Hello,
We’re looking at the possibility of using raytracing & hit lighting to support perfect mirrors in our title (there’ll be some additional custom work on our side to support this - but the issue mentioned here is reproducable in vanilla 5.6), however there’s a few issues which can prevent us from doing so.
Looking at the LumenScene radiance probes, some of them (depending on the geometry they are placed around) are completely black. Modifying the “LumenRadiosityHardwareRaytracing” shader to write “1” to the output radiance doesn’t seem to fix the issue (as a quick test), they are simply not updated. I think what’s happening is they are either getting ignored from the probe update or culled in a previous pass. Screen traces have been disabled on purpose.
This results in significantly darker and non-uniform reflections, especially around skeletal characters (see repro project and screenshots).
The issue mentioned is reproduced with the default settings (apart from enabling raytracing and hit lighting for reflections in the settings).
Thank you
Pantelis Lekakis
Firesprite - Lead Programmer
Steps to Reproduce
Open supplied sample project.
- Start PIE and eject the camera so you can see the character and/or the spheres in the level.
- Visualise probes via “r.LumenScene.Radiosity.VisualizeProbes 1” and “r.LumenScene.Radiosity.VisualizeProbeRadius 2”
- Disable screen traces via “r.Lumen.Reflections.ScreenTraces 0” so they don’t mask the reflection result.
- Notice that especially around the character, most probes are black, contributing to a significantly dark reflection
Noticeable on the perfect mirror floor material which I have supplied ( see screenshots ).
Raytracing should be already enabled in the project settings.
Hi there,
I’m sorry for not getting back to you sooner. We have been on a break, and I am just now getting around to this issue. Since the radiance probes are being traced from a set tile region in the surface cache (4x4 by default), hitting an invalid texel that stores invalid data in the radiance probe is possible. As a result, you will see a darkening of the surface geometry near these invalid radiance probes. We recently managed to push out some fixes for this issue, but they did not make it into 5.6. You can integrate them into your build to see if this helps your issue. The CLs can be found in UE5-Main CL 42807500 and 42840128. Alternatively, you can try increasing r.LumenScene.Radiosity.ProbeSpacing will tweak how the probes are placed on the surface, although this will likely not be as good a solution as integrating the CLs. Please let me know if you have any further questions.
You are welcome! Let me know if this ends up helping you or if you need further assistance
You are welcome! I’m glad to hear that the changes are improving your output. If you run into further issues with your Lumen setup, please feel free to reach out again. I will close out the ticket for now.
Hi Tim,
Thank you for chasing this and I will be looking at integrating the CLs, as reducing the probe spacing is not good enough and hurts our performance quite a lot (tried it last week).
Let me get back to you once this is integrated.
We have integrated this in our 5.5 stream (with some changes cherry-picked from our 5.6 upgrade one) and it seems to work fine, the results are indeed better.
I noticed some changes to threadgroup sizes which hopefully I copied over correctly. I have double checked with my colleague and we’re confident it’s right, afaik only the integration is a 2d dispatch.
Hopefully we won’t have any more problems!
Thank you very much