Trimesh-trimesh collider (was Re[2]: [ODE] Triangle-box collider contribution)

[Nguyen Binh]

Hi Jeff,

JS> How did you test it?  What step function/stepsize did you use?

    I used the test_moving_trimesh.cpp in CVS.
    It drops a bunny over two bunnies.
    The WordStep with 0.03 stepsize behaved completely unbelievable.
    The StepFast did better but still let many penetrations.

    Then, how did you test it? StepSize, number of contacts and what
    mesh did you use?

JS>  How  many contacts did you allow the collider to create?  I've been having
JS> very good (although certainly not perfect) performance when using
JS> dWorldStep, a step size of about 0.5 msec and up to 128 collisions.
JS> Stacking trimesh objects still causes problems, for reasons I haven't
JS> been able to track down, but "simple" collisons between multiple
JS> trimesh objects works just fine for me.

>> But everyone knows tris-tris is amazingly hard so the first brick is
>> very important!

JS> Actually, given the current architecture of ODE, it's basically
JS> impossible to do trimesh/trimesh collisions "correctly". With some big
JS> changes to the way trimeshes are represented, I think we could do a
JS> convex decimation/GJK approach, which is what Havok, Maya and others
JS> use.  However, the amount of work involved in this solution is so
JS> large that I chose a more "heuristic" (i.e. wild-ass guessing) method.

    I cannot agree with you more. Convex geometry is really needed
    now.
    
JS> Currently, I just set the mass based on the bounding box of the
JS> trimesh. A more "correct" approach would be great, but remember that
JS> it has to handle solid vs. hollow objects as well as polygon soup
JS> meshes (i.e. meshes with no particular notion of "inside" and
JS> "outside."

    No problem! I use the method described by Brian Mirtich. It can
    handle any closed mesh.

    Thanks for your amazing works Jeff!

-- 
Best regards,

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   Nguyen Binh
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   Glass Egg Digital Media
   
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