherwise you wouldn't be able to synchronize two avatars.
>
> Of course, from the script's point of view, it would be all black box.
> However, tweaking the inputs, e.g. for IK, is far from trivial,
> requiring deep understanding of how the skeleton works and the math
> behind. How many scripters actually understand the concept behind the
> rotation type (quaternion) and hierarchical transformations that are the
> basic element of this? Here you will be giving the scripters another
> black magic tool like that, probably even more complex. I doubt that
> many people would be capable of using it effectively.
>
> Regards,
>
> Jan
>
>
>
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