Armature with bone using Axis Angle or Euler rotation modes not importing properly with FBX


(Shaderbytes) #1

Hi there Sketchfab Devs

I was trying to import a skinned mesh where just one of the bones is using a different rotation mode , the default for all other bones is Quaternion wxyz , I tried both Euler xyz and Axis angle for this one bone , it works perfectly in Blender, I can also reimport that FBX into a new file and it works as expected.

In sketchfab this bone does not rotate properly , it is supposed to spin around its y axis only .. but instead it gets all wobbly on the other axis' as well.

Now what is strange is that I can use the blender addon to upload the model and it imports as it should ( well 99.9% perfect , small bit of imprecision but I could get around that problem )

Im not sure if you are aware of this issue , I can provide the fbx files for testing or the blend file etc..


(Waleguene) #2

Hi @shaderbytes,

I would be interested by both FBX and BLEND file, it will be easier for us to investigate :slight_smile:
About the interpolation issue, it's a feature we added in FBX but not yet un Blender. Animation is baked at a fixed frame rate and such quick transition are not correctly handled. I made a ticket on our side to handle this.


(Shaderbytes) #3

Ok cool ,I will upload then to google drive just now and send you the link.

(Shaderbytes) #4

I sent you a PM with link to the files on google drive. The bone to observe is "dot_lights" , there are two blender files and fbx files. One set is for Euler mode and one set is for Axis angle. Only the dot_lights bone has this mode applied.

chat soon

(Waleguene) #5

Thanks @shaderbytes,

Here is what I get:

Is it the issue you mentionned ? (a slight rotation around x/z axes that make dots entering in the geometry)
It's a compression issue that we can't really fix for now. A workaround would be to add a very small offset to the dot_lights geometries to avoid having them fighting with the object and make the bug less visible

Sorry for that :confused:

Rotation Animation Looks Weird
(Shaderbytes) #6

Yes , this is the error , but your suggestion is not a feasible based on how bad the error is at its worst, Here is a screenshot I just did in the model inspector. As mentioned before it wobbles but at the worst part of the wobble this is ~13 deg if viewed from the side. To compensate that would mean moving the lights way to high above the surface. They would not appear to be on the surface at all when not animating.

You didn't mention why it is so bad with fbx import only? Why when using the blender exporter does this import with much much less imprecision? I would think errors from compression are the small bit of clipping seen when using blender exporter. ( which I mentioned was manageable by doing a small offset ) but the fbx error must be something else.. its just too big an error. unless you are using two different compression techniques , one worse than the other?