Two-sided SDF is generated when you import (or hit apply in the static mesh editor) and either you have enabled “force two-sided SDF” or your default materials in the static mesh are two-sided.
2 Likes
They changed the name (in a more positive way). This is becoming serious and mainstream!
1 Like
wdym? i haven’t touched the source in a couple weeks. out of space. it’s MEGAlights now? ohh well…
maybe change it to SSRTMLS - OIRTINAWUJSTADFS aka screenspace raytraced multilight shadows - or if raytracing is not available we use just screentraces and distance field shadows. 
1 Like
Honestly I’m just excited the tech is moving into experimental. It’s always surreal talking about experimental stuff such as this with other devs, and I forget that a lot of the stuff we experiment with isn’t even live yet. I like MegaLights as a name, it’s descriptive and fun at the same time. The main thing I’m excited by is just that we now have a lighting solution that can coherently handle basically anything you can render to screen, and theoretically hundreds of scene lights at once.
3 Likes
Is it something similar to the RTXDI where you can render hundreds of local lights without experiencing a performance hit?
In our archviz app, users can place lamps manually into the scene and there are many cases where there are many overlapping local lights which cause a big performance hit (think of big, open office rooms with lots of ceiling lights closely packed), would be great if this would provide a solution for such cases. Of course such rooms are easy to fake by combining many lights into a single one, but not all users have an technical understanding of it and it is not always possible with an archviz scene.
Basically, yes.
Longer version: it’s Epic’s version of RTXDI tuned for UE-specific use cases. The wrinkles in MegaLights are that it’s designed to handle local lighting while directional lighting remains its’ own thing, it’s more tuned for hundreds of lights than thousands, and it can use many different tracing methods (screen, DF, HWRT, etc) to scale across platforms.
3 Likes
What’s the connection between MegaLights and VSM? Can they be used together, directional lights VSM, other lights MegaLights?
Or VSM for Nanite heavy scenes and MegaLights for non-Nanite usecases?
MegaLights gets a lot of love according to the git commits and VSMs were never really that great IMO due to the reliance on Nanite. So are MegaLights the new cool shadowing technique?
That seems to be the idea, VSM for directional/hero lights and MegaLights for supporting. I read a bit on GitHub about how VSM/Megalights can now interact in some way, but I don’t know what I’m looking at so I won’t speculate.
Real time Path Tracing is finally coming to Unreal 5 using Restir!
But maybe only in the Nvidia branch:
Real-Time Path Tracing in Unreal Engine 5
October 1, 2024
4:15 PM-5:15 PMPT
Games
Room 431
This session will provide a demonstration of real-time path tracing in UE5 running on today’s hardware.
The demo makes use of ReSTIR importance sampling technology to achieve, for the first time ever, path-traced lighting in Unreal Engine.
Come join us to learn what you can do with real-time path tracing to achieve visuals that match the offline Path Tracer in UE5.
By Richard Cowgill
RTX Technology Evangelist
NVIDIA
4 Likes
Lumen GI makes material AO not work properly.
EDIT*
Material ao seems to work fine. the issue was more caused by the screen percentage with TSR… lsing detail and blurring it out…
1 Like
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?
2 Likes
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)
1 Like
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)
1 Like
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 :).
5 Likes
@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.
2 Likes
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! 
2 Likes