Question Procedurally generate meshes only when needed by LoD Group

I use procedurally generated meshes for terrain, and would like to use LoD Groups.
But I'd prefer not to generate all LoD meshes at once, since the camera may never get close enough to some meshes to require LoD0 or Lod1.
Is it possible to only generate a low res mesh at first, and then somehow have LODGroup request higher res meshes only when they are needed?

 

Yes.

Seriously, roll some code, give it a try. You know the criteria for when you need the higher LOD, see what you can come up with. Test small, iterate, measure, see what happens.

But the answer is "Yes."

 

I mean, if I had the source code to LODGroup and could alter it freely, that would be a simple task. But since I don't, I feel like I would pretty much have to write my own LoD manager to accomplish what I want, am I wrong?

 

Wouldn't you just either put no mesh or perhaps a tiny stub mesh into LOD group things you haven't decided to generate yet? And when the Uniy LOD manager turns them on, you would make the mesh then, or else make it early enough that it doesn't cause a stutter? By now I imagine you have tried SOMETHING, right??

 

Sure, no mesh, that part is obvious.

This is the heart of the problem. How would I know that the LODGroup tried using a mesh that doesn't exist?
I could attach a script that checks it every single frame in Update() on every single GameObject with a LODGroup, but that would be very ineffective.

What I did do was actually write my own (very basic) LOD Manager, but I'd save myself a lot of work (and probably improve framerate) if I could solve this one issue with LODGroup.

 

I hadn't fiddled with LOD in a while and I thought the LODGroup actually enabled/disabled the GameObjects so you could just hook the OnEnable() / OnDisable(), but this is not the case.

It also appears to not manipulate the MeshRenderer's enabled status so that isn't useful to observe.

However, you can hook this method to know when something is going to be considered for rendering:

https://docs.unity3d.com/ScriptReference/MonoBehaviour.OnWillRenderObject.html

I just tried it by putting that on the three LOD sub-objects and during running, only the ones involved are called.

 

Im pretty sure it's handled natively to save interops. I wouldn't put a MonoBehavior with OnWillRender for thousands of objects. Depends on scale of things.