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Inverted normals only in pathtracer

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Ghogiel greentooth

Im doing an archvis marketing project.

Parts of this office chair I made simply won't render in pathtracer without some faces being inverted.

Modeled in max, baked in marmoset, textured in substance. Here it is with and without textures in the scene in both raytraced and path tracer



Looks fine in Max, marmset, substance, etc

This is the geo

UV of borked section

What I've done:

exported as obj and reimported the geo and then rexported from max to engine to see if that cleared anything

Tried different combinations of turn to poly and the fbx exporter to export both tri and quad versions and seen if imported any variation of it would resolve when imported into UE.

cleared all the vertex channels.

Tried a bunch of combos of weighted normals and clearing and resetting normals.

Tried importing just the seat back into Maya and exporting from there

Tried a ton of combos of import settings in UE. Import normals/weighted normals etc.

Tried just importing the chair back and for whatever reason that specific geometry is still borked.

chair back obj if anyone wanted to see if it's borked on their end.


The one thing that fixes it is finding the affected faces and manually retriangulating those specific faces the other opposite direction. So it's solvable to some degree in max by hunting down and turning invisible edges until they render correctly (and rebaking to the new triagulation layout). But there is nothing special about the triangulation going in either direction imo, so some sort of Unreal pathtracer rendering bug?

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