Real-Time Physics Simulation Forum

Re: MOPP analogue

2010-06-16T18:44:53+00:00

* Use btCompoundShape with optional dbvt.
CON: ray and sweep tests don't use the acceleration structure (issue 25). Also, seems like a slight abuse of shapes; nobody will care about the combined inertia tensor, for example. Issue 25 looks easy for me to implement, but it _has_ been sitting around for a couple years -- is there some subtlety that I'm missing?

no subtlety, too few resources. Please implement it and provide a patch.

For the record, this is not a good solution because of http://code.google.com/p/bullet/issues/detail?id=348

Statistics: Posted by paul.dubois — Wed Jun 16, 2010 6:44 pm

Re: MOPP analogue

2010-06-13T03:43:33+00:00

We divide our large world into chunks and wrap all static collision for a chunk into a Hk MOPP. The broadphase contains only a couple static objects -- one for the MOPP, one with a custom heightfield shape.

There seem to be a few possiblilities to do this this in Bullet.

* Forget the container; batch-add all the static objects to the broadphase at runtime.
CON: Makes shifting the broadphase origin more expensive, forces us to build the acceleration structure at runtime.

If you use btDbvtBroadphase, all static objects go in a separate btDbvt tree. It should be efficient.

* Use btCompoundShape with optional dbvt.
CON: ray and sweep tests don't use the acceleration structure (issue 25). Also, seems like a slight abuse of shapes; nobody will care about the combined inertia tensor, for example. Issue 25 looks easy for me to implement, but it _has_ been sitting around for a couple years -- is there some subtlety that I'm missing?

no subtlety, too few resources. Please implement it and provide a patch.

* use btMultiSapBroadphase; add a SAP for each chunk of the world, containing only that chunk's static data.

Not recommended, btMultiSapBroadphase is unfinished an suboptimal. First option is best.

We could easily extend the btBvhTriangleMeshShape to accept all types of shapes. Its static acceleration structure is more compact than btDbvt.

Thanks,
Erwin

Statistics: Posted by Erwin Coumans — Sun Jun 13, 2010 3:43 am

MOPP analogue

2010-06-12T00:40:25+00:00

We divide our large world into chunks and wrap all static collision for a chunk into a Hk MOPP. The broadphase contains only a couple static objects -- one for the MOPP, one with a custom heightfield shape.

There seem to be a few possiblilities to do this this in Bullet.

* Forget the container; batch-add all the static objects to the broadphase at runtime.
CON: Makes shifting the broadphase origin more expensive, forces us to build the acceleration structure at runtime.

* Use btCompoundShape with optional dbvt.
CON: ray and sweep tests don't use the acceleration structure (issue 25). Also, seems like a slight abuse of shapes; nobody will care about the combined inertia tensor, for example. Issue 25 looks easy for me to implement, but it _has_ been sitting around for a couple years -- is there some subtlety that I'm missing?

* use btMultiSapBroadphase; add a SAP for each chunk of the world, containing only that chunk's static data.

So, a couple questions:
btMultiSap or btCompoundShape for static collision? Or something else?
Is there anything tricky I'm missing about issue 25?

Statistics: Posted by paul.dubois — Sat Jun 12, 2010 12:40 am