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Alembic - Aplly scale doesn't work with the Mesh Sequence and hair
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System Information
Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce RTX 2070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 418.96

Blender Version
Broken: version: 2.80 (sub 57), branch: master, commit date: 2019-04-14 19:18, hash: rB860a9f979d60
Worked: (optional)

Short description of error
I have lots of brushed hair on a character. Scaling is crucial to hair systems, and when I import an Alembic without animation, All I have to do is to scale the alembic to the size of my character, apply scale and copy all the hairs systems - works like magic.
The problem begins when I import an animated alembic, no matter what I do the hair goes craze and when I apply the scale it jumps back to its original size and messes the hair again.

Exact steps for others to reproduce the error
All I need to do is to import the alembic' copy weight paints, copy all the particles systems, scale the Alembic to the right size, apply scale - and it jumps back.
tried to import an Alembic with smaller scaler beforehand but didn't work either

RAR file with Blend and Alembic



Event Timeline

Serj Maiorov (printerkiller) renamed this task from Alembic - Aplly scale doesn't work with the Mesh Sequence to Alembic - Aplly scale doesn't work with the Mesh Sequence and hair.
Sebastian Parborg (zeddb) triaged this task as Confirmed, Medium priority.

Unsure if applying scale is supported for sequence caches. @Sybren A. Stüvel (sybren) any input on this?

Applying scale is not supported. This changes the mesh data, which is replaced with the data from Alembic. Try creating an Empty, set it as the parent of the imported Alembic object, and scale the Empty.

Tried to do that but it still breaks the hair

Is there an alternative to that workflow? Because we use real world scales to be consistent with lighting and materials over live footages. How can we interchange hair between Alembics and still maintain real scales?

Sybren A. Stüvel (sybren) lowered the priority of this task from Confirmed, Medium to Needs Information from User.Aug 1 2019, 4:42 PM

Blender's hair system is very picky when it comes to the mesh it's attached to. Especially when grooming, it is vital that the face & vertex indices remain the same. Are you sure that the mesh in Alembic didn't change between grooming the hair in Blender and getting these errors?

Please provide us with an as-simple-as-possible test file. This file has various hidden (and thus probably irrelevant) objects, three different hair systems, and a subdivision modifier that may or may not influence the result.

As an alternative workflow, what is stopping you from exporting to Alembic in the correct scale, so that later stages in the pipeline can just use the file as-is?

This is probably the same issue as T63534.

Since last asking for information it has been 7 or more days, due to the policy of our bug tracker we will have to archive the report until the requested information is given.

This issue is probably solved in ee8aad79c159. If not, please provide the requested information.