[slscripters] PRIM_POS_LOCAL and prim drift

[Stickman]

Would this cause a child prim to drift away from its original position?

-----
while (TRUE) {
// Worded for readability
list l = llGetLinkPrimitiveParams(2,[PRIM_POS_LOCAL])
vector v = llList2Vector(l,0);
llSetLinkPrimitiveParams(2, [PRIM_POS_LOCAL, v]);
}
---

There's a long explanation around it... but I realize this is the core
of the issue.

If no one knows, I can set up a test to try to find out.

Thanks!

Stickman
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[Fred Beckhusen]

The wiki says for LlSetLinkPrimitiveParams that "Values may drift,
become truncated or be range limited. Some limits are applied by the
client during deserialization before rendering, others are applied by
the simulator before storing the values."

So I would say you can count on it happening.

I always thought that prims could drift, but the only proof i had was a
collection of things named "Object" at <0,0,0> in my sim. And I
heard that the Lindens had denied that it could happen.

But Tateru Nino did publish a picture of "prim drift" in actual motion
on a prim named "Bob", way back in 2007, which is just too good to not
post a link here.

Tateru has the final word on this subject at this link:

http://w__fbc__ww.secondlifeinsider.com/category/comics/

Enjoy Second Life:

Ferd Frederix

[AnnMarieSLFBI]

It is entirely possible.
Working from memory, in the days when you calculated local position from
global, especially if the object was in motion, you could accumulate
errors. I assumed it was due to changes in global position between
getting root and prim locations. If PRIM_POS_LOCAL is using the same
technique it is possible. My vehicle morphing program has to store the
original list of parameters to avoid cumulative errors on restoration.

Ann-Mare
from her laptop while she rebuilds her computer.

[Eloise Pasteur]

You can see it fairly easily if you set up a door and simply slide/rotate it by a fixed amount (and back) to open and close. It doesn't take a lot of movements for it to drift noticeably. Non-moving (theoretically) prims do it slower - but at least once a week they get saved and rerezzed with the sim gets updated and that will do the same thing. I have a windmill I built some years ago now. I don't use that area very often, went over and the floor was about 0.75m away from the walls thanks to prim drift.

El.

http://educationaldesigns.eloisepasteur.net/
http://eloisepasteur.net/blog/