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

Dale Glass dale at daleglass.net
Thu Sep 20 01:42:35 PDT 2007


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.
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