Creating float64_t[2] attributes for alembic

[flowb]

Hi this is sort of a repost of this:

Adding uv data to alembic on export

Hi, I’ve been asked to build a script that replicates the behavior of this maya script: The goal is to add the root_uv data as a custom property to an alembic file so that it can be read by the UE Groom plugin. The maya script actually does a bunch of extra work that is probably unnecessary in Blender. The Maya script manually looks up the UV value based on the curve position and a nearby mesh. In blender, I’ve noticed, the strands already have a root_uv property that’s used by eevee, cycles…

I’m hoping the more nuanced subject-title might shake some replies loose.

Essentially I’m looking for information on how to create custom uv fields in alembic files. A colleague asked me to simplify a workflow they currently use for texturing hair exported from blender for use in UE’s groom system. Currently, they generate the hair, export it via alembic, then run a script on the alembic in Maya to add the property. The target is a classroom of students who are using blender.

Here’s what the result looks like from AbcEcho:

    CompoundProperty name=.arbGeomParams;schema=
      ArrayProperty name=groom_root_uv;interpretation=vector;datatype=float64_t[2];arraysize=10537;numsamps=1

that “float64_t[2];arraysize=10537;” bit looks like a 2 dimensional array structure.

As I mentioned in the other post, blender’s alembic documentation indicates that custom properties are currently added using the custom properties fields in the object properties, and that nested arrays are flattened into one dimensional arrays.

Does anyone have experience working with these types of structures in alembic, and might know how to go about working with them in blender?

Thank you