Import FBX from Blender

Hello folks,
I have a problem importing an FBX mesh from Blender. If I export it to Blender in the normal way (normal, scale, an UV are correct), then I have “holes” at the corners. But if I export the whole thing via Datasmith, these are not available.

I am using UE4 version 4.26.2 and Blender 2.93.1.
Maybe someone here knows this problem and could help me.


It looks a bit like it’s no unwrapped correctly. Can you show the UV map in UE?

Could just be that somehow the normals are flipped.

I can’t say I fully understand the first post tbh…

That kindof looks like degenerate geometry being culled out.

Degenerate triangles are when the faces are too small for UE to handle them well. If you get an error when importing about x object has degenerate triangles, that would be the problem. It is usually an issue with scale. Since blender is set to meters as its default scale instead of centimeters things frequently come in too small. Changing blender units to centimeters and unit scale to 0.01, checking to make sure the object is the correct size and then applying scale in blender should help. (you will frequently have to scale up by a factor of 100)
Datasmith rinses models before import, so that might ignore this issue.

I wrote a plugin for this

And there is one through epic games as well:

Both are free
My use cases are for film specifically but should translate into the games sphere as well.

If the model was just indented there’s no way that blender has created degenerate geometry.

It usually preserves square (4 vert) faces unless you manually triangulate and reduce the geometry.

You could argue the engine is causing degenerates when triangulating.

In that case it’s sufficient to triangulate before export (add a triangulation modifier and apply experimental on export) to avoid having the engine cull out things in the process.

That said, if these import fine at 10cm size, then there’s no way a 1m cube could ever be experiencing any issue.

Thanks all for your answers!
But unfortunately I haven’t been able to solve the problem yet…

I actually use the “Send to Unreal” plugin. There is no error message in Unreal. The size fits. the curves are very small, about 2mm. These are my export settings from the plugin:

this could actually have something to do with the degenerate geometry. but if I select Triangulate before exporting and apply experimental in the plugin, then it is unchanged.

but if I set the scaling up, the curves are beautifully formed. But then it’s just too big. :sweat_smile:
I checked the normals in Blender with the option “Face orientation”. They are OK (all blue on the outside). :+1:

I think if it is due to the UV maps, then it should at least be displayed correctly in the wireframe view in Unreal? :thinking:

here is the Blender file.
Handle.blend (14.8 MB)

If you really need a super small extra detail object don’t use geometry but bake a normal map.

You won’t really see the difference in engine anyway.

Edit: I found a way!

When I open the mesh in Unreal, deactivate the “Remove Degenerates” option in the “Details Panel” and re-import the mesh, the “holes” disappear. Of course it would be nice if it would work automatically, but it works for me.

Thank you all!

I just popped open your model @Jonny_le
Those corners are going to cause degenerate triangels in ue by default, the surface area of each face in them is too small.

There are a few solutions to this:
If you need the detail because a camera gets incredibly close to the object, scale up by 10x in blender, import into UE, and then when you place the object in the scene scale by 0.1 (this is definitely a hacked solution)
If your whole world is designed that small, you might want to consider scaling up everything by 10 or 100%. It will mess with how light falloff works a bit, but is a frequent trick when dealing with small scales.
Probably the best solution is modeling the corners with 1 level less of bevel would probably do it. Maybe 2 less. Unless you are getting very close to the object you will not notice a difference since from a short distance away your triangles become smaller than the size of a pixel. So any extra detail gets crunched out. The image below shows the difference in appearance (higher object is 3 levels of bevel and set to shade smooth in blender)

Otherwise, your normals look good, as does any issues with triangulation.