HI, this is just for fun, i'm not doing anything. So I tried to use an expression to drive the checkbox. For example i created a tube in sop level, go to detail tab, there's checkbox which control ‘End caps’, then i simply put expr : $F<30In the parameter window, i can see it drives the checkbox on and off as i wish , but in viewer there's no change. i'm just confused , as comparison i mainly use Nuke (foundry) where i can use python script to control almost anything. Anyone have any logical explanation for this? Again i'm just playing with scripting… just curious.

Thanx.

The node may not consider the toggle to be something that changes over time, and always evaluate it at t=0. What node and toggle parameter are you working with?

twod is probably right
End Caps Parameter of Tube SOP is not intended to be animated and is not evaluated over time
try to animate it by keyframes, no luck either

I must say I'm seeing this behavior for the first time, there is not much parameters in Houdini that cannot be animated
You have just picked the wrong node to try your expression on

Thanx, that make sense for the Tube/cap. What i'm really trying to do is i'm working on DOP. I want to play with active/deactivate the simulation to combine simulation with manual keyframe. Ussually there's couple ways to achieve the goal in Houdini. So the first method is using RBD keyframe active to control it , this way is working fine. Then i'm just trying to find an alternative way, i was thinking i can simply keyframe the ‘create active object’ parameter in the RBD object node. But in fact it was calculated at t=1 or at initial state. so i can't force it to recalculate it overtime.

thanx