How to select multiple vertices of one or more specific faces with geometry nodes topology nodes? (Blender 3.5)

Question

I'm trying to figure out how to use new topology nodes in Blender 3.5 (In beta at the time I'm writing).

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CASE 1 (it seems to work):

As a simple exercise, I want to put points on the nth vertex of a specific quad face. So I basically want to enter the index of the face that I want to select, and the index of one of the four corners that I want to select (to be later converted in vertices indices). I tried somtething like this, and as long as I want to select just one vertex on just one face, it seems to work:

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CASE 2 (something's wrong):

Let's say that now I want to manually select one specific face by index (just like the previous case), But now I want the first two vertices of that face. Let's say for example that I want the first two vertices of the 7th face, namely the one with index "6" and its first two vertices. In this case I want to select the index of the second corner of the selected face (index "1"), and use the "less or equal than" compare node, to finally select the first two corners. Something goes wrong:

As you can see, not only the 7th face and its first two vertices are selected, but the "less than or equal node" seem to have effect on the faces indices as well. So it selects the first two vertices of the first 7 faces, wich is not the desired result!

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Am I misunderstanding how these nodes are supposed to work? If it's the case, how do I get the desired result? Or Is it just a current limitation of what these nodes are capable of doing? Or maybe it is a bug and I should report it?

Thanks in advance!

Answer 1

If you want to select two specific vertices of a specific face, you would have to make the selection already in the Corners of Face node, because here it is decided which face corner should be selected.

With Sort Index you define which face corner should be selected. For a face with four vertices you can use any integer value between $0$ and $3$. If the value is higher, the counting starts again at $0$.

Afterwards you can get the index of the corresponding vertices by the so selected face corner with the node Vertex of Index. But then you have two values, which you have to compare with a little boolean logic.

Since you are in the attribute domain Points at this step, you can compare these values directly with the value of the input node Index.

_{(Blender 3.4+)}

PS: And don't worry, these nodes are already available in the stable version 3.4, so they are not beta anymore.