Solver sop seems like a handy node if I just just figure out how to incorporate it properly. Here's my scenario:

I've a a long strip of points travelling along in X (like rocks on a conveyor) and each rock has a float attribute that's a random value between 0 and 1. When each point hits a certain position in X the random value gets added to every frame which is where I though the solver sop would come in. Then at a further position in X the counting stops, and a delete node gets rid of all the points who's random value is above a threshold.

I was using a group by bounding volume to determine where the counting should occur but I can't combine the counting bit inside the solver sop with the grouping bit that comes before.

How do I get the adding wrangle in the solver sop to use the group that's changing frame to frame.

Alternatively what other techniques would people use to achieve the same result?

cheers,

A>

This seems to work. I added an attribute called trigger to the points in the triggerGroup, then use this to modulate the random_0_1 attribute in the solver.

Thanks mrCatfish,

that works perfectly, vops rather than vex and wrangles is much more familiar given my softimage history but somethings tells me i'll need to grasp vex properly at some point as i've zero coding experience whatsoever. Am I right in thinking that groups are actually just attributes under the hood?

Yeah, some things are definitely easier to do in VOPs, and some in VEX.

Internally, yes, it seems Houdini groups are attributes, and you can even see group membership in the geo spreadsheet.