XSI7 dynamics oddity...

[r10k]

This is my second time posting this (first time seems to have been killed during the forum downtime).

After creating an XSI7 rigid body simulation (a simple torus falling on a plane) I found the simulation changed depending on whether I scrubbed the timeline, or played the animation. In one instance the torus would slide and fall off, while the other time it'd stay on the plane. Most of the time it'd stay on, but every now and then with the timeline control it'd slide off.

Does anyone know why this might happen? I get the feeling I've missed something, but the manual hasn't helped me figure it out.

[r10k]

No one knows? I guess this is a bug then.

[ThE_JacO]

Playing every frame ensures that the state before and current are consistant.
When you scrub, based on the speed you scrub at, frames might be dropped and the look-up of the state before might be inconsistant.
It's pretty normal behaviour for state based simulation.
Also this is a simulation/dynamics thread, so I'm moving it for you in the right section of the forum.

[r10k]

Thanks for moving the thread, ThE_JacO. It's hard to know where is best to post somedays.


It's pretty normal behaviour for state based simulation.


Okay, good explanation. I am left wondering though, why isn't this mentioned in the manual if it's so normal? The manual makes it sound as if both results should be the same.

[ThE_JacO]

Don't know, maybe G can answer that.
Also bear in mind that mine is a guess based on general knowledge of how dynamic systems work, it doesn't necessarily mean I'm right and it might be an issue.
IE: If you're in standard mode even scrubbing, if you scrub too far, should trigger a simulation of the frames you're "skipping".

I'm somewhat positive I'm guessing right, but like somebody said: "for every problem there's a solution that's simple, elegant, and wrong" :)

[r10k]

You're not talking about the G Man from HL2, are you? ;)

I'll keep experimenting and see if I can figure the thing out. No one else I've heard of has mentioned this kind of thing, but being a newb to dynamics in XSI (beyond Foundation, anyway) I guess anything is possible. If it is an issue though, I would have thought with all the version 7 testing that supposedly has gone on someone out there would have noticed by now. I mean, if it is a problem, it isn't a small one :)

[Ronald]

Scrubbing or playback should give you the same results. In both cases all frames in between will be simulated and in the end give you the same results.

If you could contact support@softimage.com with repro steps, that would be greatly appreciated.

Thanks,

- Ronald

[r10k]

Thanks Ronald, will do... as soon as I recreate the issue again. Stupidly I forgot to save my test scene. I'm pretty sure I can reproduce it again however, as it was a super-basic scene.

EDIT: Actually, I can't seem to... so please chalk this one up as one of those, "XSI is acting nuts again, so just restart it." I also ran into another one of those moments tonight when running a rigid body simulation- a model kept popping between the different modifier ops that'd been applied to it as the animation ran. One restart of XSI later, and the issue is resolved. I'm guessing freezing models is better for simulations anyway though, so I'll do that in the future.