I used the curve to mesh modifier to instance a square grid into a curve. I want to uniformly scale random segments of the resulting "tube" in the xy plane.

Capturing the indexes of the faces I use them to address a pair of faces (top and bottom of tube) to scale.

Index of top face = 4n-1

Index of bottom face = 4n-3

Entering numbers according to these functions manually works as expected: (n=55 in this example) enter image description here

Using nodes to calculate random numbers DOESNT NOT WORK. WHY? (only one of the two adressed faces is selected properly, the "counterpart" (face on the bottom of tube in example) is not adressed/in another place as expected for some reason enter image description here

  • $\begingroup$ Hello and welcome. Please don't write in all caps in the title or body of any posts, it is the written equivalent of shouting, is harder to read and may be [considered rude](en.w $\endgroup$ Commented Feb 29 at 0:02

1 Answer 1


The issue is because you have a random value per face index. That means different faces of the same ring may have a different random value.

You can divide the index by 4 (as 4 faces per ring), input that in a boolean random as ID so that all 4 faces of the same ring will have the same boolean value.

Then pick opposite faces which are odd or even (unmute the 'not' node eventually) depending on the opposite faces you want to scale.

enter image description here

  • 1
    $\begingroup$ +1 i had a solution as well - but it was not as elegant and clever as yours! $\endgroup$
    – Chris
    Commented Feb 29 at 8:59
  • $\begingroup$ @Chris, thanks to say that! $\endgroup$
    – lemon
    Commented Feb 29 at 9:12
  • $\begingroup$ @lemon Nice solution! thought the index node uses vertex indexes by default. what makes the index be the face index here? or is it just that their effect is identical in this case due to math shenanigens? that was the whole reason i wanted to capture the face indexes in the first place. $\endgroup$
    – sinwar
    Commented Feb 29 at 17:13
  • 1
    $\begingroup$ "Scale elements" is set to "face", that's why the index in the 'field' going among the node tree is also a face index. Saying it another way: index is the index of what we are talking about when it's used to transform a given geometry. $\endgroup$
    – lemon
    Commented Feb 29 at 17:15
  • $\begingroup$ @lemon they should really add a symbol to the index node to represent what kind of index it outputs. do you know where i can suggest that? especially since they literally added icons for vertex/edge/face for the measuring tape tool recently $\endgroup$
    – sinwar
    Commented Feb 29 at 17:30

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