We recently had a friendly-yet-furious internal competition at work, where the goal was to create the fastest broad-phase algorithm ever.

We slowly reached the limits of what we can do with a 3-axes sweep-and-prune (SAP), and so we were trying to finally move away from it. This is not very easy, as SAP is very efficient in typical game scenes. Unfortunately as the total number of objects in games increase, and game worlds become more and more dynamic, the SAP performance increasingly becomes an issue.

Several people attacked the problem with several (and very different) approaches. I submitted two entries: one was the multi-SAP (MSAP) broad-phase I previously mentioned; the other one is something I probably cannot talk about yet, so let's just call it "broad-phase X" for now. Long story short: this last algorithm won.

Out of curiosity, and since I had done it before with MSAP already, I tried it out in Bullet's "CDTestFramework" to compare it against Bullet's algorithms. On my machine the new broad-phase is a little bit more than 4X faster than any of Bullet's versions, and more than 2X faster than MSAP. Of course the relative performances of all those algorithms vary with the total number of objects in the scene, how many of them are static, how many of them are moving, how fast they are moving, etc. So there isn't usually a clear winner for all possible scenarios. Still, at work we tested those new algorithms in dozens and dozens of scenes with different characteristics, and this "broad-phase X" always performed remarkably well.

The demo is straight out of Bullet 2.78, compiled in Release mode with full optimizations and the SSE2 flag enabled.

The new broad-phase should be available in PhysX 3.3. Stay tuned! :)

- Pierre Terdiman
December 22, 2011