Broadphase rebuild about joltphysics

[jrouwe]

When you said "we do this", it wasn't clear to me, whether "we" referred to Jolt in general, or the game and how it integrates Jolt. Ie. does Jolt rebuild/optimize the broadphase automatically as needed already or not?

This is how Jolt does it in general, it's part of PhysicsSystem::Update.

In my engine, I am adding and activating bodies one by one, which you mention is pretty bad. Of course most of that happens in the first frame when the level is loaded. Should I keep track of this and trigger a rebuild at some point? Should I just rebuild the broadphase for dynamic objects every frame? Are there helpers to do this in the background as you do in the game?

After loading I would recommend calling PhysicsSystem::OptimizeBroadPhase once to fully rebuild the tree (this you can do from a background thread but take care to not modify any bodies while you're doing this). Also when you're loading objects, try to collect all bodies that you're loading and add them as a single batch. If you don't, things will still work but it will be less efficient (in the first few frames).

Also you mentioned that the navmesh generation may run for several seconds, but you said that you swap the broadphase trees at the end of the frame.

I don't think it takes a couple of seconds, I think I said it takes more than a frame. We keep the old tree until the next physics update. At that time we'll lock the broad phase (see BroadPhaseQuadTree::FrameSync) and wait for any query that is still ongoing. Only the broadphase query part of the navmesh generation needs to have finished by that time, after that we've collected a list of TransformedShape which we can use to query triangles without requiring additional locking.