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Hair curves exported to alembic cannot be used as ue4.26 groom hair
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Description

System Information
Operating system:Windows 10(1909)
Graphics card:AMD R54600U

Blender Version
Broken: 2.91.0,2.90.x,2.8x.x

Short description of error
Hair curves exported to alembic cannot be used as ue4.26 groom hair [so simulation would take place in UE]
When simulation is turned on, the hair is in a mess and appears to have lost weight.Is possible to converted directly from particle Hair to Hair curves?

Seems like UE requires special properties to be defined and written in the alembic file for this to work properly, see https://docs.unrealengine.com/en-US/WorkingWithContent/Hair/AlembicForGrooms/index.html

Exact steps for others to reproduce the error
1,Create particle Hair
2,Convert particle Hair to Mesh
3,Convert Mesh to Curve
4,Select curve and export to alembic(100 scale and only frame 1,only selected)

Event Timeline

Philipp Oeser (lichtwerk) changed the task status from Needs Triage to Needs Information from User.Dec 16 2020, 12:28 PM

Not quite sure I understand correctly:

Is possible to converted directly from particle Hair to Hair curves?

https://docs.blender.org/manual/en/dev/files/import_export/alembic.html#particle-systems

if you take this file with dynamic hair:

you'll end up with said animated curves in alembic (by just exporting to alembic with default settings):

What exactly is not working for you?

Ag2S (Ag2S) added a comment.EditedDec 16 2020, 1:08 PM



The above is the curves hair abc file exported by blender, and the following is the curves hair abc file exported by Maya xgen. The abc file exported by blender cannot be correctly simulated in UE4.
https://docs.unrealengine.com/en-US/WorkingWithContent/Hair/AlembicForGrooms/index.html
https://docs.unrealengine.com/en-US/WorkingWithContent/Hair/XgenGuidelines/index.html
https://github.com/EpicGames/BlenderTools/issues/136

Videos seem to be recognized as Audio?

Link to the issue on the UE tracker seems dead for me...

Videos seem to be recognized as Audio?

Link to the issue on the UE tracker seems dead for me...

its hevc format

its hevc format

OK, plays locally here, at least my firefox doesnt like it though...

Link to UE issue tracker would still help

Philipp Oeser (lichtwerk) changed the task status from Needs Information from User to Needs Information from Developers.Dec 16 2020, 1:41 PM

Oh, afaics, the simulation takes place in UE [makes sense] and it needs special properties written to the alembic.

That might get classified as feature request or TODO, depends on @Sybren A. Stüvel (sybren).

Philipp Oeser (lichtwerk) changed the task status from Needs Information from Developers to Needs Information from User.Dec 16 2020, 1:41 PM
This comment was removed by Sybren A. Stüvel (sybren).
This comment was removed by 888 (wiwa).
This comment was removed by 888 (wiwa).
This comment was removed by Sybren A. Stüvel (sybren).

its hevc format

Please stick to formats/codecs that are widely supported in webbrowsers. WebM/VC9 and MP4/h.264 are the safe choices.

This is a feature request, and not a bug report, though. It is notoriously difficult to get curves in Alembic to work cross-DCC, as curve parameters are highly under-documented in Alembic.
As for the custom properties that need to be defined, it might be possible to write those by actually setting them as custom properties in Blender. These are exported to Alembic since Blender 2.91.

Is there a way to convert this to a feature request?
Someone was looking for a workaround here, as well as I.
https://devtalk.blender.org/t/creating-float64-t-2-attributes-for-alembic/24498