Hi, I've been running my game through the CLR Profiler and it's telling me that the two main allocations happening at run time are:

1) DigitalRune.Geometry.Partitioning.AabbTree

2) DigitalRune.Geometry.Collisions.ContactSetCollection

Both called from Simulation.Update. The second one comes from one of the internal Wheel methods.

Could you confirm that these are indeed generating garbage? If so, is there anything that could be done to alleviate it (apart from not using the AabbTree, which I will try in the meantime in case it does not affect the frame rate)?

(Note I'm using version 1.5.2 of Digital Rune Geometry).

Thanks

Well it's odd because according to CLRProf (on the PC) the allocations do not add up enough to produce more than one GC/minute, however on the Xbox the Remote Performance Monitor is showing like 4-5 GCs/minute. There is a first one shortly after starting a race (*) which freezes the game for a fraction of a second, and then the others are not really noticeable.

(*) I should mention that this first GC seems to always coincide with the first collision between cars... hmmm...

Also I'm explicitly forcing a GC at the end of the loading, so each race should start "clean". In theory.

Anyway I'll keep investigating, thanks.

I'm using the prebuilt DLL.

The terrain is a HeightField shape, and the car is the raycast vehicle, with a CompositeShape made of boxes and spheres.

About the fix for the wheels, better don't do it yet, let me investigate a bit further ok? Thanks.

UpdateContactInfo() contains the following line:

The original code uses GetContacts(CollisionObject) which produces garbage. Even if this method did not produce garbage, the LINQ method FirstOrDefault() would probably create garbage (an enumerator on the heap).

This method can be replaced by manually iterating over all ContactSets:

Further optimizations:
If we have many vehicles, it wastes CPU time if each wheel iterates over the contact sets. If this shows up in a performance profiler, then we could restructure the vehicle code: For example create a "VehicleManager" that knows all vehicles and that iterates over the contact sets only once per frame and updates all known wheels.

Ok. Here's the deal. I applied the fix to the Wheel source code, but the impact is minimal. The real killer for me is the AabbTree: if I don't use it, I get zero GCs, and if I use it, I get one 15ms GC every 5-6 seconds, and occasional 30ms ones. Not really noticeable most of the time, but still there.

Problem is, I must use the AabbTree. Performance drops to the floor without it. It is being used to partition a CompositeShape made of hundreds of boxes (I think I discussed that in another thread).

So my options at this point would be:

A) Try the other classes in the Partitioning namespace. Does any of them not generate garbage and is suitable for this case?

B) Write my own ISpatialPartition. Perhaps a simple grid would do, although there are quite a few members to implement.

C) Use a fixed version of AabbTree or similar that you may kindly provide ;) in source code form.

D) Live with it. My game is just days away from submission and I'm very wary of any major changes.

Suggestions welcome :)