Cannot read properties of undefined (reading 'primitive')

[Tirzono]

Issue: have two meshes that share the same geometry with a primitive. Remove one mesh and then add the mesh again. You'll then get the error:

Cannot read properties of undefined (reading 'primitive')

Codesandbox: https://codesandbox.io/s/falling-rain-pr3nlj?file=/src/App.js

To reproduce the issue:

1. Click on "toggle left": left mesh is removed
2. Click on "toggle left" again: left mesh should be added again

The issue was introduced in 64c1b2f by @CodyJasonBennett

I am not entirely sure if this is a bug. I think it is, because I believe that in vanilla three.js you can use the same geometry for multiple meshes, but let me know if you think otherwise.

[micha2it]

I stumbled upon the same issue, issue is gone when downgrading fiber to 8.13.0

[CodyJasonBennett]

This pattern unfortunately isn't very well supported atm, the work-around being to declare geometry or whatever is attached as a prop to the parent. R3F v8 sees instances 1-1 with their React node counterparts which can only exist at one point in the tree at a time; this relied on broken behavior where instances would hold on to previous nodes' state. I've tried to support this behavior since this is a design issue of R3F (#2294), but it required much larger architectural changes which are in v9. Object3Ds still can only be in one place at a time, but it will permit usage such as this and be limited to three.js hierarchy.

[Tirzono]

Thanks for explaining. So if I understand it correctly it's probably best to wait for v9 because in v8 it probably won't be supported?

[CodyJasonBennett]

Maybe, I'd have to cc @drcmda if this is a pattern we can support, but I doubt our ability to use graph structures when neither React or three.js support them. In your case, you can specify geometry as a prop and sidestep any degenerative behavior.

[CodyJasonBennett]

I'm fixing related crash behavior in #2906 which unblocks this use case. It's not very stable if you then specify props or remount it, so not quite solved, but it's a best effort attempt at clearing things up here.

[Tirzono]

Thank you for looking into it. I actually realised that a lot of use cases of primitive in my code base can simply be replaced by specifying it as a prop on the parent, so that solved a lot of my problems already. But I appreciate you're looking into this and looking forward to v9 :)