Hi,
No idea and hard to guess what is happening without more details or a repro unfortunately.
Hello,
It is hard to guess what is going on without more details. The conversion node is needed because we need to support all the previous legacy shading models. It should not generate those errors but we will check packaged build for 5.4.
Thanks for reporting.
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Ah, I see. Thank you for taking the time to explain it to a more or less shading novice, much appreciated. Assuming by medium scattering you mean something other than a MFP variable, would something like a volume texture bound to the domain of the material surface facilitate different material consistencies through the medium of the slab?
Anyways, very excited to be a part of exploring the technology, it feels absolutely revolutionary coming from a real-time background.
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The scattering resulting from the medium itself would be dependent on MFP and DiffuseAlbedo. Having a volume texture to simulate volumetric material details, if that is what you meant, is currently not supported in Substrate (but it is somewhere in the long list of things to try and experiment with).
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Hello,
I am trying to convert a material from a project using legacy shading to use substrate. I’m trying to understand why there is a visual difference between the two, if it is a bug or just an edge case that works differently now. The material is for a misty smoke particle vfx.
Often in vfx when we have billboarded particles, in order to prevent the particle from appearing as if it’s lighting is changing as we walk around it, we use this trick and just force the material normals to be a specific value (in this case worldspace (0,0,1) ). Previously, this worked great, but now using substrate (both the auto-generated conversion, and a slab set up from scratch) there is this odd lighting artifact or something on the material.
First image is legacy rendering. Note how the billboard quad is all a solid color. This is how it should work.
Second image is with substrate enabled. Note how there is now a horizontal line across the quad. That is somehow related to the light direction?
If I change the value in the roughness input, the artifact does visually change, but does not disappear. This makes me believe that is artifact is related to the specular term or is environment reflections or something, even though specular is 0, does that not disable reflections entirely?
Lumen is disabled in the examples but it happens with lumen also. Testing in a fresh project in the basic map. Auto exposure is off, set to manual (11). Bloom and directional light shaft occlusion is all disabled. This is also visible in a scene with nothing but a quad and directional light, but is a bit more subtle. Quad is just a bp with a material billboard.
Is this a technique that just isn’t possible anymore with substrate? Or is there a more correct way to setup the substrate material that I am just doing incorrectly? Happy to supply any extra info if needed.
Thanks!
@SebHillaire There is some serious visual bug with materials rendering, attempting to understand why:
When one shifts the mode of the skylight from stationary to static or movable or however, textures in the scene randomly shift around from mesh to mesh, and it’s a different permeutation every time it happens. It resets upon the mesh being moved, and the lumen surface cache lacks coverage in the bad meshes. PT and hit lighting reflections both don’t notice the difference.
I have added this on the list of things to look at for us.
This could be due to the rough diffuse solution we have. Try setting roughness to 0 see if it improves.
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We have a fix for that one. We are looking at having that in a next 5.3 patch. Thanks for your patience. In the meantime, if anyone wants to get the fix early, please integrate this change.
Do note that this is not a bug related to substrate in any way, so please next time I would kindly ask you to create a separate thread.
As a reminder: this thread is dedicated to feedback about Substrate. For instance: its workflow, parameterization, shading results, performance, avenue for research and improvements. If a problem you are looking at reproduces with substrate OFF, then it should not be posted in this thread.
I understand this is tempting, but we need to remain focused. Thank you all for understanding. We really value your feedback, enthusiasm and all the discussions here around Substrate! 
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Thanks! Yeah, bringing roughness down to 0 does smooth it out a bit it, but there is still some weirdness. Even with specular set to 0, when roughness is 0 we do get the sun specular showing up. (which I would have assumed specular to 0 would have prevented that, as we don’t want a reflective specular surface!). But primarily, there still a horizontal line across the material, just less sharp now but still noticeably there.
Super thanks for sharing, worked good. Im having some sort of issue with overly green areas, like metallic, but thats something else in my shader probably.
That is very very fair. Especially considering the state that the lumen thread has descended into, being proactive about keeping things on topic is a very good move.
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Hey, guys I need help.
I’m trying to use translucent substrate material.
RectLight does not work on reflections from translucent materials.
The metal substrate material works well with RectLight.
The translucent substrate shows RectLight reflections with path tracing enabled.
Could it be a bug or configuration error?
My engine version is 5.3.
SubstrateGlassPathTracing (RectLight Work)
SubstrateGlassRaster (RectLight Not Work)
SubstrateMatallicRaster (RectLight Work)
The EmissiveColor input on the Volumetric-Fog-Cloud BSDF does not seem to do anything. Bug? Been using this in a few projects to better art direct the look of clouds a bit.
@BjornCogxgoc Thanks, I have added that as a bug to our list.
@DMeville I suppose you are talking about 5.3: good news, this has been fixed and will be in 5.4.
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@SebHillaire Thank you so mutch! 
Area light do not work in forward with Substrate enabled or not. That is in fact a performance choice.
I’ll add an item to discuss with the team here if we can enable that if explicitly chosen by an artist on a material or per project.
EDIT: this is already possible to enable using r.RectLightAtlas.Translucent 1. (project setting, need to restart the editor to recompile translucent shaders). I exposed the cvar on the project settings window for better discoverability.
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We are pushing soon a rewrite on how Substrate works with Lumen on UE5 main. If it is similar to the issues we saw in the past, it should fix it. But to be sure, would you be able to share a small repro project to check there is no other side effect we are missing?
Thank you
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@SebHillaire thanks.
I used cvar and had no success in Substrate with AreaLight.
So I disabled Substrate in another test project to see if the translucent material worked with AreaLight. To my delight it worked.
But I ended up discovering two other bugs in Unreal Engine 5.3.1
First bug
Translucent material does not appear in reflection.
I’m using Lumen
Second bug
When I enable PathTracing the translucent material appears in the reflection, but the floor with reflection always has these stripes
Translucent materials do not appear in Lumen as of today (with Substrateor not). This is the current state. Please report lumen issues in the Lumen thread.
If I understood correctly, those issues are from a project with Substrate OFF. Please remember that this is a thread for Substrate only. See my comment from Substrate - Feedback Thread - #194 by SebHillaire
If I missunderstood and it is with Substrate, then remember that the path tracer is not up to date with Substrate.
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Hi, is a way to disable it without launching Unreal? I can’t open my project now.