Mega Prims causing excessive lag ?

my understanding of 3D Meshes is its the amount of vertices your graphics card
has to render which denoted the amount of lag they cause, hence a sphere having
say 64 vertices would cause more lag than a cube with 12 ( is it 12 ? cant remeber )

so given that why would a mega prim cause more lag than a normal prim seeing as it has the
same number of vertices, infact i would expect it to cause less lag as you would use a single
prim rather than say 4 so reduceing the number of vertices that are rendered.


i know they have stabillity problems with collison etc i was just interested in the lag issue

Hmm having built a 7 story building using mainly 20x20x.5m MegaPrims I can't say I have any noticable lag at all still on my old mainland sim, probably better if anything than if I had used nearly 4 times as many prims instead
I have had some issues with them going phantom occassionally when shift drag copying them

Ive never experienced any xs lag due to the use of large numbers of mega prims. Ive worked on builds as large as 1/4 SIM.

I wonder who introduced the idea of huge prims causing lag.
I think that huge prims actually reduce the lag by replacing a number of smaller prims, and by occulting what's behind them.

Put a whole region inside a phantom 256m box and both the region and the neighbor regions should benefit from a lag reduction.
It won't look great, so maybe you can texture it, but not with a 256mx256m texture !!!

The lag is being referred to is probably from the physics engine and server side more than client side. "Mega" prims cross boundaries more often and probably (I'm only guessing) have a larger footprint in the physics engine than several smaller prims. Even when not set to "physical" Mega Prims do still take into account physical attributes such as being a wall that cannot be walked through.

Ever set a small group of Mega Prims "physical" in an otherwise stable SIM (they do exist!)? Watch the SIM's server side stats go haywire. I've heard of some people having the infamous 256m x 256 mega prim still, and this prim alone has been know to shut down a SIM if set to physical.

Can't agree. I am a bit obsessive about sim stats, keeping an eye on what is going on at all times when I'm building, or installing scripts, or scripted items on my Island.

Initially I was very dubious of using them, and therefore was especially vigilant. Though finding the IBM island builds used them did reassure me somewhat!

I've used fairly large numbers of 'mega-prims' (40+ at a time) to enable certain projects that otherwise would have dented my prim allowance pretty badly and noticed no discernible difference to performance or stability.
Admittedly none of the prims in question have been set 'physical', 'phantom' or anything else fancy - just vanilla prims... And you do have to watch them going 'phantom' unexpectedly while manipulating them. Then there's the rather odd collision detection behaviour of non-rectangular 'mega-prims'...

At one point I had 'mega-prims' projecting well past the sim border - I 'iced the water over' with a selection of them and the effect was nicer with the 'ice' extending well past the sim border out over the 'sea' - the island was set up like this for over 3 months with absolutely no adverse effects.

Obviously this sort of thing wouldn't go down too well on a mainland sim, the surrounding sim owners would probably protest for a start, and I suspect the 'mega-prim in two regions' effect might cause problems. But on individual islands I can state with authority there were no measurable or adverse effects.

They seem a useful building tool, used sensibly.

I would expect huge prims to reduce server load, since they're simpler than a large number of smaller prims to create the same shape.

Of course, I wouldn't be at all surprised to learn that they cause problems when set to 'physical'. I didn't realize you even could modify a huge prim this way, and I wouldn't bother trying it anyway.

I agree that it's probably wise to keep them off sim boundaries, but Inigo's exception of icing the water nearby is an interesting one.

I was doubtful so I tried, I went in an empty island placed a 256m box at 128 128 380 and set it to physical.
I observed the simulator statistics while and after falling, time dilation, FPS and physic FPS were not affected at all, their values stayed near the maximum.

It would be nice to hear an official Linden statement about megaprims. I would hate to build something with them, and have it wiped out because they decided to enforce 10x10x10 one morning. It wouldn't go over very well with my clients.

Rookie question: I've seen big prims here and there, but is there someplace to get all or most that are available or to create them ourselves past the 10m limit?

Thanks.

A LL employee already stated that LL wants to avoid breaking users' content.
(I can't find the thread.)
10x10x10 is already enforced in the way that you cannot create huge prims anymore.


They are available for free on slexchange.com or in the huge prims group.
There is ≈ 16 unique huge prims, all other derivate from them, so don't buy the "90 huge prims" pack.

Go into wireframe mode (CRTL+SHIFT+R while debug mode is enabled) And rez a 40x40 giant prim and count the triangles. Now rez 16 10x10 prims to cover the same area and count the triangles, as far as what the client has to draw, it shoud be fairly evident.

For those who don't want to try, a giant prim on a flat face always has 12 triangles on a face, in sort of a pinwheel pattern. Regular 10x10 prims range from 8 triangles at a distance to 16 close up. So even at a range 16 prims in a 40x40 grid will cause you to draw 128 triangles, and close up you will draw 256. The giant 40x40 prim will only ever cause you to draw 12 per face.

Cory mentioned it briefly in a THM a while ago..

I'm still not sure what to make of the effects (or not) of these huge prims. I've used a couple myself for long walk ways or simple walls.
But, I have to say, ever since the person next to me plopped down a bloody great castle set on top of nine 40x40 village blocks, I can hardly drag my arse arcross my own darn beach. The lag is the worst I have ever seen. Walking, sometimes flying!, is an exercise in complete futility. Several have been removed and I think there are only three there now, but it's still hard to move! And, I'm running into invisible bumps and ceilings and walls here and there where I didn't used to. (and no, nothing appearing on transparent).

Have you considered its the castle and the scripts in it, not the huge prims?

If you used properly such as in the construction of walls/floors, road, etc, they do reduce lag. There are fewer prims which means less calculations for the server and fewer textures to load, just 4 vs 100 +

yep!

Dellybean anychance of a LM so me or some of the others
can take a look for ourselfs ?

just want to experience it for myself and
do some tests

hi Altic, yes.. here is a landing spot by my beach. The castle is situated on the SW quarter of the sim..just kinda look up (wayy up) you can't miss it
I'm actually able to walk not too badly at the moment, though I do seem to freeze in place for a minute on a regular basis.