[sldev] [ATTN-LL] Physics engine status update?

[Dale Mahalko]

Before making any claim that another physics engine is better, you
need to load up the engine with the same amount of collision-volume
data as a maxed-out LL sim to do a really fair comparison.

Any engine will look pretty if it only has to deal with a small number
of objects, as with Truck Dismount, which has fewer objects to spread
the calculations. Get the engine up to SL's triangle counts and the
holes will start to appear.


A static prim with physics turned off is treated as a collision volume
for anything else moving around. In Sandbox Island, that is up to
15,000 collision volumes for the engine to deal with -- and
potentially even more collision volumes can be in the sim if
temp-on-rez is thrown into the picture. (Imagine 5,000 objects that
each rez up a 10-prim temp-on-rez linked object.)

Since SL does things differently than a proper 3D mesh-editor and
doesn't go by triangles/meshes but an ephemeral "prim" quantity, you
have to include objects that approximate the same mesh counts as the
various SL prims. A cut, hollowed, adv-cut, revolved torus probably
has around 500 triangles.

Multiply that by your test-sim's prims, and that adds up to over
7,500,000 triangles across all collision volumes, to be processed
every 0.022 sec (at 45 FPS sim-physics).

A test like this will probably bring the Open Simulator to to its
knees, begging for mercy. ;-)