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FBX import from Blender has "degenerate tangent bases" and is shaded incorrectly

I imported a simple TV stand into UE4 from Blender and I got this error message: alt text

I looked under the object's LOD0 details in the Edit Object panel and it already has "Recompute Tangents" checked. I don't know if the tangents are resolved or anything, but my mesh is exhibiting some very strange shading behavior and I get the uncanny feeling that the two errors are related. alt text

I circled the areas where the strange shading is located - the handles have been inverted! They are shown as protruding inwards rather than outwards, as they do in the original file. (The Blender preview is on the left, UE4 with sample textures on the right)

My TV stand ALSO does weird things with glass - and I've been searching all day for a resolution to this problem, only to find out that BSPs exhibit this but FBX imports shouldn't. The glass material lets you see through the table all the way to the floor and wall, even though you wouldn't be able to see through it if the glass wasn't there! Again, it might have something to do with the shading bugs. alt text

What can I do to fix these problems? I've tried rebuilding my lighting, importing the objects as one mesh, and texturing differently. I also already have basic, albeit crappy, UV maps set up. They don't make much of a difference. Any help would be appreciated.

Product Version: UE 4.7
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asked May 21 '15 at 11:40 PM in Rendering

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Yules
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Hi Yules,

Degenerate Tangents are not a bug. While the message could be more clear to explain what's going on, this is really just a UV that needs to be setup properly.

This post goes into a little more detail to explain what this is and how to fix it:

https://answers.unrealengine.com/questions/119361/degenerate-tangent-bases.html

Thank you!

Tim

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answered May 22 '15 at 01:44 PM

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Tim Hobson ♦♦ STAFF
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avatar image Yules May 22 '15 at 03:38 PM

Thank you for the link, I will read up on degenerate tangents!

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