[Opensim-dev] Prospective ODE physics changes

[Adams, Robert]

> ...
> 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).

Looking at the code, contacts_per_collision is the number of collision points reported by ODE for each collision -- like a prim sitting on rough terrain and touching multiple places on the ground. Reducing the count to 8 means that no more than 8 contact points will be reported by ODE and, if there are more, you can't be sure you get the 'best' ones.

I suspect that most of the time there are only a few contact points so it doesn't make sense that reducing the number from 80 to 8 would significantly reduce the compute time. If it is the number of contact points causing the computation overhead then ODE must be normally returning more than 8 contact points. Is this really the case? Or is something else going on?

-- ra