With fbx: quads turn into tris


(Klaasnienhuis) #1

When uploading an fbx of a model exported from within 3dsMax, Sketchfab turns all polygons into triangles. I've confirmed the fbx exports actually contain quads. There's a "triangulate" export setting in the fbx export settings in 3dsMax. It's turned off for these tests. When I upload the same model as an obj, quads are retained.

I'd expect the geometry being kept as is.

Model URL: https://skfb.ly/KzBB, https://skfb.ly/KzCu

How to stop tris from appearing in viewport?

When I open the original FBX in other software, I see tris.

FBX Review:


(Klaasnienhuis) #3

I'm not sure about Maya, but fbx review gives me tris no matter what. It seems to me it triangulates the model no matter how it's exported. It also triangulates the quad obj's which look good on sketchfab. So fbx review appears unsuitable to review triangulation.

Anyway, I've tested a bit and noticed something. All tests have been done with 3dsMax 2016 and fbx 2016. I'm testing the "triangulate" option in the fbx export options, nothing else. I've tested by uploading the model to sketchfab and turning on the wireframe. Using fbx review was of no use me, since it shows triangles at all times. The testmodel was a single editable poly with one quad (4 vertices)

  • Turning the "triangulate" option on produces models with triangles. That makes sense.
  • Turning "triangulate" off also produces a model with triangles, which is unexpected.
  • Turning "triangulate" off AND setting the fbx output to ASCII gives me quads!

When I compare two ascii exports with triangulate on and off in notepad I can clearly see the extra edge in the "triangulate=on" model. I'm unable to compare the binary files but their bytecount is exactly the same while the ascii versions are not.

But then I quickly tested two binary fbx exports with triangulate=off with the fbx 2014/2015 and fbx 2013 versions. Both versions show quads in sketchfab.

Conclusion: the fbx 2016 exporter appears to ignore the triangulate settings OR there's a difference how you import fbx between 2016 and other versions.

Here are the exports in all the different versions I've used: fbx test exports.zip (19.8 KB)


Hmm interesting results.

It's not clear to me if it's a problem with 3ds Max or the 2016 FBX SDK.

@waleguene could you take a look?

(Klaasnienhuis) #5

@james, @waleguene,
Any info on this? If it's a problem with 3dsMax and how it exports the 2016 fbx version I probably can revert to fbx 2015/2014. If it's a problem you can solve with the fbx sdk then I can leave it to you.

"Frame per second" export FBX error
(Waleguene) #6

Hi @klaasnienhuis,

What was the mode of your object when you made your exports?

I made some tests on my side and it seems that it depends on the mode of the object in 3dsMax. I tested exports of a cube in 3 different mods (Primitive/Poly/Mesh) and got triangles for Mesh in both ASCII and binary samples, and Quads for Primitive and Poly exports.

When I import your 2016 samples in 3dsMax, for the ASCII sample I get the plane in "Editable Poly" mode, and for the binary one I get it in "Editable Mesh" mode. I would suspect a change between the two exports, but I don't know a lot about how 3dsMax imports FBX and set modes so I may have missed something.

Could you give another check to validate this ?

Here are my tests: FBX_exports.zip (29.7 KB)

(Klaasnienhuis) #7

Apparently I've made a mistake. I've tested with primitives, poly and mesh objects. Probably somewhere in my script these were all converted to mesh. And meshes show up as triangles.
I've found the part of the script where this happens and modified it. And now I'm able to publish quads with the fbx 2016 version.
I guess I was blaming max for my own mistake... Thanks for checking it out though.