I see dark "lines" around edges of imported models from Blender

Unity Engine
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1

This is the model in Blender and it’s pretty smooth with Shade Auto Smooth option applied:

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I export it as FBX for Unity:

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But in Unity, you see dark lines on the mesh, and they seem around the quads edges. So I guess it is a smoothing related issue:

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I tried to change option in imported model’s Import Settings in the Unity inspector, like changing normal to calculate and other options, but they didn’t get rid of this issue.

I personally want to do smoothing only in Blender. But it doesn’t seem to working. It’s nothing complex model.

Could anyone let me know what’s wrong here?

2

What modifiers do you have on the model in Blender?

3

Only Auto Smooth but I applied it before exporting.

4

It looks like the top half of the model is smooth-shaded, but not the lower half. Have you tried manually smoothing the faces? i.e. select the faces and then [object->shade smooth] in edit mode?

5

I’m not sure it’s smoothing related now. If I rotate those objects 180 degress on their center (like earth), the issue doesn’t change the direction, it’s still on same direction.

Manual smoothing in Unity itself made no difference.

Which made me think it’s lights and shadow related. So while troubleshooting, I found this “Depth” and “Normal” bias options under Directional Light options in inspector. I increased depth a little and for some reason it got rid of that. Don’t know why and how though.

6

This might be caused by Screen Space Ambient Occlusion (SSAO), which is enabled by default in URP and is often the cause for weird or unwanted shading effects. I noticed that these kinds of artifacts appear when in the SSAO Renderer Feature (in the URP Renderer asset), “Source” is set to “Depth Normals”. When set to “Depth”, it looks fine. However, this only seems to happen in one of my URP projects I only use for testing stuff, but not in others. So it’s likely that the actual cause is something else.

7

It isn’t related to SSAO in my case. You may want to see my previous comment to see what seems to have fixed the issue.

8

Shadowmaps store discrete distances from the light, as a result, each texel in the shadowmap is either fully shadowed or not. The problem with this is that a surface may cast shadows on itself, leading to what it’s known as “shadow acne“ which is what your problem was.

The depth and normal bias options under Directional Light options offset the distances in the shadowmap to make sure it reports surfaces as being at a distance larger than zero from themselves, getting rid of shadow acne/self shadowing. If you use bias values that are too large, you’ll get the opposite artifact - objects whose shadows don’t seem to touch the ground, making them look as if they were floating above it. This is called “peter panning“.