I saw this update to github and was immediately excited by it- the wording is a little confusing to me, but does this mean that lumen now supports caustics? And if it only applies to lumen reflections, does that mean indirect lighting supports caustics when direct shadows do not?
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Likely, but I would read that as something more-accurate for how substrate works. All things transmit light, just more or less. Ice, water, fog, glass could all be examples.
So ‘yes’ but I wouldn’t think for water-specifically.
Hi Everyone,
I’m facing a very weird bug that I’ve never seen before with Lumen Surface Caches.
Basically my whole Lumen scene cache is marked as Missing surface Cache but those surface caches will pop in and out of existence at certain distances from the camera, having this kind of flickering effect. I’ve been working a lot on this bug and though it would be interesting to know if you guys have any input.
I’m using UE 5.4, Nanite (And nanite displacement on most of my scene). I tried to disable nanite but it doesn’t change anything. It looks like something is corrupting the computation of which object surface cache should be streamed and discarding surface caches that should be shown.
When I duplicate an object that has Missing Surface cache on the viewer and Isolate it somewhere spatially, then the surface cache appears again without issue. Is there a cap on amount of Surface caches/mesh visible for lumen on the screen ? It looks like when their is too many object it starts to discard random one in a panic.
Did someone encountered something similar and was able to fix it ?
Thanks
Could you pull up the visualization of the mesh cards themselves? I’ve never seen a bug quite like this before, but I’m curious if there might be an issue with the way the cards themselves are being projected.
Bug in UE 5.5 preview: enabling hit lighting for reflections creates blocky noise in lumen scene and surface cache. (default content examples project, HWRT)
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Hit lighting for lumen reflections is broken on Packed Level Actors (HISMs?) with Lightmapped GI in 5.5EA1
Selected wall is a PLA of rescaled default cubes, they show up with soft gradient lighting in reflections. The wall on the right and the ceiling visible in the reflection are just regular static meshes, they are reflecting correctly (they’re also just rescaled default cubes)
(Screen traces are disabled for this screenshot to better illustrate the problem)
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Where should we put feedback for Megalights?
I’ll create a thread after we’re back from the Unreal Fest. There are also some last minute MegaLights changes to merge into 5.5 and some docs to write :).
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@Krzysztof.N Anything regarding glitches in one eye in vr in combination with MegaLights on the list of changes ? If not, will make a testcase to easily reproduce it.
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Wowsy, smooth metals with 5.5 preview now looking good, even at distance:
Previously (from 5.0 to 5.4.4) Lumen reflections were blurry as hell with smooth enough metals, but now they looks so much better! Thanks for improvement! 
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But what do they look like without Temporal AA/SS?
They looks same without AA, but temporal component (that you personally don’t like at all) now involved in to Lumen reflections themselves it seems - reflections gradually goes from blurry to sharp in a second when camera stops moving. Very nice improvement over default blurriness.
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I’ve seen those artifacts on Vulkan, but everything seems to be running fine on DX12 with my 4080. Are you running with DX12? Which GPU it is?
It’s DX12, 4070 . i7 9700k intel 10th gen. Substrate disabled, MegaLights disabled.
tried a driver update? nvidia and unreal had some compatibility issue the last couple weeks. mhhhmm
also… interesting you still rocking a 9700k. 8 threads are nice, but even the ps5 has more to offer if it’s pushed to the limit. tbf… the editor and engine is not that cpu hungry. mostly gpu.
back in the lab. i never noticed lumen does full hit light bounces on characters. or is that new? i think i was too focused on the world shading. about those mirrors tho… and now being able to use baked gi.
how high are the chances to get a shader combo that does realtime gi in the main trace and uses the worldspace lightmap volume for static in reflection gi on characters? not necessarily the full lightmaps. just a basic volume sample and diffuse term to light up the dark shadows on characters. i’m aware this shot is screentrace territory but if i would turn up the camera to upper torso it would fall apart in the reflection.
also noticed the surface cache noise in reflections has gone down a good bit in this test shot. which is good. reflection hit skylight 1 is still a secret option too - for color artists that’d rather juggle and blend the gi ambience and skylight. nice.
CPU upgrades are on the list but not really needed, I haven’t been bottlenecked by it in anything but games for a while. Besides, if I really need the power I can OC it a lot and get it for most things.
I’m definitely loving the new hit lighting GI. For most game scenes it doesn’t make a difference, but anytime there’s complex or dense geometry, it can be transformational. Obviously costs an arm and a leg, but the shading difference now between lumen and PT for anything opaque is very, very small. I haven’t tested out the new translucency behavior, but I’m kind of amazed at how little the visual difference is in most scenes.
Plus, MegaLights is just superb. I’m having to squint to notice the tiny differences in noise between standard RT and megalights, and it can handle so many more lights (although I don’t particularly understand the debug viewmodes atm).
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I am sorry @Krzysztof.N , I confused and I gave you my desktop specs when I got that screenshot on my laptop: that screenshot was taken from a Framework 16 laptop, which has a Ryzen™ 7 7840HS, and a AMD Radeon™ RX 7700S mobile GPU with 8GB VRAM. Everything else I said was true, HWRT, surface cache, no MegaLights. Error does not seem repeated on my desktop.
In addition, viewmode performance is extremely bad- about a third of what lit mode is.
In addition, SSR is completely broken in 5.5 preview- when lumen is enabled, all reflections disappear with no fallback.
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That sounds great. To have some visual/rendering improvements.
Do we have some comparisons somewhere ? I read the UE 5.5 Roadmap but I could not find anything about “hit lighting GI”.
Here’s a very artificial case to really illustrate this.
This is a material which outputs the camera vector as RGB. Screen traces are off to make it even more obvious.
Exhibit A: Surface cache:
Because the surface cache is rendering cards, the view vector of the card is baked into them. This would cause a material reliant upon this kind of effect to look wrong in it’s card. Fresnel is another example of this.
Exhibit B: Hit lighting for reflections
Here, the only difference is in the shiny gap/ grout line between the tiles. With reflective hit lighting, it is now correctly picking up the true camera direction vector in reflections.
Exhibit C: Hit lighting for reflections and GI
Now the light being emitted from the bottom and backside of the mesh are also red because they are properly evaluating the cameras view direction instead of the view direction the card was baked from.
If lots of geometry in a scene has an inaccurate surface cache representation for reasons like this, the GI of a scene, especially in cases where screen traces fail, can be totally wrong.
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