Question about Sculpties and Lag

question: Do sculpts cause lag?

Well that's the basic question anyway What I am trying to find out is relatively how much lag, in comparison to prim items. Let's say I have a prim shoe that has 15 prims for a total of 30 prims...how would that compare to a sculpted shoe with 3 prims?

And a sculpted skirt...how would a 2 prim sculpted skirt compare to a 12 - 15 prim flexi skirt?

I realize there are a lot of variables (textures, something about how many faces a sculpty has etc.) but if someone could generalize for me, I'm just looking for a basic idea.

Thanks!

Lag means different things. The meanings that I think are appropriate to your questions are:

Server-side / physics / sim lag:So - no, sculpties do not hit the sim any harder than any other prim would.

Client-side / frame-rate (FPS):
Now there was a time that people used to bemoan the existence of tortured prims because of the FPS hit they would have on the client. Those days seems to be gone now - in favour of dissing sculpties. A 15 prim shoe probably uses some fairly curved faces - a 3 sculpty version probably wouldn't render much slower than the normal prims. In fact, a well-designed sculpty shoe might actually render faster

Network lag:
A sculpty sends as much information over the Internet as a basic normal prim - AND THEN it sends it's sculpt texture as well. So there is some network lag here as an extra texture needs to be sent to your machine. But the impact here is only as bad as having one more (smallish) texture applied to any of the prims around you.

Others will no doubt throw in their opinions - but mine is: don't let concerns of lag drive your decision to use sculpties or not.
For regular geometric shapes - use prims.
For organic shapes - use sculpties.
For shapes in between, use judgment to decide which will look better.

Great answer, I thank you

In addition to Ben's great answer, let me help to quantify thing for you somewhat, regarding how sculpties affect client frame rates. They contribute to FPS lag in two ways:

1. Sculpties have a lot more polygons in them than most regular primitives. And the more polys are in a scene, the longer the scene takes to draw.

At highest LOD, every sculpty is made from 2048 triangles. Compare that with a cube or a cylinder, which have just 108 and 192 respectively, and the difference is enormous. Curvier prims such as spehres (528 polys) and tubes (768 polys) are heavier than the simpler ones, but they're still far lighter than sculpties. It's only when you start twisting them that they begin to approach sculpty levels. But of all the regular prims, only the torus has as many polygons as a sculpty.

By my observation, the "average prim" by usage has about 190 polygons in it. Therefore, you need roughly 11 regular prims on average to equal the geometric rendering hit of one sculpty.

Or to put it another way, if using a sculpty can save you 11 or more regular prims, then it's worth doing. The sculpty will be less of a drag on your FPS than the 11+ prims would be. But if the amount of regular prims you eliminate for each sculpty is less than 11, then you're losing out. A group of 10 prims or smaller will be less laggy than one sculpty.

Keep in mind I'm talking about averages. If the 10 prims in question are all twisted toruses, then of course the sculpty would be less laggy. Or if you're talking just cubes, well then you'd need 19 of them to equal the weight of a single sculpty. But on average, the balance ratio is about 11:1.


2. Sculpties can sometimes be a bit more texture-heavy than regular prims, since mutli-sculpty builds will often have a unique baked texture on each sculpty, and such textures tend to be rather large. With efficient use of regular prims, the texture load can be much smaller, since it's very often possible to repeat/divide a single texture across multiple surfaces.

Of course, the opposite can be true as well. If you put a unique texture on each side of a cube, the six of them will likely outweigh the one texture that would be on a sculpty.


The bottom line is this. Both sculpties and regular prims can easily be abused/misused, as can textures, scripts, or anything else. Inefficiency is possible with every type of asset in SL, and since 99% of residents are amateurs who don't know any better, most stuff that's made is incredibly inefficient.

Good digital art is about balancing artistry with understanding of the technology involved. Both are equally important. Neglect either one at your peril. A high performance (low lag) build that is of poor visual quality (ugly) is no better than a low performance (lag from hell) build that is stunningly beautiful. No one will want to visit either one. The key lies in learning to make things that both look good and perform well. And asking the kind of question you asked here is one crucial step in that pursuit. Just be aware that the answer to such things will never be a straight yes or no. It will always be "It depends on what you're doing and how you use it."

Thanks Chosen

Left out this discussion is the Prim Cost. If you are making furniture or other things to be rez'd in world, they can affect tier cost. While high surface counts cost render TIME, high prim counts cost L$.

Somewhere there is a happy trade off point...

Definitely a good point, Naletes, but since the original question was about lag, it's not really relevant. You're certainly right, though, that sometimes prim counts are just as important, if not more important, to the success of a build than poly count. Balance in all things is key. What is the "right" balance will vary from project to project.