Hi Houdiniminded friends

Could you help me?
I have attached a hip file.

I would like to achieve the next effect. You are growing a selection over time (thus far working). When a selection reaches or extends to a primitive face this face starts to rotate from 0 to 180 degrees in one of its axes. However now when a face is selected it starts rotating not from 0-180 degree but according to its position in the animation in the primitive sop as a whole.

I do not know how to tell it to the primitive sop. Probably I have to write a custom VOP geometry node. or maybe there are expressions to achieve this effect.

Thank you in advance.

hi,
there are number of ways doing it depending on what you're trying to achieve.
I can't find out now the easiest solution but I'm sending you three other.

If you can define group membership procedurally this is fairly easy task, as you can base on it in transformation. Procedural membership is a primitive number for example.

When you'd like to use handmade grouping which vary during time like in your example, there is a another method. You can namely use partices as time counters in respect to how many frames elapsed after some primitive was added to your group. From that point it's easy to use this to lookup animation both procedural or key-framed.

See attached example.

One thing is terrible inelegant in it. The way I fuse unneeded particles. I just forgot how not to loop through geometry during every cook. One could use “Max particle” parameter in POPnet Tab but this doesn't give precise result.

Another method would be to use python script for storing history of group membership. This would be easy also but I intentionally didn't go this way as Houdini is meant to be code-less sulution . If you feel you need it though, just let me know.

hope this help,
cheers,
sy.

Thank you very much, I'm checking, I thought there is a simple solution.

Cool.

Well, perhaps the nicest thing in Houdini is that there is nothing like a one way to any direction. You can go wherever you want or where you fill comfortable. Note also that these are simple solution. “easy_procedural_way” consists with 3 nodes and 1 expression. Particles solution have3-4 nodes and 1 expression…

I've even tried yesterday scripting method. It's fairly easy also, it took less then 10 lines of python to store group membership history. Not very procedural though as it uses hardcoded cache which probably would make trouble in bigger scenes. but it's fast also


CHOPS are the way to go but I'm not very familiar with this beat ops:


cheers,
sy.

Meantime a friend has done the task with chops, he used a different approach, probably he is willing to share, but I have to ask for it. However your solution seems good too.

Do you know some good tutorials which could help me to dig into expressions, scripting, VOP SOP creation, CHOPs in houdini, besides th online help in Houdini?

Thanx. Best regards.

he he

In the meantime as a personal penance I did it with CHOPS also - I look on chops always on the last place which is a really bad habit

This is the most elegant and fastest solution for sure.

Let's compare them!

cheers,
sy

I'm waiting for his approval.

regget
Do you know some good tutorials which could help me to dig into expressions, scripting, VOP SOP creation, CHOPs in houdini, besides th online help in Houdini?

This is issue like a Pacific Ocean!

As to CHOPS:
Docs + OldSchool blog with a number of QT about chop usage.

As to Expression:
the only way to learn them except cookbook in help is to skim through them from time to time in text port:

-> exhelp -k chop

will give you all chop related expressions


Every context and entity in Houdini have in assistance number of expressions. So it's not so easy to just learn it. But there is nothing to learn actually as everything you need to know is an expression name which can be easily found with exhelp if you know what you're trying to do.

So the hardest part of expressionism is a conceptualization not expression usage. If you can NAME your problem you're almost solving it.


As to VOP SOPs:
The best tutorials I know on that are old 3dbuzz videos about water ripples displacement + FrenchOP old tutorials on dividing geometry with some noise function in VOPS. Both of them are really great!

As to Scripting:
Just learn python since it really rocks and will replace hscript piece by piece.
There are currently no sources about specifically python in Houdini except nice chapter in docs.

Please note also that there are some new stuff in horizon like a new VTMs from 3dbuzz and new cmivfx DVD about VEX!

hope this help,
sy.

Thank you for the helpful tips and infos.

I've checked python.org, and I think I'm gonna start learning it. My father is a programmer, so I'm trying to find some time to discuss things with him.

Here is the chop version of the effect by the courtesy of a friend.

Thanx goes to him too, and to SYmek by my part.

hi!
Is there a node based distance calculation?
I mean this is very simple too, using the distance expression, just want to find various ways doing this in H.

Try measure sop, or the one, a turbo version of this found in Houdini exchange.

thanks! koszi!