Heya,

We're currently trying to export Pref from Maya to use in Arnold in Houdini. We are writing this as a vector in to our alembic at export stage using an in house plugin. Houdini reads this as a “color”(Col) attribute. However Arnold doesn't seem to want to recognize this as Pref at render time. If I remake the attribute and Houdini recognizes it as 3flt(Pos) or 3flt then it works.

Question is..

How does Houdini determine whether an existing vector attribute is a Color(Clr) or Position? They seem identical to us when written.

Any help much appreciated…

it just depends on how you write them to .abc as if you look how they are stored there you will see the difference in interpretation

as a color:
ArrayProperty name=Pref;interpretation=rgb;datatype=float32_t;arraysize=100;numsamps=1

as a point:
ArrayProperty name=Pref;interpretation=point;datatype=float32_t;arraysize=100;numsamps=1

as normal:
ArrayProperty name=Pref;interpretation=normal;datatype=float32_t;arraysize=100;numsamps=1

so just make sure your inhouse plugin writes them correctly

EDIT: as a side note you may not want Pref to have any interpretation and keep it as generic float array
since if it is point(Pos) it will get transformed by nodes that transform attributes which may not be desired if it represents rest position

EDIT2: also can't imagine arnold not recognizing (Col) attributes as that's the most common for vertex color properties

Thanks very much Tomas you have answered both my obscure technical questions in the last 10 years

I'm not sure how the plugin is working and how it's writing attributes it's an external tool we created in C++ years ago so will look in to that with the team.

Yes I don't understand why it doesn't recognize it as a col attribute in this specific scenario.