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Alembic doesn't import vertex colors for meshes made of only vertices #109749

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opened 2023-07-05 16:21:12 +02:00 by mantissa · 8 comments
mantissa commented 2023-07-05 16:21:12 +02:00
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System Information
Operating system: Linux-5.15.0-76-generic-x86_64-with-glibc2.35 64 Bits, X11 UI
Graphics card: NVIDIA GeForce RTX 3090/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 525.125.06

Blender Version
Broken: Version: 3.6.0, branch: blender-v3.6-release, commit date: 2023-06-27 08:08, hash: c7fc78b81ecb
Worked: Never.

Short description of error
When importing Alembic caches, vertex colors are only imported correctly when the imported geometry is made of faces.
When the geometry is only vertices, no vertex colors are imported. (ex. point clouds)

I suspect this has to do with vertex colors encoded as a point attribute instead of a face corner attribute.
I've checked both provided alembic files in other software to make sure they're not the issue and they work fine everywhere else.

Exact steps for others to reproduce the error

  1. Import mesh.abc.
  2. Vertex colors are read correctly and are stored and accessible as a Face Corner attribute.
  3. Import points.abc.
  4. Vertex colors aren't read at all, expected behavior is that they're stored stored as a Vertex attribute.
**System Information** Operating system: Linux-5.15.0-76-generic-x86_64-with-glibc2.35 64 Bits, X11 UI Graphics card: NVIDIA GeForce RTX 3090/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 525.125.06 **Blender Version** Broken: Version: 3.6.0, branch: blender-v3.6-release, commit date: 2023-06-27 08:08, hash: `c7fc78b81ecb` Worked: Never. **Short description of error** When importing Alembic caches, vertex colors are only imported correctly when the imported geometry is made of faces. When the geometry is only vertices, no vertex colors are imported. (ex. point clouds) I suspect this has to do with vertex colors encoded as a point attribute instead of a face corner attribute. I've checked both provided alembic files in other software to make sure they're not the issue and they work fine everywhere else. **Exact steps for others to reproduce the error** 1. Import mesh.abc. 2. Vertex colors are read correctly and are stored and accessible as a Face Corner attribute. 3. Import `points.abc`. 4. Vertex colors aren't read at all, expected behavior is that they're stored stored as a Vertex attribute.
mesh.abc
3.1 MiB
points.abc
9.6 MiB
mantissa added the
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YimingWu changed title from Alembic doesn't import vertex type attribute vertex colors to Alembic doesn't import vertex colors for meshes made of only vertices 2023-07-06 05:41:03 +02:00
YimingWu commented 2023-07-06 06:08:28 +02:00
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Can confirm. Not sure if this a limitation of Blender or it's just a situation that alembic importer fails to handle.

@ideasman42 or @dr.sybren may want to take a look

Can confirm. Not sure if this a limitation of Blender or it's just a situation that alembic importer fails to handle. @ideasman42 or @dr.sybren may want to take a look
Pratik Borhade commented 2023-07-06 06:16:57 +02:00
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It seems alembic don't export attributes other than face-corner domain: #99293
Closing

It seems alembic don't export attributes other than face-corner domain: #99293 Closing
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Philipp Oeser commented 2023-07-06 10:16:39 +02:00
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Not sure why this was closed.

The referenced report is about export (and still open) and the closed report is about import?
Will check on this.

Not sure why this was closed. The referenced report is about export (and still open) and the closed report is about import? Will check on this.
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Philipp Oeser commented 2023-07-06 12:00:22 +02:00
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It is more of a TODO tbh, but will put on my desk

It is more of a TODO tbh, but will put on my desk
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Philipp Oeser self-assigned this 2023-07-06 12:00:31 +02:00
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Philipp Oeser commented 2023-07-06 13:44:43 +02:00
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Got it working, now needs a bit of cleanup and discussion in regards to

  • CD_PROP_BYTE_COLOR vs. CD_PROP_COLOR (atm. this is always CD_PROP_BYTE_COLOR and the data in the file looks like that as well, not sure if alembic can do differently as well?)
  • should importing be optional (as in the USD importer)?
  • once we are at it, exporting might be desired as well, not sure if there are any conventions in other apps as to how to handle this on the vertex domain? (the file from the report comes with kVaryingScope -- not kVertexScope -- atm. I only check the data size, if it is the same length as we have vertices, the attribute is created on the vertex domain...)
  • more come up along the way...

image

Got it working, now needs a bit of cleanup and discussion in regards to - `CD_PROP_BYTE_COLOR` vs. `CD_PROP_COLOR` (atm. this is always `CD_PROP_BYTE_COLOR` and the data in the file looks like that as well, not sure if alembic can do differently as well?) - should importing be optional (as in the USD importer)? - once we are at it, exporting might be desired as well, not sure if there are any conventions in other apps as to how to handle this on the vertex domain? (the file from the report comes with `kVaryingScope` -- not `kVertexScope` -- atm. I only check the data size, if it is the same length as we have vertices, the attribute is created on the vertex domain...) - more come up along the way... ![image](/attachments/73b3d952-9d70-45db-bd32-a3efb7a33e01)
image.png
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mantissa commented 2023-07-06 16:57:58 +02:00
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Thanks for looking in to this so quickly.

For reference, both alembics were exported from Houdini with default settings. I can have a look at the export options there if there's anything you'd like to know.

Thanks for looking in to this so quickly. For reference, both alembics were exported from Houdini with default settings. I can have a look at the export options there if there's anything you'd like to know.
Philipp Oeser commented 2023-07-12 12:35:42 +02:00
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OK, so apparently we have a much more generic solution in the works (at least for USD), see #109518, will try to coordinate this to have the alembic counterpart (not yet sure if alembic supports all of what USD does) coming along with the same features.

OK, so apparently we have a much more generic solution in the works (at least for USD), see https://projects.blender.org/blender/blender/pulls/109518, will try to coordinate this to have the alembic counterpart (not yet sure if alembic supports all of what USD does) coming along with the same features.
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Philipp Oeser commented 2023-09-26 12:59:14 +02:00
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Sorry, will step down to not block others on this matter (as I feel the way to go forward would be something more generic like #109518)

Sorry, will step down to not block others on this matter (as I feel the way to go forward would be something more generic like #109518)
Philipp Oeser removed their assignment 2023-09-26 12:59:22 +02:00
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