Tim RitcheyApr 3, 2024
James Thomson

Does anybody have any tips for generating a concave CollisionComponent in RealityKit?

I have some fairly simple geometry I'm loading from a usdz which I'd like to add a nicer fitting CollisionComponent to for accurate raycasting, but the closest thing is ShapeResource.generateConvex, which doesn't deal with holes.

Apr 3, 2024 at 6:51pmWeb
Show threadMatthew FlintApr 3, 2024
@jamesthomson
If you’d chosen to model those famously-straight European bananas, you wouldn’t have this problem.
Show threadJames ThomsonApr 3, 2024
@matthew So true!
Show threadAlex RosenbergApr 4, 2024

@jamesthomson Just FYI, a collision mesh (as opposed to a primative) is very very slow.

Can you loosely fit a few primatives to your shape?

Show threadAlex RosenbergApr 4, 2024
@jamesthomson And last I knew, they hadn’t actually implemented cylinder collisions so those were meshes and thus slow
Show threadJames ThomsonApr 4, 2024
@alexr Not easily, it's a whole map of existing geometry, which I wanted to be able to work out exactly where a line was first hitting any of the entities. Trying it with a convex mesh for everything, performance is absolutely fine (for my purposes), I just want a slightly better representation of things.
Show threadStuartApr 4, 2024
@jamesthomson if it’s just a one off, can you generate the shape resources manually to represent the model yourself?
Alternatively you could create a simple 3D model that represents the shape you want without the holes (or multiple models) and use generateConvex on that
Show threadJames ThomsonApr 4, 2024
@stuart It's a large(ish) map of geometry, so it's not something I can easily do at scale. In SceneKit, I could just use a concave physics object, but that doesn't seem to be easily done here.
Show threadStuartApr 4, 2024
@jamesthomson Blender has a modifier to generate a convex hull of a mesh, is that an option? Otherwise you might need to wait until after wwdc, there’s a lot of catching up to do for RealityKit…
Show threadJames ThomsonApr 4, 2024
@stuart I don't know if it will be better than RealityKit's convex hulls, but I also don't know how to get that into RealityKit. But yes, agreed…
Show threadStuartApr 4, 2024
@jamesthomson ah, I took “doesn’t deal with holes” as not working, but yes would be a similar result I would assume. Apart from splitting the mesh up into smaller convex shapes to recreate a concave structure, I’m not aware of another way currently…