Any way to render reflections behind translucent glass surfaces like in modern games with ray tracing, and also how to get proper refraction, without ugly mess on screen, I tried both way to render with Translucency set to Raster I can’t use refraction and don’t have reflections behind glass, with Translucency set to RayTraced I get slightly better refractions, and reflections on other surfaces when looking through the glass, but in reflections I have no lights and shadows, and other translucent surfaces is completely opaque, so both ways are a complete mess only option are left is PathTracing, but it’s not an option, how to resolve this, glass surfaces are a most common thing in any scene for now UE5 is useless, I will put some screenshots later
Here are the settings, all turned up to the max.
After three months of research, The only thing I want to ask is…
And how to fix it? Because I know it’s possible, we’ve seen it in many games with full RT and also with PT
Translucency shouldn’t be set to raytraced when using Lumen as it doesn’t support any of Lumens features, so you won’t get GI or indirect shadows in reflections. Also pretty sure it is deprecated and Epic is not fixing any of the problems with it so…
When using rasterized translucency you can’t use realistic IOR values for materials, it behaves as though the “ray” never exits the medium and so it it will be bent way more than it should. Rasterized refraction is a screenspace effect so if the rays go off screen you’ll just get a hard edge and then the refraction effect just vanishes, if they hit a foreground object then the foreground object will show up in the refraction.
If you ask me IOR should have never been added as an option since you effectively can’t use any real IOR value with rasterized translucency, which is the only translucency method worth using. But I don’t make the engine so…
Raytraced refraction for Lumen is still a WIP as far as I know, in theory it should solve these issues and there’s a check box in project settings for it but it doesn’t appear to do anything for me in 5.5. Others have experimented more with it in the Lumen feedback thread so you can likely find more info on how to get it working there. I say, “in theory” because there are still likely to be limitations with it, particularly when it comes to Nanite meshes.
This is just an inherent limitation of Lumen’s reflections, only the first layer of translucency can have high quality reflections.
The TL;DR version is: Translucency in Unreal is a mess, it has quite a lot of feature conflicts that are not well described. To some extent this is unavoidable, due to the way all the features work. You’re not going to get glass rendering that matches the path tracer in every context.
the raytracing scene is currently solid. you cannot trace thru objects, unless they have a masked texture. refraction is limited to screenspace. i dunno if and how raytraced refraction works, currently. it’s been limited in the past too, tho.
also… translucent objects don’t exist in the raytracing scene they are composited later. hence why you cannot raytrace glass to see it reflect glass. glass will reflect a mirror once. but a solid mirror can not reflect a translucent glass surface.
you can however use dithered glass to get a decent semi translucent look at 50% opacity, that supports multiple bounces. or atleast looks like multiple. it turns into a solid mirror after the first bounce. no refraction obviously, cause it’s basicly solid pixels, temporaly stabilised. and the other issue with that is, it’s highly unstable due to dithering. neither does it cast proper shadows. the dithering doesn’t align with light vectors to get a correct pattern. i tried that a couple times and failed. so… w/e
The problem I have in my scene is that I have two layers of glass and curtains. You can see them on the right. I can’t properly render anything with them, so I use a “wannabe glass” material and completely opaque curtains instead.
What bugs me the most about it is that yesterday I played Spider-Man 2, which has all sorts of ray-traced reflections and refraction, and it runs at 120 FPS on my PC.
