Sketchfab is separating the edges of animated models?

Hi there,

I’m working on a animated model and I noticed I’m getting “holes” and “cuts” on it when uploading to Sketchfab. I’ve tested it with FBX and Blender files.

Here’s an example of a previous model where the same issue can be noticed. If you zoom in on the edges, you’ll notice lots of them are separated, which is not the case in the original model.

On the current model I’m working on, the “cuts” are much more visible, it’s literally breaking the model.


I wonder if this is some Weight Painting approximation issue or something like that. What can be done to fix or avoid this kind of problem?

Thank you! :slight_smile:

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Hi there,

I just reprocessed your cactus using different processing settings (no compression of vertex coordinates). Can you check if the result has improved?

I can do the same for your new panda model, but it will revert to default settings on each re-upload.

Hi James, thanks! It did!

Is there anything I can do on my front that prevents this? The panda model is not final yet.

Thank you!

Our vertex compression is known to be somewhat problematic for morph animations. I don’t think there’s much you can do on your end ( @waleguene - any advice? ), but I’m happy to reprocess it for you without compression once you’re ready to publish. Just let me know.

Hi @murilo_kleine,

I suspect that some vertex splitting is involved in the processing.
In Blender, vertex attribs (Normal/UVs etc) are by polygon, not by vertices.
On Sketchfab, everyting is bound on vertices, so when a same vertex is used by different faces with different vertex attribs, we need to duplicate it, and this duplication might create holes in the model.

It seems to be a bug, and I don’t think that using a different compression setting would help
I’m making a ticket to check this, but unfortunately I cannot give any ETA for the fix

Update: I just saw that it was an FBX and not a .blend file. Did you try to weld all vertices ?

Thank you, James!

Hi Waleguene, thank you, that’s great news! :slight_smile:

The vertices are all welded, there’s no edge crease or anything, it’s a single “solid” model, as was the Cactus. The FBX file seems to be working alright from what I tested, it happens only when uploaded to Sketchfab.

I quick check the FBX and I don’t get why it looks broken on both Sketchfab and FBX Review. Looking weird on the latter makes me think that it’s caused by the loading (some subsurface or tesselation issues).

It seems to work better when uploading directly the .blend file, but still some weird shapes:

I get the same broken result as FBX when exporting to glTF and loading it in, but reimporting the FBX to Blender works.

I don’t have any workaround for now, the only diff that could explain the results is that Blender doesn’t use the FBX SDK for it’s imports/exports, but the other tools do.

I’m opening a ticket for this, but I’m afraid it will not be in the road map for the incoming weeks :confused:

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Thanks Waleguene!

I’ve seen similar problems before that were related to the weight paint of the models (bone affecting vertex/face deformation threshold), maybe there’s some incompatibility between Blender and Sketchfab solutions for weight paint value/resolution?

I know that Blender’s values range from 0 to 1000, including any rational/fraction number in between … maybe Sketchfab uses a simplified method or scale down resolution as it does to image textures? I dunno, but by the mesh deformation seen on the image you sent it does remind of that :slight_smile:

Thanks anyway!

I uploaded a new draft with normalized weight painting (meaning the highest value of the highest vertex of each bone group is now set to 1000) making it more evenly distributed. It seems to have solved the holes in the model, but it is still deforming the mesh in the wrong way.

Hi all,
I am far from being a Blender or FBX pro, but have you tried exporting from Blender using the Alembic format for animations? Worked great for me some months ago (Blender 2.79). Hope this helps

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I did some tests and managed to replicate the exact same problem in Blender. It happens when I lower the amount of bones that can affect a vertex.

Based on my tests, it seems Sketchfab only allows for 4 bones simultaneously affecting an specific vertex. Blender has a higher limit by default.

I’m not sure if that’s by design or not, but at least now we know what’s happening and I can fix it on my front :slight_smile:


Hm, that’s a very good point actually, I forgot to check on this side.
We are using this limit in the processing as well , since it doesn’t really make sense to have more for real time rendering.

(We are planning to improve logs/warnings coming from processing, and that’s one info that is worth adding)

Thanks a lot

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Hi, I’m also getting holes in my model, as well as deformation errors (particularly visible between the pants and the belly). Can you “reprocess” this as well?

Or is using alembic my best bet? That would increases the file size almost 10 times, so I was hoping to avoid it.

Thank you

EDIT: Alembic is out of the question - The file size increases about 100 times, not 10(!)
Uploading an alembic version isn’t possible.

Hi @Theon, in my case, the Alembic file is just about the same size as the Blender file if not smaller. I was using 2.79 but I don’t think it should be different with 2.8.

It probably depends on the animation setup, rig and length of animation. Mine became impossibly large when baked to alembic.

Yes probably, my animations are short (100 frames). One thing I noticed is that you have to export only selected objects, especially if you have several layers with unused objects.
In my case I often had to close and reopen Blender before exporting otherwise the Alembic file was huge. Don’t know why. Now with 2.8 I don’t know how this is working
Good luck