Hair curves exported to alembic cannot be used as ue4.26 groom hair #83838

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opened 2020-12-16 12:18:43 +01:00 by Ag2S · 21 comments

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)

**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)
Author

Added subscriber: @Ag2S

Added subscriber: @Ag2S
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Added subscriber: @lichtwerk

Added subscriber: @lichtwerk
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Changed status from 'Needs Triage' to: 'Needs User Info'

Changed status from 'Needs Triage' to: 'Needs User Info'
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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:
#83838.blend

you'll end up with said animated curves in alembic (by just exporting to alembic with default settings):
#83838.abc

What exactly is not working for you?

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: [#83838.blend](https://archive.blender.org/developer/F9512849/T83838.blend) you'll end up with said animated curves in alembic (by just exporting to alembic with default settings): [#83838.abc](https://archive.blender.org/developer/F9512851/T83838.abc) What exactly is not working for you?
Author

blender.mp4
maya-xgen.mp4
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

[blender.mp4](https://archive.blender.org/developer/F9512962/blender.mp4) [maya-xgen.mp4](https://archive.blender.org/developer/F9512963/maya-xgen.mp4) 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
Member

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...
Author

In #83838#1076373, @lichtwerk wrote:
Videos seem to be recognized as Audio?

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

its hevc format

> In #83838#1076373, @lichtwerk wrote: > Videos seem to be recognized as Audio? > > Link to the issue on the UE tracker seems dead for me... its hevc format
Member

its hevc format

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

Link to UE issue tracker would still help

> its hevc format OK, plays locally here, at least my firefox doesnt like it though... Link to UE issue tracker would still help
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Changed status from 'Needs User Info' to: 'Needs Developer To Reproduce'

Changed status from 'Needs User Info' to: 'Needs Developer To Reproduce'
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Added subscriber: @dr.sybren

Added subscriber: @dr.sybren
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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.

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.
Member

Changed status from 'Needs Developer To Reproduce' to: 'Needs User Info'

Changed status from 'Needs Developer To Reproduce' to: 'Needs User Info'

Added subscriber: @wiwa

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

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

In #83838#1076391, @Ag2S wrote:
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.

> In #83838#1076391, @Ag2S wrote: > 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](https://wiki.blender.org/wiki/Reference/Release_Notes/2.91/IO#Alembic_.26_USD).

Added subscriber: @khyota

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Reference: blender/blender#83838
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