Are megaprims laggy?

there could be a financial reason for not allowing them as well..
prim limits on land.
i would be curious how it would affect the need to upgrade to more land to get more prims..
God knows i've bought more for that reason than any other hehehe

Speaking as a builder, and as one of the people responsible for the creation of 329 of the "new generation of Megaprims", one of the earlier posted hit the nail on the head with the observation about most of the Gene Replacement megas being the size they appear because of cuts, dumples, and other "Prim Torture" tricks.

ANY prim in SL that is not phantom and has a bounding box which is noticably larger than its functional full shape and visible surface area will cause lag effects when you are inside that prim's bounding box area, because the SL client has to keep recalculating for "Hold on! You're inside that prim's bounding box! Oh, wait, haven't reached it's effective surface yet, keep going. HALT! You can't move now, you reached its effective surface.".

You can even do it with regular 10 x 10 prims. Take a 10M cube, change it to a sphere, and dimple it 45% from top and bottom. Now make it a box prim again, and you have something flat, like a wall. But the bounding box still extends to either side of the thin apparent dimension to the limits of a full cube. Now, try building a house with a bunch of those for walls. It will be laggy as hell to be inside or close to that monstrosity, even though there's no megas in it.

Same goes for using lots of non-phantom sculpted prims that are poorly made, with bounding boxes far larger than the actual visible surface. If you are "within" the bounding box area, and the prim is not Phantom, it can and will cause lag issues. This is one reason most sculpties are phantom.

And if the prims are also Physical, there's even MORE calculations needed. Though Havok 4 helped a lot with that.

Well, with the Gene Replacement megas, that sort of manipulation is precisely how many of the apparent sizes were made. So what looks like a 100M x 100M x 1M wall pabel still has a 100M cube for a bounding box, and adversely affects anything within 50M of the wall's center point.

A friend of mine in Bay City had a nice parcel, right out on the edge of that block of sims. When she set up her shop, lag was normal. Then one day a 50 M tall, perpetually empty "office building" appeared on the parcel right beside hers, and her lag went through the roof. I came by and inspected the offending build. It was entirely made of Gene Replacement's megaprims, all prim tortured to be less than their full size, and many of their bounding boxes overlapped her entire store. We AR'ed the owner for megaprims on the Mainland and for parcel encroachment, and after months and months, the offending megaprims were finally removed. Her lag situation returned to normal levels again as soon as it was gone.

Now, if that same build had been created using the newer generation of Megaprims, THOSE have many size choices that would have needed no alteration of apparent size at all to do that same build. Their bounding boxes could have remained firmly tight to the visual surfaces, and entirely within the parcel they appeared to be in. A build like that probably would cause no noticable lag at all.

Well this is all good to hear.

My new 'soon to be club' is basically build inside of a mega-sphere in 3 cuts.

2 21x21x21 megas make the top and bottom, and a 21x21x5 makes the center wall, with a 20x20x1 as the main floor and a 10x10x.1 as the basement.

All wood textured, with assorted mushrooms and roots, and a few branches sticking out of the side at visible entry spots (not enough prims to go wild, so I had to be selective).

Voidicus at I think... 16/18/3500.

Its not a very fancy design, and that's kind of on purpose - to be homey / cozy rather than cool / sharp.

But I was worried about those megas after hearing and thinking on comments about megas.

My home / shop skybox also uses a mega for roof and floor: 15x30 I think, just a tiny fraction under the typical 512 plot size so that I could squeeze in a stairwell and get a 3 floor structure on as few prims as a design I liked could afford (screenshot in sig - at 1710 on any plot I own... no Idea why I like 1710m up. - I think just because back when Fietzo was more crowded, it was the 'empty zone').

My cloud cafe uses a build similar to my club and does get laggy - but it has more sculpties than it should (I keep thinking of deleting about half the chairs in that place), and is right at 220m up in the thick of the clouds. So I assume the clouds are a good half or more of its lag.

One difference I know of with some of the older megaprims is that you could not occupy the inside of a hollowed megaprim unless you set it to phantom. That is not a problem with the newer ones.

I recall those places. It was pretty harsh, that!

/me nods... even when the GR megas were all we had, I was reluctant to use any of the tortured versions. So I labelled all the copies I had as 'base' for the untortured ones (8 of them, at a quick count) and only used those.

The megas on my land are listing a "Zwagoth Klaar" as creator.

Should I be looking for "Genetic Replacement" as the problem ones?

Not necessarily - if what's been said here is at all valid, *any* sliced and/or cut mega could be the culprit. Modern megas come in a better range of sizes, so are far less likely to need slicing to get the right size. The GR megas were sold/given away in their sliced and cut forms, usually (in my experience) labelled with their apparent sizes.

That said, lag comes from all kinds of sources and there's no guarantee it's being caused by any megas.

It's "Gene Replacement". And as the previous person mentioned, it's the fact that Gene's megaprims got redistributed in so many tortured sizes that makes them an issue. He only made a handful of actual sizes.

When we had a brief chance to make new ines, Zwagoth, Carl Metropolitan, and several others, including myself, made as many unique and hopefully useful sizes as we could thing of, so people could have an unaltered megaprim in the size they needed.

But if you take a 50 M cube from my set, and warp it around the way people did with Gene's original ones, the tortured version of mine will have the same problems as Gene's.

Gene's name is sort of a red flag, but only because it is so likely one of his that you see has an altered size. But what you really need to pat attention to is the bounding box. If that bounding box (the white streach handles in edit) are neatly at the corners of the prim, and its center is at the visible center of the prim, it's probably OK. If the bounding box extends far beyond the visible surface, and/or the center seems offset to an edge or corner, it's been tortured to that visible shape from something larger.

So if I take a mega box.

Make it a half cylinder (path cut end .5)
Make it 95% hollow.
And then cut out an 'arch' on one end (dimple .042)

That's going to drive up lag?


Like this:



- Roof of my club.

Unfortunately, you'll probably have to try it and see.

When H4 was new and non-phantom megas were first considered "safe", I lived for a time in a sky build shaped a bit like that picture. It was a huge, squashed hemispherical dome that I cel-shaded just for kicks. Now, I didn't have a lot of visitors, but there seemed to be just enough physics lag whenever they arrived that I got nervous and eventually made that dome phantom and added transparent non-phantom box-prim walls ringing it. Of course, that may have all been superstitious, and anyway, YMMV.

But people who alt-zoom and alt-control-swivel their cams are going to *hate* being inside that dome. That's ultimately why I abandoned mine. Pulling the cam back, it's easy to get caught outside the dome, and it's a bitch to get back inside. Also, pulling the cam from the hollowed inside of the dome is fraught with peril: sometimes it works, and sometimes it behaves in some wildly unpredictable way.

as Qie noted focusing issues can become a hassle, and I have an idea as to the physics issues....

hollows and cuts for anything increase physics processing for anythiing within the cut/hollowed area, because the broad phase detection on physics interactions uses the original bounding box before any cuts or hollows are applied.

Andrew Linden suggested that overall this shouldn't be much of a difference since most of the narrow phase processing will be valid, but may have only been referring to uncut/unhollowed mega's such as platforms, walls etc; where there is not a high amount of traffic in the cut areas. H4 seems much better at handling this than H1, but I think it still might be an issue.

my suggestion (and I know how much it sucks for some builds) is to always point hollows and cuts AWAY from areas of highest traffic, for the best handling by the physics engine. If you don't... well that's on you, but I wouldn't be surprised if LL eventually comes down on it.

ETA:
which is basically what Ceera has been saying, so I apologize for skimming and repeating the same damn thing =P

Where it will be a problem in particular is if you walk through the area that would be occupied by the shell of the sphere that has been removed. So when you go through that door arch, you'll have some lag. Or if there is space below the rim of the dome, like a lower floor, or the room has a cylindrical wall below the dome rim, then the area that would be impeded by the cut-away lower shell would have some issues. Fortunately, it seems to behave more nicely with a "hollow" effect, as it seems to understand that the well-defined (and simple to calculate) void left by hollowing the prim is a space it doesn't have to worry about. It's the area removed by path cuts, dimples and the like that gets strange.

You could make a less problematic roof by making that roof phantom, since then the client doesn't care if you are colliding with it or not.

And as was stated, any time you point a camera at the inside wall of any hollowed prim, expect strange behavior from the camera. Example: Make that dome, and put its rim flat on the ground. Walk inside. Try to zoom your camera at the inside wall. Your camera pops OUTSIDE the dome, on an axis straight behint the camera's position and angle of sight, point-blank to the exterior surface of the prim. That is a known glitch in hollowed prim behavior that LL has beed incapable of fixing for years. The camera zoom assumes the prim is solid, and that the camera can't be inside a solid prim.

That is not so much a problem of batch but rather of the old havok1 and new havok4, keep in mind that when you are inside a hollow prim, no matter it's size, you are inside the bounding box.
Another difference many have noticed with the introduction of havok 4 is that you can get stuck inside a solid part of a prim, if the prim is smaller then the boundingbox of the avatar you get stuck in place and in the falling animation, if the prim is bigger you can actualy walk around in the inside of it.
I haven't tried if you can create this condition on purpose.

The building is basically 2 of those prims, and a prim in the middle of them that is a regular cylinder, with a cut where the arch is to walk in. And a cylinder floor:

http://slurl.com/secondlife/Voidicus/37/16/3501
- That will show you what I've made.

If I need to re-build, going to be annoying, but good to know early.


.

Just a few like that won't be too bad. The killer is when there's dozens of the things, all with bounding boxes overlapping in apparently unoccupied volumes of space.

I wouldn't worry too much about just three, in that configuration. But if you can make the spheres phantom, it may help reduce lag.

There's a script trick in the forums recently for how to use the "volume detect" property to make a prim act phantom, but still be linkable. Send me an IM in-world, and I'll send you the script, and an example wall that has a phantom central part in a three-prim linked wall.

Yeah I was thinking of making the top one phantom (or even losing it for open sky, but that cuts into the cozy theme). The bottom one is used for a sort of 'funky smoke room' under the club floor, so if it becomes a problem I'd have to kill that room or reshape.

please note that while that trick for using volume detect will cut down on some of the physics handling, it won't eliminate it like making it phantom does (collision is still triggered it's just not being applied to physical objects, but it does generate events in all linked prims, which must be handled by any scripts that have collision sensors)

hi just wanna to say i love megas prims. if they make lag iam waiting for it .Sl lag without megas prims . i use them none stop and i cant tell if they do lag for me .

Here are some shots of the design and how I've got megas in it:



The basement might be laggy. That is under the dance floor, and there is a similar room under the grassy landing area.

#6 shows the inside of the dance club, with the floor 'cutaway' so you can see the basement under it.