Individual pair collision tests

[BigBob]

Hi, apologies if this is an obvious question...

Can anyone tell me what the most efficient way to do a single paired collision test is?

In my simulation loop, I perform one complete “collision world” test and from that I then have a number of paired tests to perform where I move one object slightly each time.

I know which objects are involved and that they are definitely close enough to not need a broadphase test.

Execution time is of the essence so I’m assuming repeatedly calling the full “performDiscreteCollisionDetection” after moving a single object would be a bad plan.

Looking in to it I was wandering if I can create my own btOverlappingPairCache and just add a single pair to it before sending it on to btDispatcher::dispatchAllCollisionPairs but I’d be creating a new btOverlappingPairCache for each test which doesn’t seem like a hot plan.

If anyone can set me on the right path I’d be most greatful.

Cheers,

[BigBob]

Just in case someone's thinking, "that's such an easy question he'll figure it out himself in no time."... um, I haven't.

Any suggestions would be most appreciated!

cheers,

[Erwin Coumans]

So you want to have a loop like the following?

Code: Select all

for each object
  move object
  find all overlapping pairs that include this object
  dispatch only those pairs to find new contacts

In that case, it helps if you keep track of a list of overlapping objects for each object. Bullet currently doesn't keep track of this, but you can add this. You can implement your own pair callback (see btAxisSweep3::setOverlappingPairUserCallback), and that callback you can update the list of overlapping bodies in each of the 2 involved objects. You can also check out Box2D (box2d.org). As part of its island management, it stores a list of overlapping objects in each object.
I might add support for such overlapping body list in each body for Bullet as well, but right now I'm flooded with other work.

Hope this helps,
Erwin

[BigBob]

Hi,

Many thanks for your reply, sorry for not responding I was side tracked onto a different project.

I've resumed what I was doing and setOverlappingPairUserCallback has given me the ability to control which pairs get sent off for near tests.

I'm still doing unecessary broadphase tests but it's such a low overhead it's not much of a problem and I'll dig deeper into Bullet when I get the chance if I really need the extra cpu cycles.

Cheers,