Fluffy Tail Simulation Showcase With Custom Hair Geometry Nodes

"First: this is an actual proper simulation, not some fake GN 'offset previous frame' workaround people usually try to build with nodes, instead, we don't use nodes for simulation at all, but mesh.

What I did was: Duplicated the entire GN hair object, applied all modifiers, deleted most of the hairs but kept the guide curves, convert those guides into a mesh. Now these few mesh lines match the position of the guide curves in GN.

Now that it's a mesh, I could apply cloth sim, soft body sim, shape keys, and even rig it. Yes, rig with bones a GN hair system. You can easily make 100m hair, animate it with bones, then apply physics with pin groups. You can even export it, simulate it in Houdini or other software, then import it back.

Then I transferred the mesh position data back onto the GN hair, while neighboring hair follow the guide curves. That part was actually the easy one. Now comes the big boy problem.

Blender provides predefined GN hair modifiers like noise, clumping, etc. The default workflow looks something like this: Guide hair > Interpolate hair > Noise/Clump modifiers > Surface Deform. Surface Deform is the node that makes the hair stick to the deformed/animated mesh.

And THIS is where the major issue happens. Normally, all the math/noise/clump is done when the curves are using a static mesh.

Imagine a low-poly sphere with a single clumped hair strand. The clumping creates a sharp tip shape. Normally, before rendering, the sphere gets a Subdivision Surface modifier to smooth it. But the moment you smooth the mesh, the sharp hair clump disappears and becomes soft and rounded. You lose the sharp spikes of hair. Why?

Because Blender first generates the clumping shape (spike), THEN applies Surface Deform afterward. Once the mesh becomes smoother and rounder, the hair positions shift slightly to stick to the smoothed mesh, destroying the original clump shape.

The order of operations is fundamentally wrong. In the old particle system, the sharp clump shape stays intact regardless of mesh subdivision. So the obvious solution would be to move Surface Deform BEFORE noise and clumping.

Problem solved, right? NOPE.

All the default Blender GN hair nodes (clump, noise, etc.) were designed for static meshes. Once the geometry starts deforming, the nodes completely break. So yeah... I had to modify almost all the default Blender hair nodes so they could properly work on animated/deforming geometry. And since I'm not a super technical person, I first had to understand how all of Blender's vanilla hair nodes actually work internally before I could even begin modifying them. Which basically meant spending 3 straight months smashing my head against a wall trying to make this work."