@yujiang.wang Thank you so much for keeping this going! The work you’ve done on it looks amazing, and is very useful to our studio 
We’re just upgrading from 5.4 to 5.6, and have added the 5.6.1 GPULM patch. I’ve noticed a few strange artefacts, that are behaviours/results I haven’t seen before.
Have you encountered this at all?
What we’re experiencing is:
- What looks like possibly compression or interference artefacts in the finished build.
- Phantom shadows, or sections of the bake that have different brightness’ to others, such as a bright rectangular strip on a wall.
- Extremely pitch black zones. These often seem to be quite near to some foliage-painted rocks, set to static.
We’re trying to isolate possible causes right now, which could include GPU memory (I’m testing on my backup laptop), something strange to do with distance fields (I would guess not, but a lot of the artefacts seem to have a 3D influence that approximates the object’s shape), or something a little deeper.
Here are a few features of the level that might have an impact:
- Our landscape has its lightmap resolution increased, and a couple of surplus tiles deleted.
- Part of the level sits underneath the landscape - reached by a tunnel through a masked hole in the landscape.
- The skylight and directional light are set to static.
- We have a number of static mesh actors with a strong emissive influence.
- We’re not using ray tracing proxies, but rather high-res meshes (that we discard during package). The same effects happened when ray tracing proxies were turned on.
- When I run the bake, it is possible to see the phantom shadows and lighting artefacts appear. The square lightmap artefacts appear after the encoding step.
- We’re pretty confident this isn’t a lightmap overlap issue, as we’ve baked with this level before.
- We haven’t upgraded the lightmaps yet, as we created them manually. Happy to take recommendations on this.
This is a new set of behaviours, that weren’t in 5.4 with stock GPULM. I’ll keep exploring to see what might have changed, but so far, it’s quite perplexing. I’ll also run some tests in other scenes, to see if this is level-based or environment/project based.
Has anyone else experienced anything like this recently?