Megaprims - simple question.

I've just acquired a job lot of free magaprims, which I hope to use to replace multiple prims on some of my structures, to reduce prim count. These megaprims texture and link fine, so I'm wondering if there is any downside to using them. The invisible 'dimensional boundary boxes' of some of these megaprims are huge - does it matter if these invisble bits overlap neighbouring land? Also, are magaprims unstable? I've also heard they somehow cause lag.

It is possible to use mega prims sensibly, if you are VERY careful. My advice (and preference) is for them not to be used, if there were no issues, they would come as standard in the Library. The issues are broadly:

1. Overlapping prims into other people's land is intensely annoying
2. Overlapping across sim boundaries causes untold amounts of lag and can cause sims to crash
3. Anything that touches or physcially interacts with a mega prim causes a huge amount of lag (called a collision - and it eats up a LOT of sim resources)

Basically bad news all round. A simple way to look at it is that you do not get something for nothing, and mega prim users usually take that something from someone else.

That said, if you use them for walls that are made phantom (hence no collisions) you can just about use them safely. But you do this at your own risk, as LL might decide to pull them (this was subject to a discussion in the forums/blog a few weeks ago).

Never ever use a physical mega prim for a floor, every avatar walking on that floor will cause a huge amount of lag.

RO

I wouldent use mega prims at all concerning the current talk about them <torley linden office hours>, aparently one of the plans may be to remove mega prims and increase normal building size to 20x20x20 instead of 10x10x10, read the blog about it.

When your neighbor has mega prims hanging over your land, it can be quite annoying and very unfriendly. I would ask you to reconsider that since you obviously know there may or may not be an issue with them.

I'd follow Ee's link, and pay special attention to page 3, posts ~30-43... then make up your own mind...

not noted in that thread, but a moving cut mega (really any prim) can cause the floating up issue. megas should stay still, preferably not overhang neighbors (to prevent any chance of snapback effects seen in smaller prims), and never be physics enabled (which is NOT the same as being phantom)

OK, at the moment I've got one 40x20 mega in use as a sky platform floor at 600m. I'll go back later and put it back to 8 10x10s!

I am currently using some megaprims in a skybox at 671m. Does this cause more lag with how I'm using them, or does it really do anything?

I have a sculpted 40x40x40 mountain as the base for the Sky Isle, with a 40x40x40 full alpha non-phantom mega surrounding it, which acts as the floor. (I have it covered in 10x10x.5 sculpted prims, but standing on those looks bad, so made a floor below it from the mega) I also have 16 20x20x.5 prims in total surrounding the Sky Isle as boundaries so people don't fall off.

If what I'm doing will be causing immense lag for anyone, please tell me! Never really thought about it, as it doesn't cross sim boundaries, no physical prims at all, and they don't do anything besides sit there.

I can easily change it all to use normal 10x10 prims if what I'm doing is causing lag o.o

Lag seems to be relative based on the client, it seems. Avaria Kro is loaded to the rim with sculpted megaprims that make up our caverns, yet the sim FPS and my client FPS are both hardly affected at all, only the one or two scripted ones with texture anims (flowing water + sculpty) actually impact the simulator at all, and it's well below concern-raising limits (Less than 0.01 script execution time, conisdering there are only about 10 of those prims total in the sim, though if it was not megaprims, there would be probably 60 or so instead.)

My thought is that you're okay to use them as long as the bounding boxes (not the shapes themselves, but the entire bounding area around them) don't protrude outside your land.

It's not the visible prim that's overlapping. Just the bounding box, which is invisible to everything except minimap. You can pathcut a megaprim to a fraction of its size, but the fullsize still appears on the minimap.

Some of the overlapping/performance related issues above I struggle to corroborate.

Given a Linden's comments on megaprims in this very forum last month, it seems highly unlikely that megaprims will ever go away.

No. Recently a Linden said that prims larger than 512m caused lag in certain situations. Unfortunately a game of Chinese whispers ensued and now half the users of Second Life think mega prims positioned higher than 512m cause lag.

Higher != Larger

Okies.. I did remember reading that but didn't really think anything of it lol... I simply meant my use of megas in general ^^

Im only using them because I'm trying to have a Home, shop, and public skybox on one lot (around 10km) with only a little over 2k prims... so those extra 15 prims could end up hurting lol...

Thanks ^^

If it's perfectly still and completely contained within the boundaries of your own parcel, why not leave it where it is?

I've just completed an entire build which makes use of about six mega-prims between 20 & 50 metres, most of them path cut. This is at ground level, my parcel is surrounded on three sides and there are no issues with them. The sim performs very well indeed. Well it did until three dozen rotating "for sale" skyscrapers arrived this week anyways.

You're welcome. When used wisely, they are amazing prim-savers, and actually quite difficult to detect. =)

lol without me telling them people don't know I have an invisible prim as the floor... they think somehow I made the sculpties so you can walk ankle deep in the snow where it's higher and barely in it where it's shallow XD Like I made a true prim sculpty or something lol...

Okies so should be safe then..thanks again ^^

I forgot to mention originally that I got these megaprims from an automated display / vendor unit at New Citizens' Plaza, so I assume that they've been kosherfied by LL.

I'm not sure this is quite true. I think I've seen megaprims that are aligned to the axes and cubical (so that even the axis-aligned bounding box should be the same as the visual and the collision behaviour) appear bigger on the minimap.

As far as I know NCI is not an official Linden sanctioned group. I'm pretty sure that megaprims are not officially supported, but exist as a tolerated bug/feature.

anyway, I decommissioned the megaprim and replaced it with eight 10 x 10s, mainly as I had problems getting things to rez on top of it.

Conifer, the rezzing problems on top of megaprims in some situations are happening only in the Windlight client - I've created the JIRA issue about that a while back, please vote for it if you wish it fixed:
http://jira.secondlife.com/browse/VWR-3190

The problems with rezzing items on Megaprims has been around since way before windlight.

and as megaprims are a tolerated bug, I doubt the lindens are interested in fixing it.

This was a classic misunderstanding. The Z vector of megaprim placement is indeed irrelevant for lag.

However, I noticed, though, that megaprims near a region border cause more lag then within the region.

My private residence is located on an openspace sim, hence I need to be extra careful with anything adding to lag. One of my builds is a sky house which uses 32x32 megaprims for floor and ceiling. Placing this structure at (128, 12 works perfectly well. If I shift it to, say, (16, 16), noticeable lag develops instantly.

Maybe, but this specific bug is Windlight-related. Happens consistently in Windlight client as compared to official client.

As for Linden support... I'm sure they'll eventually decide something regarding megaprims, and I doubt that they will delete all of them since they are so widely used. Besides, if enough people vote for the issue, they might take a look at it, especially since it might not affect only megaprims, but other cut shapes as well.

The biggest problem I have with megaprims (besides a skyful of huge, ugly structures) is they make camera movement whacky. If you alt-zoom a regular prim to move the camera, then alt-zoom the megaprim next to it, the camera suddenly acts differently.

My workshop is make of 50x50s and I have this rezzing problem. The solution is to put an overlapping normal-prim surface, temporarily or permanently, where you want to rez objects. Rez objects on your "rug" (or whatever you made it look like) and then move them into place.