[Opensim-dev] Prospective ODE physics changes

[Justin Clark-Casey]

This is a good point, though there are still some walking/standing avatars in meetings.  And as there haven't been any 
other significant physics changes recently or changes to the layout of WP (as far as I know) then from my testing the 
collision adjustment is really the only varying change.

On 04/01/12 00:21, Dahlia Trimble wrote:
> Would a Wright Plaza meeting even have multiple point collisions? Most (all?) of the active physical objects are avatar
> agents and they use capsule colliders rather than meshes. Also, most are sitting and the few that aren't are standing on
> or moving across a flat surface, probably far away from any vertex in a collision mesh.
> I suspect if you are seeing different physics statistics it's probably something else that's contributing to it.
>
> On Tue, Jan 3, 2012 at 1:32 PM, Justin Clark-Casey <jjustincc at googlemail.com <mailto:jjustincc at googlemail.com>> wrote:
>
>     On 02/01/12 20:56, Melanie wrote:
>
>         Hi,
>
>         On 02/01/2012 21:51, Justin Clark-Casey wrote:
>
>             I'm thinking of making two ODE related changes.
>
>             1) Replace the current ODE libraries in OpenSimulator with ones compiled using the older GIMPACT collider
>             instead of
>             OPCODE.  This is to address ODE crashes in simulators with more than one region as detailed in [1] and [2].
>               These don't
>             appear to occur with GIMPACT.
>
>
>         I'm not happy with that as a general decision. We should, if
>         anything like that is done, include both versions to give users the
>         choice. The OPCODE should remain the default in order to not
>         jeopardize existing setups and the GIMPACT libs can be copied in by
>         those experiencing the bug.
>         Many people don't run multiregion at all and would see only
>         downsides if this were done.
>
>
>     Multi-region is a non-experimental configuration that is useful to a large number of people.  In my view, it's not
>     correct for out-of-the-box OpenSimulator to continue with such crashes in the long term.  This hurts adoption and
>     ultimate long-term success/survival.
>
>     However, it just so happens that on scouring the Internet, GIMPACT is actually the newer collider, as per [1].  I
>     don't know why I thought it was the other way around - I may have misinterpreted something that somebody said.
>
>     Indeed, apparently for our common use case (mostly static objects), GIMPACT should perform better, so I was also
>     wrong about the performance issue.  However, as I said, in my own testing I haven't yet noticed any significant
>     difference and these questions are complex ones.  But it's certainly my experience that using GIMPACT eliminates the
>     ODE crashes in stress-testing, possibly due to something connected with [2] where global object caches are shared
>     between collision spaces.  But this is still a wild-assed guess (we can't use TLS as OpenSim crashes immediately
>     upon startup).
>
>
>
>             2) Reducing contacts_per_collision in [ODEPhysicsSettings] from 80 to something much lower, maybe even 1.
>               In my own
>             testing, reducing this number can halve scene physics time.  Normal avatar operations, such as standing on
>             prims or
>             walking up ramps appear to be unaffected even at 1.  However, more testing is probably needed to arrive at a
>             compromise
>             number.
>
>
>         This would greatly affect scripts using physics. I believe the
>         optimum would be 16-20, which would ensure that the scripting
>         maximum (16) collision contacts are always available.
>
>
>     According to [2], the maximum reported scripting collision contacts is 8.
>
>     Testing with 8 on Wright Plaza today in the Tuesday meeting seemed to greatly reduce physics scene time compared to
>     previously without any apparent loss of required fidelity (50ms with 18 avatars, albeit mostly sitting down -
>     unfortunately I didn't record previous week's numbers but they were higher.  Nebadon tested one of his vehicles).
>
>     Testing will continue on the osgrid plazas.
>
>     [1] http://www.ode.org/old_list___archives/2006-October/020664.__html
>     <http://www.ode.org/old_list_archives/2006-October/020664.html>
>     [2] http://groups.google.com/__group/ode-users/browse_thread/__thread/f38c56584c650536#
>     <http://groups.google.com/group/ode-users/browse_thread/thread/f38c56584c650536#>
>     [3] http://wiki.secondlife.com/__wiki/Collision <http://wiki.secondlife.com/wiki/Collision>
>
>
>     --
>     Justin Clark-Casey (justincc)
>     http://justincc.org/blog
>     http://twitter.com/justincc
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-- 
Justin Clark-Casey (justincc)
http://justincc.org/blog
http://twitter.com/justincc