[ODE] Strategies for efficient collisions in a large world with few moving bodies

[Olex]

I use quadtrees without any problems. Not sure what your problem there, but
I get decent speeds with quatrees for collisions. I've tested up to 3000+
static/sleeping bodies with a dozen moving ones. dSpaceCollide* does not
show up on the radar at all for me.

On 1/17/06, Shamyl Zakariya <shamyl at zakariya.net> wrote:
>
> I recently stress-tested my engine and found via some profiling that
> it's spending 46.3 percent of CPU time in dSpaceCollide2 ->
> dxHashSpace::collide2 -> collideAABBs.
>
> Obviously, this is pretty disressing. The specifics of the scenario
> are a 20km square world ( using a single trimesh for ground ),
> populated with approx 4000 boulders ( only four boulder models and
> trimesh data instances ) and 4000 trees ( again, only four models and
> four trimesh data instances ).
>
> From what I've read on this list, I took the approach of making 2
> spaces, a "static" space, for objects which will never move, and an
> "actor" space, which is where my character ( a lozenge ) and other
> moving, bodied and not entities reside. Trees and boulders and the
> ground are all in the static space. Right now, the actor space has
> *nothing* in it except the character lozenge.
>
> In my World::step() method, after doing various bits and pieces to
> update game state, I step ODE as such:
>
>         dSpaceCollide2( (dGeomID) _staticSpace, (dGeomID) _actorSpace,
> this,
> &nearCallback );
>         dSpaceCollide( _actorSpace, this, &nearCallback);
>
>         dWorldStep( _world, deltaT );
>         dJointGroupEmpty( _contactGroup );
>
> My understanding is that by using two spaces, this should be pretty
> quick, since I'm not concerned with collisions between individual
> objects in the static space. My understanding is that by doing it
> this way, it'll just determine collisions between the actor space and
> the static space, and collisions between objects in the actor space.
> That said, I'm still getting 46.3% CPU time in the call to
> dSpaceCollide2.
>
> For reference, _staticSpace and _actorSpace are hash spaces. I've
> tried to use quadtree spaces, but for some reason I get *no*
> collisions at all when I do that. Perhaps somebody has a suggestion
> here?
>
> When I use a quadtree space, performance goes up significantly, but I
> get no collisions -- at all. Here's how I set it up to use quadtree
> spaces ( note, again, I get no collisions so I know I'm doing
> something wrong )
>
>         _staticSpace = dQuadTreeSpaceCreate( 0, vec3( 0,0,0 ), vec3(
> 10000,
> 10000, 1000 ), 4 );
>         _actorSpace = dQuadTreeSpaceCreate( 0, vec3( 0,0,0 ), vec3( 10000,
> 10000, 1000 ), 4 );
>
> Can anybody shed some light on this? And, can anybody give me
> suggestions as to how to speed it up, in general?
>
>
>
> shamyl zakariya
>      "obviously, you're not a golfer"
>          -- the Dude
>
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>



--
Oleksandr Lozitskiy

"To be without some of the things you want is an indispensable part of
happiness." by Bertrand Russell
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