Hi there. Can anyone explain to me what is happening with my shadows and why they are flickering so much? Is it virtual shadow maps or something else? It only seems to happen in areas of complete shadow or heavy indirect lighting. If I add more lights or more indirect light bounces it seems to go away. I’m struggling to find a an explanation to this phenomenon.
Video linked to show the flickering in question.
Hi @GBreezy1, I can explain this for you!
This is a part of lumen. You’re very right- this is going to be worse in shadowed areas with a lot of indirect lighting because this is where the effects of lumen are most visible. You are also correct that adding more indirect light bounces helps this problem. Lumen by default does not make room for many multi-light bounces, since this gets costly very quickly. This page from Epic goes into detail on how Lumen works as well as common issues, including yours: Lumen Technical Details in Unreal Engine | Unreal Engine 5.5 Documentation | Epic Developer Community
There are a lot of potential ways to fix this problem, but they are all going to come at some form of an increased cost. You can add more lights into that area, adjust the Lumen Scene Quality and Lumen Scene Detail in your postprocess, adjust the Final Gather Quality in your postprocess, or run some console commands to adjust various Lumen settings, though make sure you know what you’re doing before playing around with them (you can go to this page and type in “Lumen” to get a full list of commands https://jandusoft.github.io/)
Hi @sarahlenker,
Have you ever encountered an issue with hair rendering? I’m experiencing some noise in my Metahuman hair. I’m using 32 samples for the light with ray tracing off, and I’ve tried several CVRS for the hair. In another thread, Epic staff mentioned that the issue might be related to raymarching and suggested using certain CVRS (you can find the thread here, but the problem still persists.
Additionally, from my testing, it seems that the backlight in my scene is causing some weird flickering. I’m wondering if you have any insights into what might be causing this.
By the way, thank you for sharing that website with the list of all the commands and console variables in UE in your reply—it’s been super helpful!
Hi again @cgace!
I personally haven’t encountered this issue, and am having difficulty replicating it on my end. However, I have a few ideas of what could be happening here.
This thread seems to describe the same problem you are encountering, and you mentioned having adjusted some hair cvars, which makes me hopeful the solution from the thread may also help you: Weird Hair Groom Camera Shadowing Artifacts/Glitch - #4 by Adithya15
If this doesn’t work, I’m wondering if it may be your light itself. Rect lights and point lights start to display some pretty bad banding at large attenuation radiuses, though admittedly normally this problem is visible on shadows, not just certain shaders, and your radius has to be extremely high before this error occurs. Still, if the above solution doesn’t work, you may be able to narrow down the cause by playing with your light source. This may help you determine if the problem is indeed in the hair shader or rather something in the light itself.
