Consider the following hierarchy:


In my particular case, if I use a TimeShift node to 'framehold' child3 specifically (cook and eval at a single frame), it also frameholds child 2. But not child 1. No instances in play. Child 2, the one being affected incorrectly by the TimeShift, is being created by a SOP Import, whereas the others are alternately loading static geo or simple animation.

What might cause the timeshift node to affect other prims (but not all) which are not specified in its prim pattern?

Hey Tim!

I appreciate the confusion here. The TimeShift node can do a combination of things:

1 - It can force the input node to be cooked at a certain time (cookinputattime toggle). This means that any Houdini-based animation will be frozen at the specified cook frame. This affects *everything* in the incoming stage.

2 - It can replace USD time samples with the value from a certain time (evalattribsattime toggle). This can be done selectively on a prim-by-prim basis, and *this* is where the primpattern parameter comes into play.

So, back to your example, cookinputattime is on by default, and *that* is why /child2 is frozen. /child1 is not frozen because it (very likely) has USD time samples, and is not in the primpattern (where you're specifying /child3).

Does that make sense?

I'll see if we can at least make the UI a bit more obvious.

I'd have to dig and ask around to understand how practical it would be to have the primpattern be taken into account for the Houdini animation. At a minimum we'd need to cook the input stage twice, but it may have a whole world of complexity beyond this that I'm unaware of.

- Rob

Thanks for explaining this, Rob. This makes perfect sense actually. I think my expectation was exactly what you describe at the end there. In some situations the load method (SOP vs USD) may be hidden from the end user, so all they have to work with may be the scenegraph itself. It sounds tricky to solve, but if the primpattern could be taken into account for the Houdini anim, that would be considerably more intuitive and maneuverable.