alembic attributes doesn't respect alembic standard #88275

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william eguienta · 2021-05-14T07:03:27+02:00

william eguienta commented

2021-05-14 07:03:27 +02:00

System Information
Operating system: All
Graphics card: Nvidia RTX 2080Ti (x8)

Blender Version
Broken: 2.92.0 Master

Short description of error
blender export of custom properties is not right

other DDCs reports a trigger by non-scalar properties in the .userProperties of an object, so for instance in the example /Cube.userProperties.static_int which is an ArrayProperty.
this makes data unreadable or can crash some others DCCs
ex : what maya can see
the userProperties can only be written on transform level, but the alembic standard is to do it on shape level. (don't look at maya for this, maya does it wrong too by default )
we should be able to choose if properties are at xform or shape level and default must be on shape normally

Exact steps for others to reproduce the error
add custom attributes on objects
export alembic with custom attributes on
inspect the alembic with abcls
custom-properties.blend custom-properties.abc

**System Information** Operating system: All Graphics card: Nvidia RTX 2080Ti (x8) **Blender Version** Broken: 2.92.0 Master **Short description of error** blender export of custom properties is not right - other DDCs reports a trigger by non-scalar properties in the `.userProperties` of an object, so for instance in the example `/Cube.userProperties.static_int` which is an ArrayProperty. this makes data unreadable or can crash some others DCCs ex : what maya can see ![image.png](https://archive.blender.org/developer/F10101478/image.png) - the userProperties can only be written on transform level, but the alembic standard is to do it on shape level. (don't look at maya for this, maya does it wrong too by default ) we should be able to choose if properties are at xform or shape level and default must be on shape normally **Exact steps for others to reproduce the error** add custom attributes on objects export alembic with custom attributes on inspect the alembic with abcls [custom-properties.blend](https://archive.blender.org/developer/F10099261/custom-properties.blend) [custom-properties.abc](https://archive.blender.org/developer/F10099242/custom-properties.abc)

william eguienta commented

2021-05-14 07:03:27 +02:00

Added subscriber: @kaiz3r

william eguienta changed title from ~~alembic attributes~~ to alembic attributes doesn't repect alembic standard

2021-05-14 07:04:24 +02:00

william eguienta changed title from ~~alembic attributes doesn't repect alembic standard~~ to alembic attributes doesn't respect alembic standard

2021-05-14 14:05:27 +02:00

Philipp Oeser commented

2021-05-14 17:00:30 +02:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2021-05-14 17:00:30 +02:00

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

Philipp Oeser commented

2021-05-14 17:00:30 +02:00

Seems alembic export supports Custom Properties on the Mesh datablock (shape level) as well?
#88275.abc

#88275.blend

Doesnt this work for you?

the userProperties can only be written on transform level, but the alembic standard is to do it on shape level.

You have the choice to put it on the object (transform level), the object data / Mesh (shape level) or both. Dont think we need a "standard" here if we can put it on both?

Seems alembic export supports Custom Properties on the `Mesh` datablock (shape level) as well? [#88275.abc](https://archive.blender.org/developer/F10102073/T88275.abc) [#88275.blend](https://archive.blender.org/developer/F10102074/T88275.blend) ![image.png](https://archive.blender.org/developer/F10102088/image.png) Doesnt this work for you? > the userProperties can only be written on transform level, but the alembic standard is to do it on shape level. You have the choice to put it on the object (transform level), the object data / Mesh (shape level) or both. Dont think we need a "standard" here if we can put it on both?

Philipp Oeser commented

2021-05-14 17:07:59 +02:00

If there is a standard for this, is this defined anywhere?

william eguienta commented

2021-05-14 17:44:19 +02:00

my mistake, it's the .arbGeomParam that needs to be on shape level...
thank you for the example files
I can confirm that, with your export too, the alembic can cause crash because of array being non scalar
is there a way to export as arbGeomParam in blender to compare it with maya ?
here is an abc from maya, that export by default attribute to arbGeomParam and that work in all our DCCs
custom-propertiesMAYA.abc

my mistake, it's the .arbGeomParam that needs to be on shape level... thank you for the example files I can confirm that, with your export too, the alembic can cause crash because of array being non scalar is there a way to export as arbGeomParam in blender to compare it with maya ? here is an abc from maya, that export by default attribute to arbGeomParam and that work in all our DCCs [custom-propertiesMAYA.abc](https://archive.blender.org/developer/F10102304/custom-propertiesMAYA.abc)

Philipp Oeser commented

2021-05-14 17:54:05 +02:00

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

Philipp Oeser commented

2021-05-21 11:10:28 +02:00

Sorry it took a bit to answer.

Trying to understand better:

the alembic can cause crash because of array being non scalar

Not sure why that is? Both your provided abc and the one I exported write scalars in to single-element arrays, found this comment:

   * Here Blender does the same as other software (Maya, Houdini), and writes
   * scalar properties as single-element arrays. */

So it seems to come down to .userProperties vs .arbGeomParams.
Or does this mean we are not allowed to write single-element arrays into .userProperties?

Found this other related comment:

  /* Return the Alembic schema's compound property, which will be used for writing custom
   * properties.
   *
   * This can return either abc_schema.getUserProperties() or abc_schema.getArbGeomParams(). The
   * former only holds values similar to Blender's custom properties, whereas the latter can also
   * specify that certain custom properties vary per mesh component (so per face, vertex, etc.). As
   * such, .userProperties is more suitable for custom properties. However, Maya, Houdini use
   * .arbGeomParams for custom data.

Having said that, what I find strange is that a CompoundProperty .arbGeomParams is always defined by blender, but then empty?

Do you have any reference or document where this standard is described?

Sorry it took a bit to answer. Trying to understand better: > the alembic can cause crash because of array being non scalar Not sure why that is? Both your provided abc and the one I exported write scalars in to single-element arrays, found this comment: ``` * Here Blender does the same as other software (Maya, Houdini), and writes * scalar properties as single-element arrays. */ ``` So it seems to come down to `.userProperties` vs `.arbGeomParams`. Or does this mean we are not allowed to write single-element arrays into `.userProperties`? Found this other related comment: ``` /* Return the Alembic schema's compound property, which will be used for writing custom * properties. * * This can return either abc_schema.getUserProperties() or abc_schema.getArbGeomParams(). The * former only holds values similar to Blender's custom properties, whereas the latter can also * specify that certain custom properties vary per mesh component (so per face, vertex, etc.). As * such, .userProperties is more suitable for custom properties. However, Maya, Houdini use * .arbGeomParams for custom data. ``` Having said that, what I find strange is that a `CompoundProperty` `.arbGeomParams` is always defined by blender, but then empty? Do you have any reference or document where this standard is described?

Philipp Oeser commented

2021-05-21 11:43:21 +02:00

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

Philipp Oeser commented

2021-05-21 11:43:21 +02:00

Here is an abc with Custom Properties written to arbGeomParams
T88275_arbGeomParams.abc

Does this also crash?

(this was done changing https://developer.blender.org/diffusion/B/browse/master/source/blender/io/alembic/exporter/abc_writer_abstract.h$113)
P2131: T88275_snippet



diff --git a/source/blender/io/alembic/exporter/abc_writer_abstract.h b/source/blender/io/alembic/exporter/abc_writer_abstract.h
index d3500394555..04b4f72990e 100644
--- a/source/blender/io/alembic/exporter/abc_writer_abstract.h
+++ b/source/blender/io/alembic/exporter/abc_writer_abstract.h
@@ -110,7 +110,7 @@ class ABCAbstractWriter : public AbstractHierarchyWriter {
   template<typename T>
   Alembic::Abc::OCompoundProperty abc_schema_prop_for_custom_props(T abc_schema)
   {
-    return abc_schema.getUserProperties();
+    return abc_schema.getArbGeomParams();
   }
 };

Having said that, what I find strange is that a CompoundProperty .arbGeomParams is always defined by blender, but then empty?

(this seems to be related to exporting UVs btw. not exporting UVs will also not define .arbGeomParams -- still find it strange...)

Here is an abc with Custom Properties written to `arbGeomParams` [T88275_arbGeomParams.abc](https://archive.blender.org/developer/F10133613/T88275_arbGeomParams.abc) Does this also crash? (this was done changing https://developer.blender.org/diffusion/B/browse/master/source/blender/io/alembic/exporter/abc_writer_abstract.h$113) [P2131: T88275_snippet](https://archive.blender.org/developer/P2131.txt) ``` diff --git a/source/blender/io/alembic/exporter/abc_writer_abstract.h b/source/blender/io/alembic/exporter/abc_writer_abstract.h index d3500394555..04b4f72990e 100644 --- a/source/blender/io/alembic/exporter/abc_writer_abstract.h +++ b/source/blender/io/alembic/exporter/abc_writer_abstract.h @@ -110,7 +110,7 @@ class ABCAbstractWriter : public AbstractHierarchyWriter { template<typename T> Alembic::Abc::OCompoundProperty abc_schema_prop_for_custom_props(T abc_schema) { - return abc_schema.getUserProperties(); + return abc_schema.getArbGeomParams(); } }; ``` > Having said that, what I find strange is that a CompoundProperty .arbGeomParams is always defined by blender, but then empty? (this seems to be related to exporting UVs btw. not exporting UVs will also not define .arbGeomParams -- still find it strange...)

Philipp Oeser commented

2021-06-04 13:24:39 +02:00

@kaiz3r : could you check the above please? (otherwise will be closed in a week)