BulletSharp object referencing

[JmD]

I am developing an electromechanical simulation application using C# and BulletSharp.
I have a class "MySimClass" which has, amongst other things, a RigidBody property and a CollisionShape property like this:
MySimObject.RigidBody (this is a BulletSharp RigidBody)
MySimObject.CollisionShape (this is a Bulletsharp CollisionShape)

After a DynamicsWorld.StepSimulation() I will iterate through the contact manifolds to get the ManifoldPoints, and from the ManifoldPoints I get things like AppliedImpulse, LocalPoint..., PositionWorldOn... etc. These values will then be used by the MySimObjects to which the colliding RigidBodies belong. From what I understand, the only way I can get a reference from a RigidBody to the MySimObject to which the RigidBody belongs is by putting a referens to the MySimClass into the UserObject of the RigidBody, like this:
MySimObject.RigidBody.UserObject = MySimObject;

and to get the reference from the RigidBody I do a cast like this:
mySimObject = (MySimClass)RigidBody.UserObject;

If this is the way to do it, I would think the casting affects the performance in a negative way. Is this performance loss not significant enough to be bothered about? If it is, is there a better way to get a reference from a RigidBody to the "owning" MySimObject?

If this is the way and the performance gets noticeably affected, I would like to suggest "typed" versions of the classes in BulletSharp containing UserObject members, so there would be for example a RigidBody<T> class and a CollisionObject<T> class.



Bullet and BulletSharp are indeed impressive projects, and I'm very glad to see the steady development.

Regards
///JmD

[anthrax11]

All the cast really does is that it checks that UserObject is of type MySimClass and then copies the reference, so I doubt that this will be a bottleneck.

A performance hit might occur if the types on both sides were not the same and type conversion had to be done. For example, if MySimClass had a base class MySimBase and we tried to cast the same object like this:
MySimBase mySimObject = (MySimBase)RigidBody.UserObject;
then it would have to climb the inheritance tree to check that the cast was valid.

Generics would get rid of the type check, but it's a small gain and would be confusing to those that don't use the UserObject.

Storing the reference in UserObject should be fine. Another way I can think of would be to use a Dictionary of <RigidBody, MySimClass> pairs.

I'd recommend running a profiler such as SlimTune (http://code.google.com/p/slimtune/) to see where most of the time is spent.

[JmD]

Thank you for the thorough answer. Profiling will definitely be one of the things where time will be spent on this project, so thank you also for suggesting SlimTune.

///JmD