Incorrect parent tree when exporting and importing scene with multiple rigged objects #56677

New Issue

Campbell Suter · 2018-09-04T07:04:20+02:00

Campbell Suter commented

2018-09-04 07:04:20 +02:00

System Information
Arch GNU+Linux, Kernel 4.18.5

Blender Version
Broken: 2.79.6, Git 19c65cd (branch master)
Worked: None that I'm aware of

Short description of error

If you have a scene with multiple rigged objects, the armatures and meshes are incorrectly parented upon exporting then importing them. Rather than there being two armatures at the root of the scene with each one containing a single mesh, there will be (if you have two objects) one armature at the root, the other armature as a child of it, with both meshes attached to the inner-most armature.

Note that this certainly seems to be a fault of the importer and not the exporter: I've manually reviewed the exported model and it appears fine. Additionally, upon attempting to import a Collada file generated by custom software I've got the exact same problem as importing the file generated by Blender.

Exact steps for others to reproduce the error

Start with an empty scene, and create a cube. Add a single bone. Make the cube a child of the bone, using the armature deform with automatic weights option (not using any weights prevents this problem from occurring).

Repeat this a second time.

Export the scene as a Collada file.

Open a new instance of Blender, and import the scene with Collada.

The objects will have incorrect parents, and this has consistently occurred each time I have tried it:

Here are the screenshots of the scene, before exporting (matches attached blend file):

And after export/import:

Sample Blender file before export: expimptest.blend

**System Information** Arch GNU+Linux, Kernel 4.18.5 **Blender Version** Broken: 2.79.6, Git 19c65cd (branch master) Worked: None that I'm aware of **Short description of error** If you have a scene with multiple rigged objects, the armatures and meshes are incorrectly parented upon exporting then importing them. Rather than there being two armatures at the root of the scene with each one containing a single mesh, there will be (if you have two objects) one armature at the root, the other armature as a child of it, with both meshes attached to the inner-most armature. Note that this certainly seems to be a fault of the importer and not the exporter: I've manually reviewed the exported model and it appears fine. Additionally, upon attempting to import a Collada file generated by custom software I've got the exact same problem as importing the file generated by Blender. **Exact steps for others to reproduce the error** Start with an empty scene, and create a cube. Add a single bone. Make the cube a child of the bone, using the armature deform with automatic weights option (not using any weights prevents this problem from occurring). Repeat this a second time. Export the scene as a Collada file. Open a new instance of Blender, and import the scene with Collada. The objects will have incorrect parents, and this has consistently occurred each time I have tried it: Here are the screenshots of the scene, before exporting (matches attached blend file): ![Screenshot_20180904_165511.png](https://archive.blender.org/developer/F4549446/Screenshot_20180904_165511.png) And after export/import: ![Screenshot_20180904_165717.png](https://archive.blender.org/developer/F4549475/Screenshot_20180904_165717.png) Sample Blender file before export: [expimptest.blend](https://archive.blender.org/developer/F4549308/expimptest.blend)

Campbell Suter commented

2018-09-04 07:04:20 +02:00

Added subscriber: @ZNix

Gaia Clary was assigned by Bastien Montagne

2018-09-04 09:19:28 +02:00

Gaia Clary was unassigned by Dalai Felinto

2019-12-23 16:36:00 +01:00

Dalai Felinto commented

2019-12-23 16:36:00 +01:00

Added subscriber: @GaiaClary

Aaron Carlisle commented

2020-02-15 22:40:46 +01:00

Added subscriber: @Blendify

Aaron Carlisle commented

2020-02-15 22:40:46 +01:00

I can confirm

Cordell Bloor commented

2020-06-10 17:06:49 +02:00

Added subscriber: @cgbloor

Cordell Bloor commented

2020-06-10 17:46:19 +02:00

I noticed there's a comment in the ArmatureImporter that says:

This is not safe when we have more than one armatures in the import.

A bit of printf debugging reveals that unsafe path is taken when importing a COLLADA file exported from Campbell's expimptest.blend. Perhaps that's related. I don't understand the code, but commenting out that if block results in each armature being given its own child armature (so, 4 armatures when importing 2), but the armatures in the COLLADA file do become seperate, top-level armatures.

I noticed there's [a comment in the ArmatureImporter ](https://developer.blender.org/diffusion/B/browse/master/source/blender/io/collada/ArmatureImporter.cpp;v2.83$617) that says: > This is not safe when we have more than one armatures in the import. A bit of printf debugging reveals that unsafe path is taken when importing a COLLADA file exported from Campbell's expimptest.blend. Perhaps that's related. I don't understand the code, but commenting out that if block results in each armature being given its own child armature (so, 4 armatures when importing 2), but the armatures in the COLLADA file do become seperate, top-level armatures.

Cordell Bloor commented

2020-06-10 21:38:09 +02:00

So, I think more or less understand the problem, though solving it is another matter. In the COLLADA file itself, the root joint node points to the instance controller, which has a skin that points to the geometry. The OpenCOLLADA Sax parser, however, has a different structure, and it's not super clear how you go from a COLLADAFWSkinController, COLLADAFWSkinControllerData or COLLADAFWMesh to the COLLADAFWNode (or vice versa).

Blender creates its armatures when it encounters the armature nodes and needs to add data to them when it encounters the skin controllers, but it's not really clear which node the skin controller is for. So, the author of the importer just picked the first one and put a TODO to fix it for files containing multiple armatures.

So, I think more or less understand the problem, though solving it is another matter. In the COLLADA file itself, the root joint node points to the instance controller, which has a skin that points to the geometry. The OpenCOLLADA Sax parser, however, has a different structure, and it's not super clear how you go from a COLLADAFWSkinController, COLLADAFWSkinControllerData or COLLADAFWMesh to the COLLADAFWNode (or vice versa). Blender creates its armatures when it encounters the armature nodes and needs to add data to them when it encounters the skin controllers, but it's not really clear which node the skin controller is for. So, the author of the importer just picked the first one and put a TODO to fix it for files containing multiple armatures.

Gaia Clary commented

2020-06-10 21:53:50 +02:00

I would say this is more of a missing feature than a bug. I actually tried to solve this issue a while back (some years ago) but at that time i was not able to fix that. I guess the original developer skipped that for a reason ... And i am also not sure if this is a nice to have feature or a must fix issue.

Opinions are welcome :)

I would say this is more of a missing feature than a bug. I actually tried to solve this issue a while back (some years ago) but at that time i was not able to fix that. I guess the original developer skipped that for a reason ... And i am also not sure if this is a nice to have feature or a must fix issue. Opinions are welcome :)

Cordell Bloor commented

2020-06-10 22:50:23 +02:00

For me, it's just nice-to-have. I can concaternate all my objects together, or script importing a series of files, and it will be almost as good.

One thing that would have helped me is a warning in the log or console when trying to import a file with multiple armatures. I spent a while thinking I had screwed something up in writing my COLLADA file. A message from the importer would have saved a bunch of debugging.

For me, it's just nice-to-have. I can concaternate all my objects together, or script importing a series of files, and it will be almost as good. One thing that would have helped me is a warning in the log or console when trying to import a file with multiple armatures. I spent a while thinking I had screwed something up in writing my COLLADA file. A message from the importer would have saved a bunch of debugging.

Gaia Clary self-assigned this 2020-06-10 23:06:43 +02:00

Gaia Clary commented

2020-06-10 23:06:43 +02:00

This is a valid complaint :)
I add a warning.

This is a valid complaint :) I add a warning.

Philipp Oeser removed the

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Incorrect parent tree when exporting and importing scene with multiple rigged objects #56677