I was randomly trying to generate more test data and stumbled onto one possible issue.

In Houdini I created a mesh with 4 triangles and a Cd attribute per triangle:

• Triangle 0, Cd value = [1, 0, 0, 0]
• Triangle 1, Cd value = [0, 1, 0, 0]
• Triangle 2, Cd value = [0, 0, 1, 0]
• Triangle 3, Cd value = [0, 0, 0, 1]

This is what it looks like in Houdini:

If Import the alembic in Unity and apply the Alembic/Overlay material this is what I see:

To be completely honest, I don't really know what I'm doing 😅, but I feel like the colors shouldn't appear to blend like this. I would assume to the same thing as in Houdini

I've attached the alembic file and the Houdini scene used to generate it in case it's useful (it's a .zip because Git doesn't want .hip/.abc files...)

plane_4tris_facecolor.zip

Found one more problematic case 🙈. The facecolor appears incorrectly "blended" if a mesh contains polygons with varying numbers of sides (ex: if a mesh contains a three-sided polygon and a four-sided polygon).

The first polygon appears correct and the others are "blended":

Houdini	Unity

I've attached four files that can be used for testing facecolor_samples.zip :

• plane_triQuad_facecolor_1_24fps.abc = 1 three-sided polygon, 1 four-sided polygon
• plane_triNgon_facecolor_1_24fps.abc = 1 three-sided polygon, 1 five-sided polygon
• plane_quadNgon_facecolor_1_24fps.abc = 1 four-sided polygon, 1 five-sided polygon
• plane_ngonTriQuad_facecolor_1_24fps.abc = 1 three-sided polygon, 1 four-sided polygon, 1 five-sided polygon

I believe that we/Unity create a sub-mesh for every type of polygons. For example: if an alembic mesh contains both triangles and quads, all triangles will be grouped in a submesh and all quads will be grouped in another sub-mesh.

I'm not sure what the behavior is for polygons with more than 4 sides (ie: are they grouped by polydon-side-count or all together in a single sub-mesh)

I'm really not confident about the quality of this information though. I feel like someone reliable said this to me but it's in a very dusty corner of my memory, haha. I'm including it just in case helps for debugging

QA approved 👍!

I'm a bit limited in testing and knowledge around this area but every case I could think of seems to work now using the Color/Cd attribute + Alembic/Overlay material 🎉

Tested on:

• 2023.2.0b15 (Windows only)

LGTM!

I ran it and it seems to work. The code logic follows from what I can tell. Just some wording stuff.