Hi, sorry if this is obvious stuff (and it probably is). I've been experimenting with Houdini for a while now and I'm loving it so far, but this stuff is holding me back, so I decided to ask for some guidance.

I guess the main problem is i don't know how to correctly address and drive SOP-level Attributes (in VOPs and SOPs) for individual components in general.

For instance, I'm trying to make basic bendy limbs and i want to drive an individual Line points with SOP-level Nulls.

So Null1 drives point 0, Null2 drives point1 etc.

On one hand, in VOP SOP, I Import-Attribute a Null's position P(4f) value and i try to plug it into a Set Attribute node P(4f), but no matter how i set it up I can't get it to work.

On the other hand, forgetting VOP SOP for a while, I would like to drive a Transform Position value with a SOP-level Control's (or Null's) P(4f). How would i reference the P(4f) by expression?

If any of you could point me in the right direction I'd appreciate it.

I think we have couple ways , for example you can driving your points from nulls with Point SOP.

in the Attached project I used python for taking position of each null and use this position for position of specify point on the line. 8)

NOTE on't forget that number of nulls should be same with number of points !

Thanks Joker386.

It works great and does solve my problem at hand, however it doesn't really answer my general question. There are two reasons:

First of all, you're taking nulls from the scene level, which i would like to avoid sometimes, so I still don't know how to address the unexposed P(4f) parameter of a SOP-level Null / Control.

Second, I would like to know how to properly get and set this data in a VOP SOP (with a SOP-level Null), since I can't see myself doing python expressions in a day to day workflow just yet (no Python knowledge or good memory for syntax and I'd prefer VOPs anyways.;-))

Thank you very much though, you got me interested in going the Python route for expressions.

If you were willing to take a peek at my scene, it's attached below.

Filip Tarczewski
Second, I would like to know how to properly get and set this data in a VOP SOP (with a SOP-level Null)

I don't understand the question. In your file, vopsop2 seems to do exactly what you're asking already.

There must be something missing then, because moving the nulls doesn't make any change to the line points' position.

Which “nulls” are you referring to?

Sorry, I mean the nodes plugged into the vopsop2 1,2,3 inputs. I tried with nulls and controls. The point is i can't get either to drive the points of the line. As it is, the vopsop2 doesn't seem to be doing anything to it.

Hi, Filip,

not an expert, but i think you're doing it wrong, “nulls” at the sop level are empty nodes, “control” node is a bunch of shape presets, but any animation, if possible, should be done at object level. You should probably at least import (object merge) nulls from object level as it will be easier to animate.

set attribute node doesn't work in “vop sop” it works in “attribute vop sop” as it is a cvex function(don't know why it is accessible in vop sop).

is this what you were trying to do?

Thanks owlYzarc, that's exactly what i wanted to do in this case. I knew i was doing something wrong. I'll have to look into AttribVOP, I didn't even know of its existence.

What is the difference between VOP SOP and Attrib SOP exactly though? Help descriptions don't help much:

Attrib VOP
Runs a VOP network to modify geometry attributes.

VOP SOP
Contains a VOP network that can manipulate point attributes.

Sounds to me like both should be able to move points (isn't point position a point attribute, and point a piece of geometry?). Is it that VOP SOP can't address individual components, but rather loops through all of them?

well, as far as i know:

VOP SOP - is visual representation of VEX
goes through all the points simultaneously
has import attribute vop
has add attribute vop
can't create (add vertex/prim/point) or delete geometry

ATTRIB VOP (sop) - visual representation of CVEX
CVEX is newer and (I suppose) faster, but there are some differences.
goes through all the points/verts/prims/objects(detail) simultaneously
has get/set attribute
can create or delete geometry

so i guess help sort of states it with “points” vs “geometry”

So basically I can think of Attrib VOP as a newer version VOP SOP, Attrib VOP being the more flexible and powerful one?

Is there a help page or a chart explaining the differences between the two in depth one could use as a guide to choose the right tool for the job?

Probably yes.

anim
in general, VEX/VOP nodes based on CVEX are more generic and the trend seems to be steering away from sop/pop specific nodes like Point Wrangle/Vop Sop in favor of Attrib Wrangle/VOP, so while there are still some functions that are unique to Point Wrangle, in the future this gap should be closed and you should have all this power and much more in Attrib Wrangle (and other CVEX nodes like Geometry Wrangle DOP, POP Wrangle DOP, Volume Wrangle…) and their VOP equivalents

http://forums.odforce.net/topic/20891-attribwrangle-vs-pointwrangle/#entry124901 [forums.odforce.net]

attrib vop should have (almost) everything vop sop has + more, haven't seen any chart or help page about it.

Thank you for the clarification owlYzarc, and thank all of you guys for helping me out and sharing your knowledge. I have a long way to go, but at least now i know where to look and poke around. Kudos to you!