Bug with Substrate bsdf blends; when the transition is only one (or less) pixels wide, you get a black line on the transition

Development Rendering
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1

There’s a bug with Substrate bsdf blends; when the transition is only one (or less) pixels wide, you get a black line on the transition.

probably you are already aware as its mentioned in this thread

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Steps to Reproduce
The issue/repro steps are:

1. plug a mask that’s been clamped (so hard cut-off at 0 and/or 1 vs smooth transition) into the mix input of a horizontal substrate blend

2. you get these harsh transitions.

The only way to work around it currently is using asymptotic math, so that the blend mask values approach 0 & 1 but never reach them.

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3

Hi there,

Thanks for reaching out. Could you please send me the project you used to create that video? It’s so we can keep things consistent when recreating and fixing the bug.

Cheers,

Tim

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Hey Tim. Here’s the repo project, we managed to recreate the issue in a basic shader, so it’s super stripped down

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5

Hi Gregory, pardon my ignorance here, but which material parameter constant did you manipulate to get these harsh transitions? It seems the stripped-down version does not match the ones shown in the video.

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6

Hi!

That parameter isn’t present in the repro project, since it’s really and entirely different shader, made just to showcase the bug.

The issue should be visible as soon as you open the level, but here’s the parameter in the “MI_SubstrateHorizontalBlendBug” material instance that controls the transition being harsh or not:

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7

Ok, understood. Thanks for the clarification. I actually have some good news for you. I tested this project in our dev branch, and we seem to have fixed this issue (see screenshot). Are you looking to upgrade to 5.8, or do you need the fix right away? I can try to dig up the changelist in the latter case; otherwise, once you have migrated to 5.8, you should no longer have such a harsh transition in your Substrate materials.

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Hey Tim! Great to know it will be fixed in 5.8! We are okay with waiting for the upcoming release. Thank you very much!

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You are welcome! I will close out the ticket. If you still have problems with this issue after the upgrade, please feel free to contact us again.

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