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Flipped polygons in Unreal

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I'm an Unreal developer working with a client who created a scene in Vectorworks. My task is to transfer it to Unreal so I used Datasmith. The process works as expected however I end up with meshes which are fully or partially inside-out. (See the attached image of a box.) The issue seems independent from export detail level. I'm using Unreal 4.26 and Vectorworks Spotlight 2021 SP3 1 (Build 588748) 64 bit.


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Yes, seems that VW never really cared about Face Normals for their geometry.


You can find flipped Normals especially in the more complex Plugin Object

created Geometry. Especially from Slabs, Stairs and, at least in the past,

even standard Extrudes had one Face flipped.


Usually that is a problem in any 3D Mesh based Software like Game Engines,

Modo, Blender (?), ....

But not in Cinema4D, which Cine Render Engine is also integrated in Modo.

So you will not notice sloppy Face Orientation.

The only reason is that C4D Renders every Material "2-sided" by default.

You will only notice Problems in C4D, if you manually deactivate 2-sided

or check for Face Orientation.


In Modo you would have to activate 2-sided for any Material instead,

as most times it may not be possible to repair all Meshes.

And even when 2-sided on, there can still be issues in advanced OpenGL

Viewports or visual problems for Global Illumination calculation.


The problems you mentioned for Datasmith were also seen in Twinmotion,

via Datasmith, which has 2-sided OFF by default too.

But if I got that right VW sends a 2-sided Tag for any Material when exporting.

Could just be that this does not work in any case for Datasmith export,

which seem to be still in WIP.

I am sure there will be more fixes in Datasmith Export for VW SP4 but

don't know when it will be released.


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Oh, by default 2 sided materials were created but they just covered up the core problem... with inside-out meshes, lightmapping will produce unusable results, that's why I need to fix the meshes somehow... I hoped for an automated way because manual labor is both slow and expensive.

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We tag Datasmith materials as two-sided, Twinmotion and Unreal Editor use those tags to show correct shading.


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Posted (edited)
15 minutes ago, ZoltanE said:

Oh, by default 2 sided materials were created but they just covered up the core problem... with inside-out meshes, lightmapping will produce unusable results,




I also think that 2-sided hammer ist just a workaround and does not

really help at all in some situations.


That is why I would prefer clean geometry from VW.

I postulate that since nearly a decade, but it does not seem to share

development's highest priorities.


I don't know if you have access to C4D, Modo, .... where first one has

really good options to clean up meshes, and export to UE from there.

Otherwise you could just export a FBX into Blender, which repair options

are AFAIK not bad either.

Edited by zoomer
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Oh well I guess I will set up the workflow for manual cleanup. Thank you for the help Zoomer!

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