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(Using Blender 3.3)

Since particles seem to be deprecated, I am trying to use hair curves to allow me to precisely position instances on a model. (Consider feathers, as an example.) Specifically, want to position an instance at the root of each hair, using the hair's orientation and size.

Right now, I have: Group Input -> Curves to Point -> Instance on Points -> Group Output

This works fine for position and orientation, but I can't figure out how to correctly map from the length of individual hairs to per-instance scale.

I'm testing with a single hair, 0.1m long. Both Spline Length and Spline Parameter are giving different results compared to plugging in 0.1 as a constant scale. (As far as I can tell, both are in fact producing 0.) Curve Length seems to give the correct result, but of course that's only useful if I have exactly one hair.

How can I get the length of individual hairs in a way that I can plug into instance scaling?

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  • $\begingroup$ Please add a screenshot of your node tree, or better, share your blend file with us: blend-exchange.com $\endgroup$
    – quellenform ♦
    Commented May 28, 2023 at 7:54

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Since you don't want to share your blend file and don't provide a simplified example, I can only make assumptions...

To use the length of a spline when instantiating objects, while using Curve to Points, you would have to capture the spline length with Capture Attribute beforehand, and then use this value for scaling, because as soon as you have converted the curve into points, there is no value for a spline length anymore:

enter image description here

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  • $\begingroup$ What the actual... I'm going to have to try this again in my real model (I already tried exactly this, IIRC). Apparently, not only does 'grow hair' not work when the geometry node is applied (not entirely shocking), it also doesn't work on 2-point hairs, at all, unless "scale uniform" is enabled. 😒 It's possible that "quirk" is solely responsible for not figuring this out myself... $\endgroup$
    – Matthew
    Commented May 28, 2023 at 14:29

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