The emissive Material seems to be very expensive.
Is there a way, to still use an emissive material (to visualize the glow effect) but somehow exclude it from the Lumen GI calculation?
Instead, I would just use a simple light source.
Seems to be cleaner and much cheaper.
Lumen still picks up pixels from the screen, so really you canât (this is a problem theyâve mentioned). Though, looking at the video in this post, it looks like it can be excluded from the lumen scene, but it still gets picked up by the screen.
However, you may able to âfakeâ emissive through a post process applied before tone mapping; just mask the emissive parts and set their color value to something bright. I donât have UE5 installed right now, so I canât test it.
Also, I thought emissive materials had no additional cost?
the emissive feature in Lumen is def problematic in a practical sense. the smaller the emitting object is, the more noisy the gi around it gets. Sure turn up gi quality and the noise goes away but then u lose perf. if you have a flashing emissive material. lumen is too slow to update so it ends up looking swimmy. not to mention that other than obj size and emissive amount/color, there is no control over fall off.
its possible Epic is working to improve some of this
Yes it works fine for me. Make sure your inputs have the same name as the custom code and that youâre passing different values into each input. One input will output to the rastered image and the other will output to the lumen scene.
Your material setup looks fine - What you are seeing there is the screen trace. This is why it achieves the desired result on the faces that arenât visible to the camera, but not on those that are in screen space. I didnât notice it in my use case before but in a new test I do see it. It can be removed with the command:
r.Lumen.ScreenProbeGather.ScreenTraces 0
Changing this will probably have some other visual or performance implications.
Screen Trace On:
A user in another thread discovered you can achieve a similar result by unchecking the box âAffect Dynamic Indirect Lightingâ in the mesh details panel without needing the custom node. Not sure if there are other differences between the methods (besides applying at the per mesh level instead of per pixel level), but it still leaves the screen trace visible so just like before it seems that needs to be disabled to get the desired result in most cases.
I canât really point you in a specific direction with your comment because it most definitely works and my last postâs photo proves as much (in 5.0.2 at least). Try this checkbox, or double check your material and then either way disable screen traces.
Itâs a bit hacky so I expect it could introduce some other issues elsewhere though, so hopefully itâs addressed in another way later.
This might be one of these dirty Hacks, but i just discovered that setting the Blend Mode of a Emissive Material to Translucent (Opacity can stay at â1â aka default) makes Lumen completely ignore the emissive & reflective Part of the Material ⌠might be exactly what you guys & girls are looking for
Now that would be a migrane and a half. Is that even optically possible irl? Can something glow and be translucent, or would that be some kind of blackbody problem?
Wait, given that glow sticks are a thing I believe I answered my own question. Still, to have something simultaneously emit light, receive GI, sort, and shadow correctly would probably be pushing the bounds of whatâs even conceivable in real time. Iâll wait for 5.2 to introduce it
Thank you for all of your research on the issue @BananableOffense, knowing that the r.Lumen.ScreenProbeGather.ScreenTraces is creating the additional light in the scene even if the mesh is not in the lumen scene is really helpful.
As you said, having a per material solution to solve this without having to deactivate the traces for the whole scene would probably be the best way to solve this.
I couldnât agree more with this comment. If this is easily possible (it might not be) this would be a massive add to Lumen (especially for non-physical rendering looks). For increased credibility, I would have killed for this when I worked at Riot as an art director.
In the recent Fortnite focused tech blog something stuck out to me:
âSome problems were easier to solve. Lumen uses screen traces to add detail where software ray tracing is lacking, but grass is so detailed that these screen traces were introducing significant aliasing. A simple workaround to skip screen trace hits on foliage was enough to solve the artifacts.â
This seems to suggest it is indeed possible to skip scene traces for only certain elements.
Perhaps @Daniel_Wright could enlighten us on if this is something we can easily apply elsewhere when screen traces are unwanted?