New OBJ exporter no longer groups faces by material, causing issues with some other apps (e.g. Procreate)

Kuzey commented

2022-03-16 04:01:45 +01:00

Blender Version
Broken: version: 3.2.0 Alpha, branch: master, commit date: 2022-03-14 19:06, hash: fc259d4c30
Worked: I tried it with Blender 2.93.0 2021-04-19

Short description of error
When exporting obj from blender 3.2 with multiple materials assigned breaks object in some other apps (e.g. Procreate on iPad).

The issue seems to be that the new exporter does not group faces by material, whereas the old exporter did.

Exact steps for others to reproduce the error
Load the monkey model

add subdivision surface modifier and set to level 3

apply modifier

in edit mode assign different materials to the object ( at least 3)

export obj (try all settings and or combinations there of)

import into procreate

see video of the new obj vs old obj exporter

objexport.mov

**Blender Version** Broken: version: 3.2.0 Alpha, branch: master, commit date: 2022-03-14 19:06, hash: `fc259d4c30` Worked: I tried it with Blender 2.93.0 2021-04-19 **Short description of error** When exporting obj from blender 3.2 with multiple materials assigned breaks object in some other apps (e.g. Procreate on iPad). The issue *seems* to be that the new exporter does not group faces by material, whereas the old exporter did. **Exact steps for others to reproduce the error** Load the monkey model add subdivision surface modifier and set to level 3 apply modifier in edit mode assign different materials to the object ( at least 3) export obj (try all settings and or combinations there of) import into procreate see video of the new obj vs old obj exporter [objexport.mov](https://archive.blender.org/developer/F12929358/objexport.mov)

Kuzey commented

2022-03-16 04:01:45 +01:00

Author

Added subscriber: @kuzey

Pratik Borhade commented

2022-03-16 06:39:50 +01:00

Member

Added subscriber: @PratikPB2123

Pratik Borhade commented

2022-03-16 06:59:58 +01:00

Member

Changed status from 'Needs Triage' to: 'Needs User Info'

Pratik Borhade commented

2022-03-16 06:59:58 +01:00

Member

I can not reproduce when importing same file back to Blender.
Does this only happen when importing obj file in Procreate?

I think Procreate is only available for ipad, right?
#96511.blend

I can not reproduce when importing same file back to Blender. Does this only happen when importing obj file in Procreate? I think Procreate is only available for ipad, right? [#96511.blend](https://archive.blender.org/developer/F12929654/T96511.blend)

Kuzey commented

2022-03-16 07:22:26 +01:00

Author

Yes ipad only.

Yeah the object seems normal in blender, it's a bit strange.

what if you exported the obj from 2.9 and 3.2 and compare the files, would that narrow things down?

Thanks

Yes ipad only. Yeah the object seems normal in blender, it's a bit strange. what if you exported the obj from 2.9 and 3.2 and compare the files, would that narrow things down? Thanks

Pratik Borhade commented

2022-03-16 07:58:53 +01:00

Member

Hi, I exported in .obj format from 2.93 & 3.2 then imported back to respective versions and I don't see any difference after comparing them.

Aras Pranckevicius commented

2022-03-16 08:15:47 +01:00

Member

Added subscriber: @aras_p

Pratik Borhade commented

2022-03-16 09:37:12 +01:00

Member

Changed status from 'Needs User Info' to: 'Needs Triage'

Kuzey commented

2022-03-16 12:30:24 +01:00

Author

Without access to procreate it would be difficult to test I guess.

I exported the obj from both versions of blender and opened them up in sublime text and saw something interesting.

Could it be the formatting and or the order of lines that's causing the issue?

in the old version (highlighted) the text is:

'usemtl Material.001
s off'

in the new version (highlighted) the text is:

's 0
usemtl Material.001'

Maybe it's the change from text to binary (line 's off' to 's0') that is the problem or the fact that in the new version, 's0' is above "usemtl Material.001" ?

It could explain why there is no issue importing it back into blender, maybe, I'm just guessing :)

Without access to procreate it would be difficult to test I guess. I exported the obj from both versions of blender and opened them up in sublime text and saw something interesting. Could it be the formatting and or the order of lines that's causing the issue? in the old version (highlighted) the text is: 'usemtl Material.001 s off' in the new version (highlighted) the text is: 's 0 usemtl Material.001' Maybe it's the change from text to binary (line 's off' to 's0') that is the problem or the fact that in the new version, 's0' is above "usemtl Material.001" ? It could explain why there is no issue importing it back into blender, maybe, I'm just guessing :) ![oldobj.jpg](https://archive.blender.org/developer/F12930001/oldobj.jpg) ![newobj.jpg](https://archive.blender.org/developer/F12930002/newobj.jpg)

Aras Pranckevicius commented

2022-03-16 14:41:06 +01:00

Member

@kuzey I can't reproduce the issue here in Procreate. Export monkey models with multiple materials with blender 3.0 & 3.1, and yes the .obj content is slightly different like you mention above, but importing both into Procreate on iPad, everything seems to work fine.

Could you attach your "works fine" and "is broken" .obj files to the bug report?

@kuzey I can't reproduce the issue here in Procreate. Export monkey models with multiple materials with blender 3.0 & 3.1, and yes the .obj content is slightly different like you mention above, but importing both into Procreate on iPad, everything seems to work fine. Could you attach your "works fine" and "is broken" .obj files to the bug report?

Pratik Borhade commented

2022-03-16 14:49:17 +01:00

Member

Changed status from 'Needs Triage' to: 'Needs User Info'

Kuzey commented

2022-03-16 15:22:06 +01:00

Author

I redid them, I'll include 3 files:

worksfine.obj is from 2.93.0

broken.obj is from 3.2

broken2.obj is the same as the previous one, but I selected a random square patch on the left side of the head and assigned that to one of the existing materials. This one is the most broken, it has many more layers in procreate.

Hope they help

broken2.obj

broken.obj

worksfine.obj

I redid them, I'll include 3 files: worksfine.obj is from 2.93.0 broken.obj is from 3.2 broken2.obj is the same as the previous one, but I selected a random square patch on the left side of the head and assigned that to one of the existing materials. This one is the most broken, it has many more layers in procreate. Hope they help [broken2.obj](https://archive.blender.org/developer/F12930213/broken2.obj) [broken.obj](https://archive.blender.org/developer/F12930214/broken.obj) [worksfine.obj](https://archive.blender.org/developer/F12930216/worksfine.obj)

Scurest commented

2022-03-16 20:17:59 +01:00

Contributor

Added subscriber: @scurest

Scurest commented

2022-03-16 20:17:59 +01:00

Contributor

The old exporter groups all faces with one material under a single usemtl line. The new exporter doesn't and switches back and forth between materials many times.

Perhaps Procreate treats each usemtl line as the start of a different "material slot", while Blender treats all usemtl M lines (with the same M) as reusing the same material slot.

I'll attach a ZIP with two .obj files of a three-material Cube that differ only in this aspect. If BrokenCube.obj is broken and WorkingCube.obj works, then you'll know this is the reason.

TestCubes.zip

The old exporter groups all faces with one material under a single `usemtl` line. The new exporter doesn't and switches back and forth between materials many times. Perhaps Procreate treats each `usemtl` line as the start of a different "material slot", while Blender treats all `usemtl M` lines (with the same M) as reusing the same material slot. I'll attach a ZIP with two .obj files of a three-material Cube that differ only in this aspect. If BrokenCube.obj is broken and WorkingCube.obj works, then you'll know this is the reason. [TestCubes.zip](https://archive.blender.org/developer/F12930511/TestCubes.zip)

Kuzey commented

2022-03-17 06:27:35 +01:00

Author

So the question is, which is the current industry standard?

The old way or has it changed and is Blender just using the newest convention?

I think I might report this as a bug with Procreate as well, just to be on the safe side.

If this is indeed the industry standard, would it be wise to bring back the old exporter and call it legacy for a few months or so?

Update: I Just sent a bug report to Procreate

So the question is, which is the current industry standard? The old way or has it changed and is Blender just using the newest convention? I think I might report this as a bug with Procreate as well, just to be on the safe side. If this is indeed the industry standard, would it be wise to bring back the old exporter and call it legacy for a few months or so? Update: I Just sent a bug report to Procreate

Aras Pranckevicius commented

2022-03-17 08:52:06 +01:00

Member

I can see an issue with the monkey repro files in Procreate, but I can't quite validate that theory with the simpler "TestCubes" case. It's as if, yes, the fact that 3.1+ obj exporter does not "group" faces by material is creating some issue for Procreate, but it's not as simple as "each usemtl group ends up creating it's own subset". Looks like the Procreate logic in obj importing is "something else".

That said, I think the best course of action would be to fix 3.1+ OBJ exporter to group faces by material again. Who knows how much other random software is out there that implicitly assumes that faces are grouped. I'll try to make that fix.

I can see an issue with the monkey repro files in Procreate, but I can't quite validate that theory with the simpler "TestCubes" case. It's as if, yes, the fact that 3.1+ obj exporter does not "group" faces by material is creating *some* issue for Procreate, but it's not as simple as "each usemtl group ends up creating it's own subset". Looks like the Procreate logic in obj importing is "something else". That said, I think the best course of action would be to fix 3.1+ OBJ exporter to group faces by material again. Who knows how much other random software is out there that implicitly assumes that faces are grouped. I'll try to make that fix.

Aras Pranckevicius self-assigned this 2022-03-17 08:52:47 +01:00

Aras Pranckevicius commented

2022-03-17 08:52:47 +01:00

Member

Changed status from 'Needs User Info' to: 'Confirmed'

Aras Pranckevicius changed title from ~~new Obj exporter messes up if object has multiple materials assigned~~ to New OBJ exporter no longer groups faces by material, causing issues with some other apps (e.g. Procreate)

2022-03-17 08:54:24 +01:00

Kuzey commented

2022-03-17 11:23:48 +01:00

Author

I gave the link to this thread in my Procreate bug report, hopefully it'll be useful for them going forward.

Thanks everyone and cheers :)

I gave the link to this thread in my Procreate bug report, hopefully it'll be useful for them going forward. Thanks everyone and cheers :)