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Objects are black after building lighting, it's not an issue with Lightmap

Hi all,

I have imported this building into UE4 which is made out of multiple objects (wall, windows, etc). There are 2 of these items that render black and I have no idea why.
They are perfectly unwrapped on both UV channel 0 and 1, the light map resolution is also high enough as well (1024).

I even when back to 3Ds Max, reset Xform, and bring it back, still the same thing.

All other objects that have been imported work completly fine, it’s just a couple of them not working fine.

Also, if it makes any difference, the building was made in a BIM software such revit or CAD (i’m not the one who designed it), then imported in 3Ds Max then into unreal.

Also, I’ve tried setting the object as moveable as well, still no luck.

Any ideas what could be causing this?

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Found the solution actually, the normals were wrong in 3Ds Max.

But I did have 2 sided textures and double sided geometry checked, not sure why it still didn’t work with those options ticked. Only worked once I fixed the normals in 3Ds Max.

Any Ideas?!

In game engines geometry is always one sided (unless the engine basically duplicates the mesh), due to optimizations and how GPUs work. If the normal is inverted, it’s receiving lighting from the other side of the mesh, if it’s 2 sided and inverted, each side is still receiving lighting from the opposite side of the mesh.

It’s fairly common for CAD, sketch up, or other programs not intended for games to have tons of issues games wont like, including inverted or meshed up normals, ngons, unwelded verts, etc.