[Opensim-dev] PhysicalPrimMax=32m Proposal: Regions.ini Default

[Amy Smith]

Dear OpenSim Devs,

Date: 15 October 2012

PROPOSAL TO CHANGE PhysicalPrimMax=32m
This proposes a change to Regions.in file default parameter: PhysicalPrimMax=32m
Old parameter was: PhysicalPrimMax=10m

This parameter defines the maximum prim size limit (in any dimension x,y or z) at which the prim may be recognized by the region as a physical object. If any dimension of the prim is larger than this limit, the prim fails to become physical.


DISCUSSION AT OPENSIM MEETING
At the OpenSim Meeting last week in Wright Plaza OSGrid, I proposed changing the parameter default to PhysicalPrimMax=64m.
However, after taking some data and doing some research testing various sizes and shapes of physical prims, I now propose PhysicalPrimMax=32m instead. 

BACKGROUND:
The maximum prim build size using v1 viewers in SL was 10m, but this became obsolete recently with v2 and v3 viewers going to 64m. There has been *no limit* on the size of a physical prim in SL using their Havok physics engine. A mega-prim in SL can be physical (I have successfully tested 1024x1024x1024 physical prims in SL). However, in OpenSim there is good reason to limit physical prim size, mainly due to the simulator physics load causing simulator FPS to slow down. 

WHY CHANGE?
Q: Why would we want to change this default value? 
A: The primary motivation for changing this is the growing popularity of PHYSICAL VEHICLES in OpenSim. Content creators for the OpenSim community must design their products for the most common default value limits.


WHAT TYPES OF VEHICLES REQUIRE 32m PRIM SIZE?
Built to-scale vehicles require prim sizes larger than 10metres: boats, ships, trains, buses, airplanes, aircraft, spacecraft, automobiles, and amphibious craft. Especially multi-passenger vehicles and vehicles using tortured prims or mesh or sculpties. Tortured prims (path cut, dimpled, tapered) are often used to achieve the curve shapes of vehicles, and this leads to larger prim x,y, or z dimensions (even when the overall vehicle size is less than 10metres). Mesh vehicles tend to require larger prim size; an entire vehicle can be made with 1 mesh model.

BEST PARAMETER VALUE?
32 metres is the proposed best parameter value. It is a compromise based on performance vs the value of having creative content. Certainly 10m prims are safe performance, however, 10m severely limits the existence of vehicle content. 

TEST RESULTS
In recent testing of free prims dropped to ground, it was found that there appears to be a "breaking point" in the physics FPS performance with physical prim size larger than 45 metres. When 64 metre torus shaped prims were tested, this brought the physics FPS down to a low level. But, when 32metre prim size torus prims were tested, acceptably good performance was achieved. Of course, physics performance varies considerably among simulators. 

DATA:
Please see collected data on size vs. shape on Physics FPS:
http://opensimulator.org/wiki/User:LaniGlobal#Proposed_Change_Regions_ini_Default_PhysicalPrimMax_10m_to_64m

CONCLUSION:
A proposal has been presented for a default change. The change would be from an obsolete, but "absolutely safe" default value, to a new value that is closer to the center of compromise in simulator performance, only when larger size physical prims are rezzed by users. The result of this change would yield a huge increase in physical vehicle content in the OpenSim Community. 

Respectfully submitted, 
Lani Global
(Amy Smith)

Founder/Content Creator, LANI GLOBAL SYSTEMS (tm)
Owner of Lani region of OSGrid, an OpenSim/HG 3-D Virtual Sci Fi World
http://twitter.com/LaniGlobal

hg.osgrid.org:80:lani





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