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Maniphest T98641

Shader broken (unfortunately fixed?) after 3.2b, looking for a fix/workaround
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Description

System Information
Operating system:Win10 64b
Graphics card:NVIDIA RTX2060

Blender Version
Broken: blender-3.2.0-beta+v32.84e55e3dc251-windows.amd64-release; blender-3.2.0-candidate+v32.34f94a02f370-windows.amd64-release; blender-3.3.0-alpha+master.8589f60546b3-windows.amd64-release
Worked: blender-3.2.0-alpha+master.295d5c6ef5b9-windows.amd64-release ; blender-3.1.0-stable+v31.c77597cd0e15-windows.amd64-release

Short description of error
I've tried to import a shader I'm happy with (the one constructed in 3.2a) into a current project which is in 3.2b and it doesn't look the same:


Notice the shiny amazing lights on the left, may have been a happy buggy accident that got fixed in later versions (all of them, up to 3.3 alpha!!), but I wanted this effect. I attribute this difference to the Mix Shader node's Fac input somehow clamping/remapping its input.

So I'm looking for ways to reproduce this effect and to learn along the way of doing it.

I can port everything back to 3.2a/3.1st, but it's going to limit my geonode shenanigans and probably mess with other things.

And here's the full shader tree, made by following this Glass 2.0 guide by CG Vertex

Tried stacking "add shader" on top of each other, but I haven't figured it out yet, and I'm not very sure how can I utilize MixRGB.

I have a hunch that multiplication node is somehow pushing the RGB values past 1, which makes the surface emissive. But I can't figure out how to replicate the look and not lose other components of it - transmissiveness and caustics.

I tried looking for any relevant changelogs, but I haven't found anything that stands out to me that could be important.

Notice that I'm not using the upcoming native caustics feature.

Exact steps for others to reproduce the error
Here's the file. Run it in 3.1 stable, run it in 3.2beta (past the supplied version) and compare it back to back.

Related Objects

Event Timeline

Moooo (Cowbless) created this task.Jun 7 2022, 9:38 AM
Moooo (Cowbless) updated the task description. (Show Details)
Moooo (Cowbless) updated the task description. (Show Details)Jun 7 2022, 9:47 AM
Alaska (Alaska) closed this task as Archived.Jun 7 2022, 10:00 AM
Alaska (Alaska) added a subscriber: Alaska (Alaska).

The thing that is causing your glass/caustics to behave the way they did in older versions of Blender is a bug.
It was fixed in Blender 3.2 and as a result stopped your effect from working how you expected.

Since the behavior you want is a bug, we will not be rolling this change back and as such I am closing this report.

Moooo (Cowbless) added a comment.EditedJun 7 2022, 10:04 AM

Yeah well thanks, but can you at least do me the courtesy of pointing out the exact task number/changelog so I can figure out how to replicate this myself? If you say with confidence that it's a bug, there must be a task number/changelog that I can check out. @Alaska (Alaska)

Alaska (Alaska) added a comment.Jun 7 2022, 10:17 AM

I will bisect it for you and figure out what fixed this bug.

Moooo (Cowbless) added a comment.EditedJun 7 2022, 10:18 AM

Appreciate it. Because I can't find a workable solution with a shader tree. The buggy version simply returns more light than it should, but it is preserving the saturation somehow. While Add Shader doesn't, when you stack it it just turns everything white.

Also, searching this website for me is very unintuitive. I'll try again though.

Moooo (Cowbless) added a comment.EditedJun 7 2022, 10:34 AM

I believe I've found it. https://developer.blender.org/rB37300f330798ec7d2100d7bb2f2413813567aa53
I was trying to search by date, but you can't sort search by date here I think.

Now I'm off to research how to build my own version of blender with this fix unfixed.

Not 100% positive yet that this is it. It is unpublished.

P.S. I can't believe that this "issue", which not only is fixable with just a single clamp node, but also adds interesting possibilities, was actually considered a bug and squashed.

Alaska (Alaska) added a comment.EditedJun 7 2022, 10:38 AM

You're almost certainly right. That commit, or one like it, is probably the one that fixed the bug.

As for help with building your own version of Blender without the fix, I can provide you with some resources.
The Blender developers have a guide on how to build Blender here: https://wiki.blender.org/wiki/Building_Blender
To remove the the relevant change, just open the affected file and edit it to match the previous behavior. Then build Blender again.
https://blender.chat/channel/blender-builds is also some place useful you can go if you experience build errors.

Moooo (Cowbless) added a comment.Jun 7 2022, 10:43 AM

Thank you for these pointers! I'll restore the colorful justice!