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This is rather interesting, Missing Material Slots, where did they dissapear to?

Exported a mesh out of Unreal Engine (my ship pilot’s mesh). He has 19 material slots, exported him as a static mesh to load to Mixamo online rigger, after rigging then loaded his rig back into Blender, added in the missing root bone, exported back into Unreal Engine, Imported into Unreal Engine and lo behold, his eyes I can’t texture them but as I move the camera closer in his head I find
as the camera clips into the eyeball, the eye texture is only texturing inside of his eyeball not on the outside (I check the material and its checked double sided), I look down at the material slots, to find out why I can’t texture the outside of his eyeball and find he only imported in only 10 of the material slots from Blender!!

Anyone else finding Unreal Engine is not importing in all the material slots from Blender?

Make sure that you have a material in each slot or you won’t get a material slot in UE4, and also make sure that the polygons are facing the correct direction.
I also highly recommend that you reduce the number of materials, 19 and even 10 materials is too many and will impact performance.

Goodness. So if there’s any blank material slot in Blender, then UE4 won’t interpret it as a material slot.? Or are you talking about any slots in Blender that have got ‘world grid material’ in them?
(shows up in blender as light grey ball in the materials tab…) Sounds like I have to re-assign
the material slots again in blender and then export, and then those slots should show up in ue4.

Looking down at the LODO section in UE4 under the materials tab I can see the slots that UE4 has chosen. and the eye material slot is definitely not there.

polygons facing the correct direction?
Can you explain a little about this? and how to correct it if this is a Blender issue?

If you have an empty material slot in Blender then it will not show up in UE4. I’m not familiar with how Blender works since I use 3ds Max, but in Max I can apply a multi-material to an object and in that I can change how many slots I want, but if one of those slots doesn’t have a material in it then it won’t be there in UE4.

As for polygons facing a direction–in 3D software polygons always have a facing direction, typically by default you will not see anything on the backside which helps make rendering faster. Each vertex actually has a direction it’s facing as well (the vertex Normals) which is used to determine things like how a surface is smoothed. In 3ds Max if a polygon is facing the wrong direction I can just select it and press Flip and it’ll turn the opposite direction.

Well, I suspect Blender assigns a world grid material if there’s no material assigned, or if it can’t find the material. But Unreal may Interpret that as a blank slot. I don’t know if Blender has multi tier slots or not. So do you think the polygons on the eye have somehow been
flipped by Blender? (is that what you mean by wrong direction?) Or why is UE4 texturing
all inside the eye ball and not texturing all outside it?

The other possible conclusion I come to is that Blender somehow made a double overlap copy of the eyeball which unreal can’t detect a material slot for so its texturing the eyeball inside the overlap copy, but not texturing the extra eyeball that’s covering it making it look like its only texturing the inside
of the eye and not the outside…

Could be a bug in Blender that’s been set off somehow, no matter I can export and try again and see if it repeats it.