Linden
Posts: 157

# Calculating "Prim Equivalency"

Greetings all!

There's been a bit of confusion around how we deecide how many "prims" a given mesh is equivalent to, so I wanted to take a moment to go over the system from a high-level view to try to clear up some of the confusion.

Prims that are subject to these rules fall under one of the following categories:

1) Its a mesh

2) It uses the new physics shape type

3) It is linked to #1 or #2

Anything else will fall under the legacy system of 1 prim = 1 prim.

For content under the new system, we measure the content against three metrics (or "weights"). These are: Download weight, Physics weight, and Server Weight. Once these values are computed, we take whichever one is highest and treat that (rounded) as the number of prims charged against your land's budget.

• Download (streaming) weight depends mainly on the number of triangles in a primitive (mesh or not), as well as its physical size. This is to account for approximately how complex the object will be to download & draw at various distances from the object.
• Physics weight depends on the physics representation used (prim, convex hull, none), as well as how complex that representation is. Note that "Prim" physics shape type could refer to an uploaded convex decomposition, or an undecomposed physics mesh.
• Server Weight tries to approximate the amount of messages that a given object will generate on the server that has to be passed to observers. There is a per-object (linkset), as well as a per-primitive cost (a single unlinked prim counts as both). Physical and scripted objects generate significantly more messages than static content, and thus are charged more in server cost.

Please note that the different weights are computed completely independently. Specifically that means that adding a script or making an object physical will affect the Server weight, but will have no effect on the Download weight.

I'll be working on trying to update / keep up to date the costs and fees page with the latest information. https://wiki.secondlife.com/wiki/Mesh/Costs_and_fees

Please note that we are still working on adjusting the exact numbers being generated by each system, so if you have content that seems too heavy or too light in terms of prim equivalence please send it in. We believe the current structure should be a straightforward system for the first release, though we reserver the right to make changes as appropriate in the future. Please let us know if you have questions!

-Nyx

Posts: 1,437
Registered: ‎06-15-2010

## Re: Calculating "Prim Equivalency"

Reply to Nyx Linden - view message

I noticed the costs display in the edit floater changed on the latest Mesh servers. Is it now this number we should take as prim count, or should we still go with the Show Render Info > Selection Streaming Cost display?

Posts: 1,988
Registered: ‎06-30-2009

## Re: Calculating "Prim Equivalency"

Reply to Nyx Linden - view message

If i have only one single object, then i sometimes see the costs for the link set and the costs for the object differ. Which of the 2 will be the final value to take care about ? Or will it be ensured that for one single object the costs for the linkset and for the object are always the same ? why would they be different for one single object at all ?

the mesh weaver
Linden
Posts: 157

## Re: Calculating "Prim Equivalency"

Reply to Nyx Linden - view message

Linkset (Object) cost should be the one that you are actually charged against. We're going to be cleaning up our build tools display of data soon hopefully. The only difference between the two should be that the linkset cost should be rounded from the total prim cost for a single object.

Posts: 3,454
Topics: 41
Registered: ‎02-25-2009

## Re: Calculating "Prim Equivalency"

Reply to Nyx Linden - view message

So. I make a building out of 99 meshes (I have to break it up to keep the streaming cost down) these are simple small pieces with streaming weight 1.0 each. But my server cost is now 200. Oh well, it will still fit on my 1024m. Oh, I forgot, I have to put a script in the door that opens it in response to a touch. It's a simple script because I used my work-around to get the pivot at the hinge. What! the cost is now 400! It got returned! Oh well, I'll buy some more land.

Now I may as well put half a dozen of my favourite scripts in each of the 99 prims. I'' have them tell me who goes near them with a sensor and sending http messages to my database. I'll make them switch textures in response to commands on an open channel. Some of them can have streamed media on. After all, that won't cost me any more than the door script. Oh.

Even better, I can sell that extra land. I can attach the whole building to a bot and still have all the prims left. Time tier down to a 512.

In other words, the suggested implementation of server cost bears no relationship to the actual server burden. It's only effect is yet another step to make meshes unusable for anything except attachments. If this is the plan, then please tell us, so we can stop wasting our time. If not, then at the very least make it a per-script cost, although I suppose scripts can still vary in server burden by orders of magnitude.

Unless otherwise stated, any viewer-related information refers to the official LL viewer.
Posts: 1,092
Topics: 23
Kudos: 105
Registered: ‎09-23-2009

## Re: Calculating "Prim Equivalency"

Reply to arton Rotaru - view message

arton Rotaru wrote:

I noticed the costs display in the edit floater changed on the latest Mesh servers. Is it now this number we should take as prim count, or should we still go with the Show Render Info > Selection Streaming Cost display?

I'd have to echo Arton's question. Should we still look at streaming cost for the most accurate indicator or prim cost versus the edit floater?

SL Mesh Video Tutorials: All SL Mesh Videos | SL Rigged Clothing Series
Posts: 59
Topics: 3
Kudos: 1
Registered: ‎06-24-2010

## Re: Calculating "Prim Equivalency"

Reply to Nyx Linden - view message

We hear a lot about prim costs and rigging in this forum but I have only one question...  Will we, or will we not be able to build Mesh vehicles that have as much detail as today's sculptie ones?   Anyone have any insight on this?   TY

Member
Posts: 110

## Re: Calculating "Prim Equivalency"

Reply to HD Pomeray - view message

HD Pomeray wrote:

We hear a lot about prim costs and rigging in this forum but I have only one question...  Will we, or will we not be able to build Mesh vehicles that have as much detail as today's sculptie ones?   Anyone have any insight on this?   TY

No, i dont think so. With the last correction to streaming cost, i doubt it will be possible anymore.

You can still do it, if the vehicle is an attachment, thought

Honored Resident
Posts: 56

## Re: Calculating "Prim Equivalency"

[ Edited ]

Reply to HD Pomeray - view message

There is at least one highly detailed mesh vehicle around; arton's land rover. Has had a prim cost as high as 160; currently has a streaming cost of 80. It drives great. none of it is an attachment. There is currently a copy of it in sandbox 21 and meshHQ 3

Posts: 1,437
Registered: ‎06-15-2010

## Re: Calculating "Prim Equivalency"

Reply to HD Pomeray - view message

Well yes, since the prim count and the physics count are seperated with mesh, you can build highly detailed mesh vehicles, and they will still be physical as long as the Physics Costs are 32 or less. The Prim count can be 5000, or something, if you want.