In UnityGLTF/PBRGraph, Specular options (IOR, 0..1 value, Color, Map, Enable flag) doesn't work at all

[XtroTheArctic]

Describe the bug 💬

In UnityGLTF/PBRGraph, Specular options (Index of Refraction, Specular value, Color value, Specular Map, Enable/Disable flag) doesn't work at all. I didn't test other options like Specular UV and Specular Color but I wouldn't expect them to work either.

I marked a zone in the roof section of my specular texture as full black. In Blender, the model is correctly rendered without a specular effect in the roof section.

In Unity (via UnityGLTF), the model is rendered with a default specular effect no matter what while ignoring any change made on specular related values in the material. Assigning/removing "specular map", even disabling "Enable Specular" make no change at all.

Steps to reproduce 🔢

1. Download the zip file and extract it.
2. Import GLB file to Unity project (or Export it first using the Blender file).
3. Compare the visual differences on the model between Unity and Blender (as described above)
4. Extract the material in GLTF importer's materials tab and manually modify the extracted material in Unity.
5. See that UnityGLTF shader ignores all specular related values including enable/disable flag.

Files to reproduce the issue ♻

BakeryBuilding.zip

Editor Version 🎲

Other (Provide details below)

Render Pipeline and version

URP 16.0.4

UnityGLTF Version

2.16.1

Operating System 👩‍💻

Windows

When does this problem happen?

• Editor Import
• Runtime Import
• Editor Export
• Runtime Export

Additional Info 📜

Unity: 2023.2.2
Blender: 4.4.3

Validations 🩹

• I have searched existing issues: no issue already exist that reports the same problem.
• I follow the Code of Conduct
• I provided a minimal reproducible example, including files when necessary.

[hybridherbst]

Hey, this is unfortunately a known issue with Shader Graph in URP – you can try it yourself: using the specular option and then plugging in data in a new empty graph will not work in all cases. If you happen to have a good explanation or know how to reliably fix that we're all ears :)

There are a few other material properties in PBRGraph that have data but no visuals – e.g. anisotropy and clearcoat – which helps with correctly roundtripping material data but is of course not ideal. We should probably add some UI hints that the those pieces of data will not have a visual effect in those cases.

[XtroTheArctic]

Hmm. You say this is an official Unity bug, you say? Interesting and sad. I have little experience with Shader Graph and I can try to repro what you describe but if you guys are not able to find a solution, I have no chance doing so :) I'll let you know if I get lucky. Thank you very much.

[XtroTheArctic]

I did some research and hands on experience. It turns out not to be a Unity bug but a design choice on their end.

Shader Graph has 2 modes: Metallic and Specular. Metallic mode disables the Specular Block and the Shader Graph developer isn't able to change any specular behaviour at all.

From my research, I found 2 possible solutions:

1. Recreating the shader starting from an Unlit shader graph and implementing entire lighting system to make it look like a lit shader.
2. Not using shader graph and writing the shader via code.

Both of these options wouldn't be viable for UnityGLTF developer, I presume. Am I right?

[XtroTheArctic]

Why does IOR not work thou?

As far as I can see in UnityGLTF/PBRGraph, it's used in Volume calculation which connects to Base Color and Alpha blocks in Fragment node.

[XtroTheArctic]

Sorry, one more question.

Why is roughness and metallic maps are implemented as a single property instead of 2 separate maps?

Shouldn't it be possible to make a portion of a material fully rough while not being metallic like a rock or sand?

[XtroTheArctic]

Sorry, one more question.

Why is roughness and metallic maps are implemented as a single property instead of 2 separate maps?

Shouldn't it be possible to make a portion of a material fully rough while not being metallic like a rock or sand?

Answering my own question. It looks like you guys get roughness-metallic texture as 2 channels and use those channels for final metallic and roughness values.

[XtroTheArctic]

I resolved my specular related problem by creating a roughness texture (inverse of specular texture) and using it instead of the specular texture. Now I understand that, I don't need a specular texture while using a metallic shader workflow.

One last outstanding issue is this then:

Why does IOR value in UnityGLTF shader not work?

As far as I can tell, it's not related to specular block of fragment node.

Can you consider this as a bug?

[robertdorn83]

hey,
have you setup the Rough Refraction render feature? Otherwise, IOR would not work.

[XtroTheArctic]

No, I didn't. I didn't know such requirement. Since my first priority was converting my FBX models to GLTF, I haven't seen the material configuration part of the readme documentation. I'm sorry. Thank you for telling me.

Although, now that I added it to my renderer, I still see no effect of different IOR values on the material. Hmm. I must be missing something else.

---

Hmm, I found what was missing. I think the implementation of UnityGLTF shader considers IOR as being a transparency property.

Readme documentation mentions enabling Transmission and Volume (optional). When I enable Transmission and increase its value, I still don't see any effect on the material while changing the IOR value. Enabling Volume finally starts to show the IOR effect on the material... BUT...

I was expecting IOR to work similar to what I see in Blender. I am not expert on these graphical stuff but, as far as I can observe in blender, IOR is not only related to the transparency of the object. It affects the base color of the material and specular strength even for non-transparent materials.

Is this kind of IOR behaviour out of scope for UnityGLTF?

[XtroTheArctic]

Hello. I hate to bother you but, it's been a long time while I was busy with animation related stuff. Can I kindly ask if you please see my question in the comment above? Thanks in advance.

[XtroTheArctic]

My PRs can wait more, no problem there but can you guys please check my question above?

[XtroTheArctic]

@hybridherbst Can you check my question above when you have some free time please?