Weired equivalence calculation

[Mitchi Slafford]

Well*sigh* Hi, i found a not so nice bug within the equivalence calculation... i've created a meshwindow with the equivalence of 1 prim, now for my house i need a second and so i rezzed another one... but here comes the bug, when i link the windows the properties show me 2 prim equal to 1 prim and the object even took only 1 prim on the land.. shall not bother me... but when i link the windows with my house(made of 28 prims) the properties and even the land info are showing me that the house is equal to 295 prims and they are taken on the land. Ok easy and fastest solution to not link the windows.

Maybe someone could explain that so i can understand this, pls

[Imnotgoing Sideways]

That's perfectly normal.  Not a bug. ()

What you have is what I'll call "Fractional PE" objects.  I've been experimenting with them since the open beta.  Basically, a properly optimized simple mesh with simple physics will have a PE of less than 1. ()

But, the build dialogue treats the PE as an integer.  So, from having a PE from 0.01 to 1.00, the display PE will be 1. =^-^=

Get two mesh objects with a PE of 0.50 and link them together, the resulting PE will remain 1 after summing and rounding the linkset. ()

I checked with Charlar and he stated that this value will always be rounded in order to avoid confusing people.  So, at this point, it'll be up to the uploader to indicate the fractional value of the PE, if it's important. ()

You'll find it while uploading.  When you get your upload quote, look at the far lower left of the upload dialogue, you'll see PE displayed in a 0.00 format.  This gives you an opportunity to record the resulting fractional value in addition to simply cancelling the upload to pop back in to your mesh app and cleaning some details up in order to reduce the number. ()

Less is more! =^-^=

Here's the fun part.  As long as we continue to have this fractional PE, it'll be a boon for mesh building materials.  Sort of like, reinventing prims.  There's no super good reason to make an entire house out of a single mesh.  Right now, we have Box, Prism, Cylinder, Sphere... as prims.  Well, imagine building a house with Wall-2windows, Wall-1door, WindowFrame, DoorFanWindow "prims"... Nearly all having fractional prim values. =^-^=

Prefab makers, the old texture stores, and inworld builders with no mesh experience will still have great tools to work with, if not better. ()

 

Now... To address your GAIN in PE.  I'm assuming the rest of the house is made of regular prims.  Be it hollow boxes and various other things to be as prim-efficient as possible.  Well, here's the fatal flaw.  Prims are the most inefficient building materials on the grid.  Really, they're lag nightmares by default.  How else can we explain why games with apparently 10x the detail can get 100FPS on computers which can only get 10FPS in SL? (>_<)

So, when building with mesh, while exersizing efficiency and reducing the overall prim count... When linked to a regular prim build or adding scripts, the lag is taken into account and the overall score is changed. ()

My mindset is; while building in prims, the prim count is an old an innacurate measuring method of resource usage.  Mesh and PE is more along the lines of "LAG POINTS"... A far more reasonable score for the effect each linkset has on the server, network, and client.  Reduce ~that~ number by making more efficient prim-replacing mesh components, and watch lag fade away. =^-^=

[Mitchi Slafford]

Really thanks alot thats what i call a explanation, now i understand the technique behind the calculations. But anyways i build the house with normal prims gonna change that if i feel to

[WolfBaginski Bearsfoot]

I've seen reports of that problem, and this is the first time I've seen an attempt at an explanation.

I've tried making a simple building from Mesh, and Prim Equivalence can be quite low, but my Viewer crashed when I tried to upload. But think of this. You can use a hollowed box to make a wall with one window, exactly in the middle. Mesh lets you make two windows in the same component, or a window and a doorway.

One downside is that a Mesh object has a limited number of materials. There's a limit to how complicated you can make things and keep the texturing simple to do.

And remember, you can select several objects and save them as one inventory item. So the not-linking work-around isn't so bad.

[WolfBaginski Bearsfoot]

I've been doing a rather crude test, and linked two mesh objects with one ordinary Prim. Total Prim Equivalence is 5, for a basic house. It's as quick and dirty a model as you could come up with, but no weird stuff with the linking of Mesh and ordinary Prims.

I'm wondering if something got changed when Mesh left beta status. 

[Drongle McMahon]

The workings of PE and the rules for when it is applied are described in the KB and wiki (use the three links to download, server and physics weights).

Essentially:

1) PE is not used for a linkset with only standard prims and/or sculpties as long as they are all set to physics type "Prim". For these linksets the old system of one prim per object is used.

2) If any linked object is set to a different physics shape type, or if the linkset contains a mesh object, then the PE calculation applies to all components of the linkset.

3) The PE is considered to be for a linkset, even if it consists of only one prim.

4) However low the download and physics weights are, each linked object will contribute at least 0.5  to the PE. If any of the linked objects contains a script, all of them will contribute at least 1 each.

5) The simplest standard prims (such as simple undistorted boxes) can have download and physics weights less than 0.5, and can therefore contribute as little as 0.5, as can simple meshes.

6) Standard prims with rounded surfaces and those with substantial distortions or cuts can have very high physics and download costs which will be counted if the linkset contains a mesh. (I recently made a small distorted torus that had a physics weight greater than 14,000).  Setting their physics shape type to "None" will not reduce high download costs.

7) Thus unless your existing standard prim linkset consists only of simple boxes, linking a mesh to it is likely to cause a very large increases in consumption of the parcel prim allowance, which may cause the linkset to be returned.

8) In rare cases with only simple prims, linking a mesh may reduce the prim consumption.

 

 

[Feynt Mistral]

Prims really are efficient designs, if contrived properly.  For example, a cube prim should be only 2 triangles per side and all you really need to display them properly is a vector for their position, a vector for their scale, and a quaternion for their rotation.  Short and sweet to transfer over a network, and easy enough to render.  The problem is SL was based on vertex shading for the early part of its life, so all the prims are over-tessellated.  Cubes, at their highest complexity, are 32 triangles per side to even out vertex shading.

Since everyone now can do per pixel shading (except the intel crapics chipset users, but who cares about them) they really do need to be rewrought, but in the meanwhile any mesh prim you can make will likely be more efficient than a prim for rendering.  The rub is a 512-ish poly sphere will cost way more than a prim sphere.  When gigabit connections become standard in the world, we'll probably see that number change.

[Nalates Urriah]

There is an audio tape of Charlar Linden explaining PE calc's on Metareality. I have an index of the audio on my blog. You can skip right to the place where Charlar is explaining PE.

See: Charlar Linden Interview.

It may help to hear it rather than read explanations.

[Snippy Yifu]

To me this is still a bug, or at the very least, a big flaw in the design of PE calculation.

The other day, I was making a skybox, with a little garden. I wanted the garden part to look more realistic and natural by adding a sculpty to it that would just "simulate" natural ground uneveness. So I had 2 sculpts, linked to 1 normal flat box prim. PE: 3prims. So far so good.

But then I decide to set the Physic Shape Type of the sculpties to none, so the user can have his two feet on the flat box. At that point, PE was 40 prims...

So in the end, an object that is less weight to the physic engine cost more in PE... and you're telling me that's not a bug ?

[WolfBaginski Bearsfoot]

Going by the last Mesh User Group meeting, it looks as though the whole counting system is going to get reworked, and the idea of all Prims having the same cost will vanish. Maybe there's going to be some arbitrary costing for Prims and Sculpts, as there seems to be now. Maybe stuff made from simpler prims will drop in cost, but the complicated features (a one-prim spiral stair--how do they do that?) will be vastly more expensive. But where is the balance point? And texture sizes seem to be coming in to the equation.

I'm not sure that the "technical" Lindens realise what they might be doing. People have made complicated builds, using every trick in the book to squeeze something into the limits set by the current system.  The Lindens are going to have to do a few better job of publicising and explaining this change then they have of past changes, or half the landscape is going to vanish back into inventories, possibly as a confused mess of objects.

The same cost is apparently going to be used to replace prim counting, prim equivalence, and avatar rendering cost. Maybe the figures will work out. I rather doubt it. Maybe the Lindens can explain their plans.

And maybe the horse will sing.