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Variance, Conditions, and Velocities

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Like many, I'm new to Houdini. I am using a single file to try to make some practical use of the application while I try new techniques.


I've attached my file. Here is are the things I can't seem to figure out in general, in order of difficulties.


  1. Passing velocities to DOPS from SOPS? - I'm trying to fracture geometry which i can do, but I want to only allow the Voronoi node to turn on when a velocity is at a certain threshold. In my Geometry Spreadsheet it is showing velocity of 0. I've tried many things and can't seem to give it velocity.
  2. Variance - I'm trying to give the gravity node (or any node) a variance of force. Gravity is ~ -9.8, but I want to do something like maybe "between -9.8 and -15." I've also tried things such as "fit" or "rand" but it didn't seem to work.
  3. Lastly, this isn't so much conditions in general that I'm confused about. But one thing I like to do is kill particles in other applications when they are out of view of the camera. So in my file, I'm trying to kill the DOPS fractures and soon to be POPS when they go below "number" in the Y axis. I added a delete node and tried "if(@P.y< -1, 1, 0)" in the DOP network, but I don't think I'm using it the way I should...Just to tag along onto this one too, since POPS and DOPS are now unified, how would I go about applying the same kill/death technique to POPS too?

I appreciate the help as I'm still learning. I attached my file to tear part if needed. Thanks :D!






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1. fracturing is using primitive group called ineligible to ignore objects during fracturing

to make pices ineligible for fracturing based on velocity you can use Geometry Wrangle (on Points):

setprimgroup(0, "ineligible", @primnum, length(@v) < 7 );

Purple Node in example file


2. POP Force with force as 0,-1,0 and VEXpression:

force *= fit01(random(@id), 9.8,15);

Green Node in example file


3. you can use POP Kill, but that will be deleted on next frame, so Maybe better is Geometry Wrangle (on Points):

if (@P.y<-1) removepoint(0,@ptnum);

Blue Node in example file


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Thanks Tomas! I'll dissect this ASAP. I'm coming from Max, so I'm so used to Thinking Particles and visually connecting data. 


I notice you're in New York at Method. A few years ago when I was at Pixomondo, we had a Tornado shot that you guys took over(Or whoever was there at the time). We were like "Noooooo, those buttheads  :P !"


But thank you again for replying so quick. I spent the entire day while simming on my laptop just trying to kill these particles.




Michael :D 

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