Partial GPU Lightmass Build

I’m using GPU lightmass for a project with UE 5.1.1 and an NVIDIA RTX A4500. I’m fairly new to unreal, and had been setting up this project to use lumen/nanite, but couldn’t get the framerate I needed, and CPU lightmass was giving me weird results.

I’ve noticed with CPU lightmass, that if I change something small in the scene, i get the message saying “x number of objects unbuilt”, and if that is a low number, the build is fairly quick. However, GPU lightmass seems to do a complete build everytime. Is there any way around this, aside from switching to “bake what you see” mode?

Not directly, but I could recommend some tips and tricks.

You could always use alot of levels/sub levels, and bake them each, and thereafter (once you want all the levels together) you could make it into one level by just copying everything or adding everything into one master level (you could use “Levels” in Windows->Levels for this) - I’ve done this in projects where we used CPU lightmass in UE4, but it’s works the same.

For development I suggest that you lower the samples for the fastest calculations, if it has 4096 GI samples, go down to 1024 or even 512, puf you can even go down to 256 in some scenarios! Keep in mind, nothing needs to be perfect in development.

I’ll see if I can get the quality down enough for a decent build time. I’m not sure sub levels will work in my case since it’s all one environment I’m working on.

I’m using UE for XR/Virtual Production, and sometimes we just want to move a background prop to better compose a certain shop. Frustrating when that requires a full rebuild.

I think the plan is to just get a powerful enough rig where we can use Lumen instead.

Yeah in case of using XR/VP, I would definitely recommend looking into getting a better rig and use Lumen instead. Good luck with that!