How to prevent hair with geo nodes goes through mesh when using comb brush just like on second screenshot?
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$\begingroup$ Simon Thommes answered me There is a toggle in the top right $\endgroup$– NoobowskiMar 31, 2023 at 8:08
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As already mentioned in the comment there is the Sculpt Collision option. It's in the header area of the Sculpt mode. When enabled, it prevents you from combing under the surface.
However, this does not help if the hair is already under the surface. In this case, a Geometry Nodes (GN) modifier helps to bring the hair back to the surface.
Blender 3.5 already has a ready-made GN node tree in the Asset Browser. It's called Shrinkwrap Hair Curves.
Open the Asset Browser, go to the Hair > Deformation category, and drag & drop the icon onto the hair curves object in the viewport (not onto the plane/surface object!). A GN modifier is automatically added to the Curves object. This will bring the hair back to the surface. Adjust the settings of the modifier and when you are happy with the result you can apply the modifier.
For Blender 3.3 and 3.4 you can create your own Deflect From Surface / Shrink Wrap Curves modifier with some vector math:
Make sure you click the "shield" icon to set a fake user. This way, the modifier is saved with the blend file and not discarded after you applied it.
Enter the object Surface in the settings and change the Distance Scale and the Distance Threshold as you wish. If you increase the threshold value a lot, you will get the shrinking effect.
If you check the Include Roots box, and choose a negative Distance Scale and a low threshold, you can use the modifier to move the roots below the surface (for artistic reasons, to make the hair grow out of the skin).
