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

[nik at terminaldischarge.net]

Hey

> On Thursday 20 September 2007 02:38:20 Dale Mahalko wrote:
>> 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).
>
> Why would it test for collisions on triangles?
>
> Prims are ideal for collision testing. Testing for collisions against a
> mesh which happens to be a sphere would take a lot of processing time,
> while checking against a sphere prim would be near instant in comparison
> since as you KNOW it's a sphere you can do the check against an imaginary
> perfect sphere.
>
> In fact, I thought this was a major reason to use the prims concept: If
> you
> specify the shape and its characteristics instead of a mesh you can
> generate as few or many triangles as you want (scaling with available
> processing power) and calculate collisions much more efficiently.

What happens if the sphere a dimple or has been turned into a torus?
What happens if the sphere is cut?
The reason for prims, was so they could send shapes that, even after some
fiddling, might have complex meshs, as just a few parameters across the
network. Rather than 100's of vertices, they send 20ish parameters.
Lowering network bandwidth usuage and allowing the streaming of objects
you see.



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Nik.