[Sidefx-houdini-list] Hi

Alex Czetwertynski disciple1 at gmail.com
Mon Feb 8 22:17:41 EST 2016


You should really look up Unix file navigation, as without an understanding
of that, all of these expressions will be hard to understand, and mostly
you won't be able to re-create them.  All pre-GUI stuff, but still
extremely important and useful.

Let's say it this way.

Opinputpath only works in relation to nodes that are plugged into another
node.  They specifically refer to a node that has a direct connection, a
line, going from one node to another.  Without this connection, Opinputpath
is useless.

Now imagine you have two nodes, side by side.  They are not connected.  One
is a box, the other a sphere.
Now say you want to grab a parameter from the sphere and apply it to the
box.  For example scale.
So you would go into the scale parameters of your box and type something
like ch("../sphere1/size...")

You can do this because what you are telling Houdini is "Go from me to this
other node (../) called sphere 1 and grab this parameter (scalex or y or z
or radius or whatever).

You don't have to memorize this stuff, just copy a parameter you are
interested in and do a "paste relaitve references" to see how it is
written.  Once you see that a few times you will remember the syntax.




On Mon, Feb 8, 2016 at 10:04 PM, Crest Christopher <
crestchristopher at gmail.com> wrote:

> The "." & ".." always mean the node above, not the hierarchy; if so, that
> is one thing I was getting hung up on.
>
> You mentioned that the expression needs the name of the node that has the
> incoming connection into it; but you didn't apply the expression yet ? ;-)
>
> If you applied the expression centroid, "." is the current node if there
> was another node I assume that would be ".." ! ;-)
>
> When you say plug; you mean the first node in the hierarchy, which you
> skip the torus and go straight to the transform node ? If you had another
> transform node that would be
> centroid(opinputpath(".",1),D_X) ?
>
> And so D_X stands for... ?
>
> François Duchesneau wrote:
>
>> opinputpath returns the path of a node. Let's say we have a torus at
>> /obj/geo1/torus1. This torus is plugged into Transform Sop. You want to
>> have the pivot of the transform to be the center of the torus. The
>> expression "centroid" can you give that.
>>
>> Now the centroid expression requires the path to a node. To get the path
>> of torus1 node procedurally you use the expression "opinputpath". This
>> expression needs the name of the node that has the incoming connection into
>> it. In this case the node is the one that has the expression written to it.
>> The special "." means this node. ".." means the node above. Don't think the
>> node above means the torus, we're talking about the hierarchy here, above
>> is the parent /obj/geo1.
>>
>> So in the Pivot X channel you would write the following:
>> centroid(opinputpath(".", 0), D_X)
>>
>> The first parameter of centroid is the current node. Then 0 is to tell
>> we're querying the first plug. The second plug would be 1 and so on but you
>> don't have two plugs on a Transform Sop anyway.
>>
>
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