I'm learning the GN hair node of B3.5 and I encountered a problem.

How does Clump Hair Curves use the original guide curves to generate clumps?

It always generates clumps based on Interpolate Hair Curvers, but I want it to work like particle hair, generating clumps with interpolation based on original guide curves.

I noticed that there is a guide Index in Clump Hair Curves, but I don't know how to use it.

Please forgive my ignorance of GN, looking forward to answer, thanks. enter image description here

  • $\begingroup$ Have you tried to connect the Guide Index output slot of the Interpolate Hair Curve node group to the Guide Index input of the Clump Hair Curves? When you use the node groups as modifiers then IHC stores these values also in the attribute named guide_curve_index that is internally used by the Clump Hair Curves when you tick the Existing Guide Map checkbox. $\endgroup$
    – Blunder
    Apr 23, 2023 at 14:11
  • $\begingroup$ Hi, Blunder. Thanks a lot for your reply, it didn't work but your reply made me retest the problem. I have found the problem and solved it smoothly. Cause of the problem: I'm using particle hair to create guide curves, in this process, the root of the guide curve is not well attached to the surface of the object (the key to the problem). After I converted the wrong particle hair to GN guide curve, using the Guide Index output of Interpolate Hair Curve, it didn't work properly. Thanks again for your reply, let me find the answer to my question, thanks. $\endgroup$
    – Seaway liu
    Apr 24, 2023 at 3:36

1 Answer 1


The Guide Index is an integer stored/sampled per spline, which is the index of the spline it clumps to. There is a boolean input on the clump hair curves nodes that is called Existing Guide Map; this input sets the Guide Index to automatically be the stored attribute in the interpolate hair curves node, which is the same as plugging the Guide Index output (of interpolate node) into the Guide Index input (of the clump node). The Guide Index generated by the interpolate hair curves node is the closest original/inputted curves to the interpolated/generated curves.

I hope this clarifies things.


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