Hi,

Just noticed something strange.
To get a nice particles trail from an object, I use impulse activation with the right number, accurate birth and increase oversampling on the popnet until there are no gaps in the trail.

However i just noticed that this didn't work when the object's movement came from an expression in a transform node, for example sin($F)*5 in Y.
(the network is a polygon circle piped into a transform piped into a popnet)
In this case, I still have gaps between the particles, but several particles stuck on top of others (as many as the oversampling, which seems logical).

If the movement is keyframed or comes from chops, it works as expected.

I guess it's to be expected and it's because the transform node is cooked only on each frame, because the oversampling doesn't apply to it.
So, is there a way to force a node to cook between frames ?

I can work around this going to chops, but just being curious!
Thanks!

Try using sin($FF)*5. The $FF makes sure that Houdini will take into account the sub frame cooking caused by the over sampling.

A default oversampling of 1 will cook the popnet once per frame. While 10 for example is 10 times per frame. However, $F will be evaluated as the same for each of the 10 cooks that occurs in the given frame time because it evaluates as an integer. $FF will cause the frame number evaluation to be a float value, giving you in betweens.

An example of this is to disable Integer Frame values in the animation options on the playbar. Then scrubbing to say something like 20.478. Now put $F in a parm field and it will show 20. Put $FF in and it should show 20.478.

Hope that helps,

Thanks a lot, works fine now, completely forgot about the $FF variable ops: