Is it possible to drive a channel primitive with CHOP, just like how we can control SOP parameters with CHOP? If so, how?

What's a channel primitive?
I'm afraid there is should be a screenshot to understand the question better

Ivan L
What's a channel primitive?
I'm afraid there is should be a screenshot to understand the question better

It's the thing you animate in Animate State, like tx, ty, tz. It's how SideFX's document call them:

https://www.sidefx.com/docs/houdini/character/kinefx/animatestate.html [www.sidefx.com]

Channel primitives are animation curves that are stored along with the geometry and are optimized for the animate state. When a control on a character is selected, channel primitives for that control are added to the channel list, and you can interact with them like regular channels.

In the older KineFX workflow, you animate Rig Pose's parameters. While it had some drawbacks, you can control them procedurally with CHOPs directly.

In APEX, you animate channel primitives (?), and I'm not sure how to do it procedurally. I guess the proper way is just extract them with APEX Extract Control, then do it in Rig Pose as before?

And even worse, Animation Layer is done with CHOPs too. So it means if you need layered animations, you have to extract both as KineFX animated skeleton, then mix them in a KineFX way... it also means the Animation Layer panel is useless for APEX animation now.

APEX based rigging and animation tools are in beta
So naturally there is a lot missing

- If you want to use CHOPs to modify or create channel prims it should be possible using VEX or Python, both can access chops and create/modify channel prims
Then just inject them back to the packed character before invoking

- CHOPs as well as CHOP animation layers have disadvantage of making the curves dense, which is often not what you want to happen when animating
So having CHOPs involved for that would be less than ideal and on top of that it would make an external dependency on CHOPs so the animation clips would no longer be self contained in the character

What will most likely need to happen is native support for animation layers using APEX based tools, since you want sparse layers to be evaluated during invoking rather than having to collapse them before

tamte
APEX based rigging and animation tools are in beta
So naturally there is a lot missing

More like in alpha (I've reported 15 APEX-related bugs. They're all actual bugs, not REFs or quality of life improvements.)

But thank you very much for the insight on CHOP's drawbacks.

- If you want to use CHOPs to modify or create channel prims it should be possible using VEX or Python, both can access chops and create/modify channel prims

Do you mean we can write python directly in APEX graph? Or you mean a Python SOP just before APEX invoke?

kodra
Do you mean we can write python directly in APEX graph? Or you mean a Python SOP just before APEX invoke?

In Python SOP or PrimWrangle if you want to modify them using VEX

Since you would be introducing external dependency in CHOP graph, you don't want that to happen during APEX evaluation as the chop graph may not even be available during the evaluation

Therefore if you sample CHOPs to create or modify channel prims its better to inject them back to the character as channel prims with already modified values

As long as you are in the same scene the chop link will still be live though so will be similar to motion FX even though not in the same APEX animate as the channels it's applied to

You can of course build APEX graph which will modify or create channel prims on the fly during the APEX evaluation, that'd be more like rebuilding chop operators, which for certain types of motion FX should be trivial