[Opensim-users] Opensim Performance

[Dahlia Trimble]

A lot depends on where the "physical" (moving, rigid objects or avatars)
are relative to the static (non-movable) non-phantom objects. Collision
testing can be a significant part of simulation load. It generally happens
in multiple phases: a "broad phase" where any moving objects' sizes and
positions are compared to other objects to see if they are close enough to
warrant more precise testing, and a "narrow phase" where any potentially
colliding surfaces are tested. If your scene is set up so that you have
many complex collidable (non-phantom) static objects but all of your
avatars are not near them then collision testing load should be fairly low.
However if they are all standing on colidable objects made of hundreds of
small prims then collision testing load will be much higher. Some prims
and/or mesh models can have thousands of triangles which could each be
subject to collision testing.

In general if you have very complex objects it's probably better to make
them phantom and superimpose a simpler, invisible shape which can be used
for collisions. The mesh uploader in most viewers offers an optional
"physics mesh" which could be used for this purpose as well. However, if
simulation CPU load is not an issue for you then you could probably get
away with ignoring such optimizations although considering how content is
often repurposed it could be considered a best practice to use them.

On Fri, Dec 5, 2014 at 12:16 PM, Dr Ramesh Ramloll <r.ramloll at gmail.com>
wrote:

> Hello there,
> As I was reading about opensim performance on the opensimulator.org site,
> I came across these two recommendations
>
>    - Make as many objects phantom as possible. Phantom objects do not
>    need to be tested for collisions with avatars and other objects, reducing
>    physics frame time and increasing performance.
>    - Make as few objects subject to physics (e.g. falling under gravity,
>    movable by other avatars) as possible. Physics objects need a lot more
>    collision testing than ordinary non-phantom objects.
>
>
> I understand these appear fairly logical. I am curious though, are these
> differences really going to make perceptible improvements in user
> experiences? Are there any metrics that would say help us know when to
> start converting unnecessarily physical objects to phantom?
> Thanks
> Ramesh
> --
> 'Consider how the lilies grow. They do not labor or spin.'
> *Rameshsharma Ramloll* PhD, CEO CTO DeepSemaphore LLC, Affiliate *Research
> Associate Professor*, Idaho State University, Pocatello, ID 83209 Tel:
> 208-240-0040
> LinkedIn <http://www.linkedin.com/in/rameshramloll>, DeepSemaphore LLC
> <http://www.deepsemaphore.com>, RezMela <http://www.rezmela.com>, Google+
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>
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