I've been trying to do some String Art [en.wikipedia.org] in Houdini.

The patterns are fairly easy to achieve with disjointed segments that can then be fused into a single guideline for further operations, i.e. to make it a thread with some thickness. However, some parameters value create one or more overlapping pattern - see attached scene that has many pentagons on top of one another.

A human would avoid that easily, i.e. skipping to the next nail that hasn't received a thread or skipping to a nail that is connected by fewer threads than the previous nails.

In a detail wrangle I tried to write an attribute to each point the thread was visiting, so that eventually I could skip points that had been visited already. This doesn't seem to be possible as the attribute written within the wrangle on a point doesn't seem to become immediately available, instead, only the next node sees it. It appears the wrangle makes a read-only copy of the input geometry and the attributes are written on the write-only output geometry.

Can somebody confirm my understanding and suggest a solution?

If you want to do this in a detail wrangle, you have to create an array and store the visited states there so you can read and write to them in the same code.

Thank you animatrix, I was thinking in a similar direction, using a dictionary, but an array makes more sense. Ok, I'll do it that way.

Kind regards, Manu