Houdini Transforming Alembic Instances Exporting to .ass

[Grezzybear]

Found an annoying problem recently in regards to rendering .ass files with instanced packed alembics. 

So the basic set up is packed alembic geometries being sent through a "Copy to Points" sop and are packed and instanced. These are then being manipulated a bit, and then being sent through an Arnold ROP to export a .ass file. These .ass files are then being sent to Maya to render and they have rendered great.
The issue I have discovered is after I pack and instance my packed alembics. I added a little processing to the "transform" prim intrinsic to give the instances a little rotation and scale the instance from 0 to 1. Rotating the instances through the "transform" prim intrinsic works great and renders fine. However, scaling the "transform" prim intrinsic matrix causes the render to send the instances to go all over the place randomly. The Houdini viewport shows the instances scaling correctly, but after exporting the .ass and rendering in Maya the instances go all over the place randomly. 

This is all I am doing to scale the instances. f@grow is just an animated attribute to drive the scaling of the instances.

matrix3 transform = primintrinsic(0,"transform",@primnum);

matrix3 scaleMatrix = ident();

scale(scaleMatrix,set(f@grow,f@grow,f@grow));

setprimintrinsic(0,"transform",@primnum,transform*scaleMatrix);

Does anyone have any experience with this? I cant upload a file just yet because its a work thing, but its possible I can recreate it. This is really driving me crazy so any suggestions would be great to just try something fresh!

Edited May 24, 2022 by Grezzybear
Added Transforming to title

[davpe]

hey, not sure about .ass format specifics, but for manipulating packed transforms i recommend this workflow:

https://vfxbrain.wordpress.com/2020/07/09/how-to-re-apply-packed-transform/

not sure thou if that will fix the .ass file. Haven't used arnold for years now.

cheers, D.