Self-destructive Prims

One of my chief irritations these days are misaligning prims.

I built a castle at the new CritterLand sim. When I build... I take great effort and pride in building totally seamless. So it's with great irritation that I come back to my new castle to find gaping seam holes, slightly-misadjusted prims, edges no longer meeting, etc. (see the top line of the castle in the photo... super visible).

As bad as this seems, it pales in comparison with prims that get up and move off a sim by themselves... effectively deleteing themselves to your Lost and Found.

Computer graphics is basically MATH. You define the XYZ dimensions of a prim, its exact XYZ co-ordinate and XYZ rotation, and there it goes. There is no logical reason that I can think of that these things should ever change once they're set down. So why are builds tearing themselves apart?

From what I can see in that picture, you have a case of the traditional sparklies.

Traditionally seams (or sparklies) are caused by floating point error in the 3D.
All 3D engines use floating point maths for just about everything, now the problem with computer floating point maths is that it is inprecise, and errors creep in. This error is caused by the small problem that floating point numbers are infinate, and the computer has to round off a floating point number to a discreate value. This can open up seams where they cannot logically exist. Its not your fault, its not Linden Lifes fault, its a fundimental problem with the way a computer processes floating point maths.

A lot of modern computer games, even high end ones, suffer from seams, however seams are nearly invisible if the background behind them is a similar colour to the texture either side of the seam. So after the artists have ensured the edges of a polygon are mathematically true to each other, and the coders have done all they can to fix the edge algorithum. The background is then set to 'hide' the seam.

Also any antialasing thats in use tends to remove seams.


Anyway heres a link to an article explaining floating point math inprecision.
(see the first section "Rounding Error"
http://docs.sun.com/source/806-3568/ncg_goldberg.html


Justin.

Nope, this isn't sparklies, nor seam problems. This is a documented and well-known case of SL prims moving under their own volition. Sometimes this gets so bad that a prim will move itself off the edge of the sim-- effectively destroying that prim (it returns to your lost and found, but then you have to go to the trouble of trying to figure out where it came from and how to put it back exactly).

As a case in point: I made a perfectly seamless floor and LOCKED it in place. Next day I returned to find sections of the floor "lowered" by about 1/10 of a meter--more than just a seam-- a gaping ledge! Obviously, there is something in the system that is allowing/causing prim parameters to change without the direction of the creator.

This is a well-known bug that needs to be fumigated. ;D

You know... I've been building for over 2 years here. I build by the numbers, I'm a pretty precise prim doodler.

I've never seen these prim-drift problems. Ever.

It's been a constant complaint for as long as I've been here, but... I've never seen it.

I wonder why?

Maybe certain building techniques bring them out? Connection issues? Ninjas?

LF

This isn't a new issue. I brought up this subject quite a bit ago actually. Along with others. It's very irritating, and nothing can be done to fix it, that the Lindens are aware of. This is especially an apparent issue when building at high altitudes, when things break apart easily even while linked!

I'm with Lordfly on this one. While I've seen many bugs that can make building difficult come and go, I've never seen one that involved prims moving without outside help.

If I logged back on to see such an offset as described above (which I never have), I'd suspect lost packets while building as the culprit. If you are positioning something by hand, even with the grid, and a packet is lost that contains the new position of a prim, your screen won't update with that new position yet the server will.

If I'm draging a prim over to join a wall, with the grid on, and overshoot by one grid tick, BUT that last update packet is lost on it's way to me... Then the wall will look right to me, but be wrong on the server (if I didn't do ANYTHING to cause an update to be sent again). When I log in the next day I'll see it as wrong.

MY biggest beef when it comes to alignment is accidental dragging while moving around. If I have each level of a building linked together and I'm walking through it, if I click on something (like a wall) and hold the mouse button down a tad too long, the whole section of the building will MOVE. And me not even in EDIT mode! I SO HATE that.


Oh, and take a look at your castle close up too. LOD (level of detail) is reduced when you are farther from an object. This means it uses fewer verticies to build the prim which renders faster but slightly changes the shape. It is most obvious on curved shapes like spheres, cylinders, and tori.

[ Interesting Effect: Make two spheres the same size and of different colors. Give them each a script that puts a different TargetOmega spin on them, and put them in the exact same position. ]

Hi Way,
You aren't alone...building in Hartwick a couple of months ago, I nearly went mad with problems due to a build unlinking itself as soon as linked, and pieces of it moving without permission.

Eventually I took a copy, went to Natoma and experimented. When I linked the cottage in Natoma it stayed linked and stayed in position. Deleting and replacing the one in Hartwick with the one I had linked in Natoma made no difference - it unlinked and had prim rot too.

I have had about ten builds where I have had multiple problems with unlinking and moving, out of the 100s I have done. I think that using prims originated by more than person or in more than one group, can prompt it to happen, but apart from that I can't find anything which is common to all the builds I have had the problem with.

Currently in Rapture, I have had prim rot causing a non-phantom prim to be phantomised, and sinking prims on a high build. one of the floors has driven me to distraction...I have taken in out of the building, aligned using numbers, checked that it is OK with no gaps or visible joins, replaced it, and found that a gap has opened up with a dotted line effect. Initially it annoyed me - now I just colour the seams and ignore it .

I must admit that as SL and computer programming is all magic to me anyway, I have wondered what on earth causes the problem...I like to think that in a parallel universe, other people have phantom prims solidify and poorly built floors align themselves....
best wishes
Cali

Yeah, I understand. Dunno. It's like your car always messing up until you take it to a mechanic, then suddenly everything is just peachy...

Someone mentioned maybe it was a packet loss issue. While I'm sure that is the case in some instances... I'll tell a story. I was standing in ElvenGlen one day and a standard, everyday prim came waltzing by me under its own power, pretty as you please. Crossed right in front of me, moved off the sim. It was one of my prims, had been sitting in its locations for ages... and just decided to get up and move, walk off the sim, vanish into my lost and found. I have seen this happen at least 4 or 5 times, with my own eyes. I have numerous times, on various sims, suddenly had a prim report it had moved off sim and had returned to my lost and found... no earthly reason whatsoever.

I go to the sim, and sure enough, a chunk of a build is gone. The build had existed for weeks, was functional, and locked. So why do prims move on their own?

Who knows. But as several have commented... sure is irritating. I *hate* building a perfect, seamless build only to come back a week later and find gaps all over.

Prims up'ing and moving.

Well I don't know the code base, but if it almost sounds like a pointer has gone wonky in the Sim computer.

Its the ghost in the machine haunting us all

Here's an idea: once you position a prim have it run a script that stores its coordinates in the description string. Then have this script periodically compare the actual position against the stored position. I got the idea of using the description string as persistent prim state from someone in the forum.

It would be interesting to see if a prim gets moving_start() or changed() events when prim rot occurs.

I hit the same problem constantly, but especially when it comes to large object/buildings. I just finished building a high-rise apartment complex, and time and time again the pieces would spontaneously unlink. It drove me absolutely fracking nuts!

Eventually after much swearing and cursing I think I figured out at least part of the problem. Apparently within SL the rules used for linking are not only affected by the distance between prims, but also factors in prim size. What I was finding that the small prim I used as the root (a cylinder that was my 'position marker') was causing the unlink. If I resized the root prim to large (to match the rest of the object) the unlinking went away.

In addition, many times I'd position a piece by using the number entry boxes, the piece would not visually move, but the system would 'think', it was moved. The actual piece wouldn't reposition until I dragged it with an arrow or used the up/down buttons next to the entry box. Sometimes the only choice was to relog and double-check.

It was a hair-pulling experience, to say the least!


- Newfie

If your getting any packet loss during building it can cause prims to jump around all over the place. I take a brake during these periods and do something else till my connection improves.

I found that alt-click on the object to rotate the camera around it also makes the prim jump into place.

Have to admit curiosity that packet loss would cause this... unless of course, the packet loss is losing prim co-ordinates. That's possible... but doesn't explain prims getting up and moving on their own and vanishing back to lost & found. Like someone said.. math is wonky somewhere.

And now, over a year later, they fixed this in the 1.7 build and people are complaining about it.

I do lots of prim stuff (hell, I had a bug *named* after me because I'm that insane) but I've yet to see these problems. I guess either I build a lot procedurally like Tiger or Lordfly, or something else is going on here.

I vote ninjas.

for a long time I avoided prims moving by never linking them, or linking as little as possible.

But recently my school had a little "foundation move" where floors moved at least .5 meters.

Well, if you notice the date of this thread, this isn't a new complaint.

Also, are you sure it's fixed in 1.7?

You misunderstood me. What I mean is people are complaining about the fix!

AH! Drat written word! Can hear no inflections!

dunno if this is in any way related, but if you have the "edit linked" box checked, but are working on a non-linked object, the positional/rotational changes don't stick. might explain things "hopping back" when you're moving them around by typing in numbers. as far as drift goes, I've very new to SL, but I have exprienced it in a high traffic sandbox over a course of 3 hours. I was working on a very detailed avatar "head" and I noticed that the root prim had been rotated by .001 on the y axis for some bizzare reason. When editing in my "Home" sim (mostly empty with unsold property and very low lag), I haven't encountered any kind of drift/errors. I'm wondering if it might be a case of packet loss/corruption under high loads.

I've had completed items subject to prim drift in my inventory that were otherwise perfect before I put them there.

I havent been around as logn as LF but i also have pretty much no problems with prim drift or the sort. A few times a prim has moved itself to a former location (usualy when i have used edit linked parts) but i have learned not to do that, I have few issues with building that many seem to have.

LL must just like us LF

You've known me a long time, LordFly, and you know that even though I don't produce much now, I'm not exactly a crappy builder myself. Anyway, I have seen this in the past, but in a very specialised set of conditions... It happens if I build within 5m of the edge of a sim - on any of the x, y or z co-ordinates (for z, I mean very close to sim base 0... high (768 or up) is another issue. You can overcome the problem by pre-linking of course.

So yes, it can happen, and of course, if you're building by eye, it's going to happen more as the movement tools aren't exactly accurate.

Just my £0.02 (uk) worth.