Downsides to Megaprims?

They seem too good to be true, so I'm suspecting there's a catch. Is there?

Yes if they're too big they have a downside but used sensibly, as they cut down on the total amount of prims needed, they can have a positive effect.

I tried 40 x 20 megaprim as my sky platform once. I use the platform mainly for building stuff but I found I couldn't rez things properly on the megaprim, so it was back to eight 10 x 10's.

There's still a ton of bugs associated with them unfortunately. Besides which, there are some optimisations which are currently impossible with them around, so I'm generally opposed to them.

However at the same time, LL has yet to offer us a viable alternative for building large shapes such as big spheres/cylinders that don't look crap.

One potential alternative I proposed on the JIRA was a "partial primitive" which is a small chunk of a larger shape, allowing us to build big shapes from the potentially more efficient 10 x 10 x 10 chunks. The JIRA issue is:
http://jira.secondlife.com/browse/VWR-2860

However, until something like that is available, a lot of builds will likely need mega-prims. I've recently come across a project of my own which is almost impossible to do without using mega-prims for one part (a big, strangely curved arch) as using smaller prims is unwieldy, very hard to texture and looks awful =(

1: They trash the Mini-Map, taking far more area and in a different shape than the actual megaprims. For example a 100 M long 0.01 thick, 1 M high megaprim going along a road at a 30 degree angle might show as a 30 M on a side square on the Mini-map. Place even a handful of megaprims in a sim, and the mini-map becomes largely useless as a way to see your position relative to the buildings in the sim.

2: Older megaprims had bounding boxes that often greatly exceeded their apparent size. This is because there were only a few of the originals, and most of the initially popular megaprim sizes were created later by severe dimple, path cut and other prim torture changes to the shape. For example, making a 50 M x 50 M x 1 m prim by dimpling a 50 M cube on top and bottom. People would place a megaprim "wall" on the edge of their parcel, not realizing (or caring) that the bounding box and the actual center of the prim was extending far into someone else's land, causing problems for them. (The more recently-created Megaprims tended to have bounding boxes that matched their apparenmt sizes, as the creators made a wide range of sizes to begin with.)

3: Megaprims can't actually be resized. If you try, they snap back to a max of 10 M on a side. This makes their usefulness in building somewhat limited.

4: Megaprims hae been reported to cause lag in a sim, especially if placed at the sim edge or if extending across sim boundaries.

5: It's harder to rez other prims on the surface of a megaprim, especially if that surface is where it is because of cuts or dimples that were required to reshape the megaprim.

Search the forums for "Megaprim" and for "HDM Prim" for a wealth of discussion on this topic.

Before Havoc 4 and some other clean-up, there were some significant problems with megaprims. Now, though, it's really hard to be sure which of those issues are just plain gone* and which may still be worthy of attention.

One problem that's just inherent to their size is the relative difficulty of working with these things, and the associated probability that in doing so, one will encroach on other parcels. This is especially true of the really huge old megaprims and ones that have been carved and dimpled so the origin is far removed from the "stuff" of the prim.

Knowing a little about how they interact with the physics engine, it's still best to keep them phantom when possible, to reduce collision calculations. The less carved-up and dimpled they are, the better, and the less complex (e.g., a twisted and tapered mega-torus is just going to be laggier than a simple mega-box with similar dimensions).

It's probably still a bad idea to make them Physical. (I've broken this rule for a smaller megaprim box, made it llMoveToTarget back and forth, and watched sim physics statistics pretty carefully--couldn't see any ill effects, but this is one of those "don't try this at home, kids" experiments.) They tend to be so massive that most fun physics stuff won't work with them anyway.

I try to avoid spanning region boundaries with megaprims but others have reported that they're particularly useful for exactly this purpose, so YMMV.

There also seem to be more precision problems than one would expect for their size: Tiny gaps, overlaps, and misalignments will appear even when they're perfectly placed.

_________
*Some of the adverse effects that seem to be history include not being able to rez on megaprims (although still, exactly where stuff rezzes on a megaprim surface is not well-behaved); and hollow spaces not being treated as hollow in collisions, limiting their usefulness and resulting in weird "anti-gravity" effects.

theres some bugs but mayor ones have been fixed.
theres no problem whatsoever ti use them on a full private region.

Conifer, there was at a time problem with rezzing things on megaprims, but it's fixed now. (I submitted it as issue VWR-3190 in JIRA.)

Building on megaprims worked though - my workaround was to have 10x10 plate for rezzing things on my platform.

On Open Life, if you use the RealXtend viewer, it lets you make normal prims up to 100m x 100m using the normal build tools. I've tried it, it's interesting. If you log out and then log back in using a normal SL type viewer, the big 'super prims' remain in situ, but you can't make more or rez a previously made super prim from your invo, you need to go back to RealXtend viewer to do that.

I haven't checked whether RealXtend lets you make 100m x 100m prims in Second Life. I would assume it doesn't.

Ah, Domchi! I might re-investigate megaprims, then. Thanks.

The newly created Mega Prims work Great...I have 3 Large builds with them...My Main store, One of my Homes, and My Office...All work great...

There are 1000's of Sizes available...and have had no problems rezzing things on them...I don't use any Sim Size ones...just large ones to save Prims..and it reduces the flickers at seams...since you don't have all the 10x10 prims...I took a 180 Prim Office down to a 13 Prim Mega Prim Build...Take a look if you want at my store...and if you want to see the home built with them Just IM me sometime...

The Store is on my profile Picks ( Still Working on the Top level)

I've used quite a few, up to 70x70 on my land for floors, non-phantom and with no problems, I am gradually replacing my old megaprims (made by gene replacement) with the new type and with a much larger variety now available in sizes, they rock, only problem I have is a lot of the people who created/packaged them used different naming protocols so I have to rename a lot from "box 40*20*10" to "40x20x10" to find them in inventory search I just enter "x20" or "20x" to find the prim I want.
The new ones I have even hollowed to make buildings.

I love 'em! I had a skybox that went from 18 prims to.... 3. I have noticed a few minor issues. When you are inside a hollowed out megaprim you can't just alt-click on the wall and drag your mouse around. The camera will shift outside of the megaprim and won't let you look inside. You can alt-click on other prims inside it and move the camera around normally though.

If you path cut a megaprim and then stand on top of the path cut area sometimes your feet sink into it. It happens with one prim I have but not others.

My sky-buildbox is also made from a mega prim. One huge hollowed out box with a top and a bottom. 3 prims wewtie woo! I've had absolutely no issues with it other than the resizing thing.

I adore the mega prims! I made replacement parts for my shop when there was an *ahem* exploit that allowed us to do so.

With havok 4, I'm forced to ask: Which is harder on rendering and physics: a 40x40x40 or four 10x10x10's? As an illiterate in these things person, I'd assume the four 10x10x10's because there's four separate bounding boxes, more sides involved, and well, over all MORE. Whereas the 40x40x40 only has one huge bounding box and (when not tortured) far fewer sides.

That is a problem with normal prims, too. Any time you focus on the hollowed face of a prim, the camera is forced outside of the prim's bounding box, on that line of sight.

I love the newer megaprims and have jettisoned my old Gene Replacement megas. I generally just use them for floors, roofs, pathways, and the occasional long wall; for anything else I like to break up the lines with windows or pillars. I still avoid using megas larger than 40m, though, just as a precaution.

Downsides to Megaprims?

the mega prim penis is one that comes to mind

Actually four 10x10x10's would only fill 40x40x10.

You'd need 16 10x10x10's to fill the same space as one 40x40x40.

Anyone for 64?

you're right. I'm mathematically challenged.

What's the LOD issue?

Does anyone know the tradeoff between using megaprims and using normal prims? How many megaprims is too many?

I haven't come across any issues what so ever. Apart from finding the right one for the job.
I have also just gone ahead and built a 60x60x20 club building. Main building is a low 220 prims. Would have been 36 for the ground floor alone. Now 1. 12 for a flat side, now 1 etc...

These megas will, I believe, become readily makable by everyone at some stage.

If anything should be banned it should be RL cluster bombs.

Hmm, can you actually make a mega prim sculpty?

Asked of a male friend: "Is that a megaprim in your pocket, or are you happy to see me?"