https://www.youtube.com/watch?v=QQ9HogEWcT0 [youtube.com]
0:07 - 0:15 second

So I'm curious as of how they created this effect and wish to replicate it in Houdini, but I'm still a novice in Houdini.

I was thinking something along the line example:
1. Create a test geometry PigHead
2. & to create irregular point within the Pighead.

3. Force all the points position to shift to a single point position? example Point 001
4. Then add in velocity to move them around or back to their original position?

So how do I achieve step 3-4 in this case?

Any help would be appreciated!

I've done this with particles.

- Make particles flow through the surface ( double cross product technique )
- Make each particle leave a trail
- With add sop connect this trails based on some custom attribute
- Apply poly wire sop

How do you do the “- Make particles flow through the surface ( double cross product technique )”?
Any possible example or hip file to look at?

- Shoot your particles toward the surface
- Take the particle's velocity, cross it with the surface normal, cross the result with the normal again, call this resulting vector “flow”, all this normalized.
- Call the ( closest pos on the surface ) minus ( the particle's position ) “tow”
- Make your force ( flow+tow ) * someMultiplier
- Make the particle lose velocity, something like this v@v *= 0.8;

I'll find some time tomorrow to make a hip file if you have trouble.

Having trouble understanding this part
“- Take the particle's velocity, cross it with the surface normal, cross the result with the normal again, call this resulting vector “flow”, all this normalized.
- Call the ( closest pos on the surface ) minus ( the particle's position ) “tow”
- Make your force ( flow+tow ) * someMultiplier”

Would be great if you can spare some time to make the hip file tomorrow.

Here you go.

I'll have to find some time tonight or tomorrow to comment it with stickies if you're having trouble making sense out of it.

Thanks for the hip file. Currently, I'm only having trouble understanding the part of the “POPVOP”. But overall it's what I'm looking for. Thanks a lot.

This thread was interesting so I've been following it.

Looked at the hip file and see the first instance that the attributes flow and tow show up is in the popnet node.

Dived into that and they are there in both the popobject and popsource nodes.

I thought you may have generated those attributes but it seems after looking through the parameters of these nodes that the popnet automatically creates these attributes?

I tried looking in the docs ( and perhaps I'm not looking in the right place ) as I was curious to know how these attributes are created, how they are derived, what they represent data wise.

Can't seem to find that info.

But thanks for posting the hip file…nifty trick. It's appreciated.

No, no. I created them in the popvop with bind exports.

I called it flow to represent that it's a vector that kind of flows through the surface. And tow as in towards the surface.

Ah..ok..I see…that reminds me about something I heard in the last while from a tut video.

It was saying that inside things like popnets the data doesn't always “flow” in a linear manner like what one would assume in an another network, say a circle followed by a transform node.

When I looked in the network I only middlemoused on the two nodes at the start of ‘chain’ of connections, so I missed looking at that popvop node; Which shows your set up when you dive into that node.

Thanks for pointing me in the right direction.

Is any possibility for an update on the hip file with some sticky notes explaining the workflow inside the POPVOP net?

Thanks a lot.

Hello guys, enjoy the file, and don't drink and drive.

Thanks for this A-OC.

I'm still somewhat new at VOPs which is funny because I've written alot of my own vex functions, but VOP nodes and connecting them together is still a bit ‘odd’ for lack of a better word, to me.

I know you can click on the nodes to see the VEX used for them, but your stickies are very usefull in helping me understand what is going on. Thanks again.

Thanks a lot for the hip file, A-OC.

You're welcome. Glad you liked it

As for vops oddness, I don't think it's any different than sops. They take inputs, do some magic, and produce outputs, but they work with numbers rather than geometry.

The difference I was speaking of is that in your example, you ‘create’ the binding within the popvop ( ‘tow’ and ‘flow). But the popvop is preceded by the popsource node and if you middlemouse the popsource node you can see what you created in the following node. Like it got ’fed back' to the previous node.

Usually us ‘newbies’ do things in Houdini like put down a sphere node followed by a transform and so on, so we start to see things in a linear way as far as connecting nodes together.( An assumption that ‘data’ is always flowing linearly through the connections in a top down manner ).

…put down a delete node ( for a certain number of points ) following a poly…middle mouse the poly will show a different number of points in the poly node vs. middlemousing on the delete node.

…the only other exception I know ( and there must be others ) is copystamping; As it gives the appearance of the expression reaching back ‘up’ into the network to make changes…

Ah ok, but then you mean wiring nodes in DOPs. Then yes, it uses a different paradigm than SOPs and VOPs. I agree it's harder to get one's head around it.

I remember reading a couple of pages of the book The Magic of Houdini. It's the only place I've seen DOPs well explained. Far better than Houdini's docs, which I think need major attention.

The book is pretty old, around 2008 I think, but it's definitely worth reading the dynamics section at least.

It just occurred to me, maybe you're not aware that a POPNET is actually a DOPNET ???

“…POPNET is actually a DOPNET ???”

No I'm not lol.

Thanks for the “The Magic of Houdini” reference…seems like that book is out of print ( being about 10 years old now ).

It's going for $119 on Amozon used, over $300 + new.

Managed to find an excerpt from it ( old news link from sidefx ).

Looks like good content.