[Opensim-users] Opensim Performance

[Mister Blue]

For BulletSim, collisions between terrain, spheres, and boxes is an easy
computation. Collisions with meshes is a lot more computation. For
instance, the OSCC conference has a whole bunch of high resolution (large
mesh) chairs. The CPU to compute collisions with them was noticeable. In
that case, all the chairs were set phantom to save CPU time.

In general, avatars on terrain or blocked structures should not create
noticeable overhead. When you add meshes, you might have to consider
phantoming some things.

-- mb

On Fri, Dec 5, 2014 at 1:32 PM, Dr Ramesh Ramloll <r.ramloll at gmail.com>
wrote:

> Thanks Dahlia :)
>
> On Fri, Dec 5, 2014 at 4:05 PM, Dahlia Trimble <dahliatrimble at gmail.com>
> wrote:
>
>> 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+
>>> profile <https://plus.google.com/103652369558830540272/about>
>>>
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>>>
>>
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>
>
> --
> '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+
> profile <https://plus.google.com/103652369558830540272/about>
>
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