Procedural Hair Nodes

@Koen Vissers There is an operator for both directions of conversion. Just search for convert to particle system. You have to make sure that every modifier is applied.

@Bob Klassen There is an option in the trim node to do that instead

@Michael Vaughan yes, you can. Just make sure that you're not using the existing guide map but generating a new one for each clump layer.

@Simon Thommes Thank you for the fast reply. When you say generate a new guide map is that just unticking the 'Existing Guide Map' box, or should the create guide index map be use as well?

@Michael Vaughan It mainly means unticking the box, yes. Then you can use the settings to generate the guide map on the fly before that setting. Otherwise you can also use the create guide index map node instead to have more explicit control over the created guide map.

The fact that there are multiple inputs for the same thing next to each other and it being a bit unclear, which one overrides the other is an unfortunate result of this being implemented as regular nodegroups, which are more limited in how the inputs are presented. That will be improved in the future. I still need to write the documentation to clear this up more.

@Simon Thommes Thanks Simon. I have one more question, would it be possible to part hair Interpolate curves by mask or vertex groups instead of mesh islands?

@Michael Vaughan The parting could be done several different ways, that can in theory already be supported with the Group ID input of the Interpolate Curves node. The main issue is that there is currently no good way of combining multiple options like that in a single node-group and I couldn't make the setup modular in a good way either, so I went with the simplest solution of mesh islands. In the future node-groups will get more options of customizing the functionality and UI, then we can include more options by default.

For now, I'd recommend using a surface mesh that is separate from you're head mesh and either actually separating the mesh islands or using an edge attribute like the crease to split the mesh with procedurally.

@Simon Thommes Thanks again Simon. Is there a recommended step for parting hair clumps? The Islands work well for the interpolated hair, but it seems difficult to get a clean part when adding the clumps. I was trying with the Guide mask and Group ID.

@Michael Vaughan Parting is one of the things that are still a bit limited in their support in the first version. We need more flexibility in node UI to support more options there.

If you are using the existing guide mapping from the parted interpolation that should work by default for clumping. The Group ID input should work for custom cases. A few days ago I pushed a fix for that. Make sure you are on the latest version.

The easiest solution here might be to just use a separate hair object for the different parts though to keep them isolated.

@Simon Thommes Is there a way to add a few extra points at the root of the original hair curves?

@Michael Vaughan To add points you need to resample the curves. To extend the curves at the root you can use the Trim Hair Curves node and set the Pin at Parameter value to 1, to pin it at the tip.

@Simon Thommes For a stylized groom with around 100 curves, can you recommend a way to control the curves using a handful of bones? Is there a way to keep the shape of the groom and have a basic rigged mesh influence the location of the curve points?

@Michael Vaughan The that animation/dynamics work is still very much unpolished/missing. At least in regards to out-of-the-box tools. Because everything is based on Geometry Nodes you can take full control over the shape of the curves with those. The easiest way to control the hair with mesh, would be probably to create a duplicate of the hair that you convert to mesh, deform that with bones and then transfer the position attribute back onto the curves using the sample index node.

@Simon Thommes Is it possible to have curves that have been converted to mesh avoid self intersecting? In this case, the radius is larger than realistic hair so the intersecting is quite noticeable.

@Michael Vaughan There is no built-in method to solve self intersection. Anything is theoretically possible to build yourself with the existing nodes. But if you are at a level where self intersection is noticeable enough to be an issue, it might be worth applying modifiers and fixing individual cases by hand.

@Hibiscus Digital Media Yes, you have to use the surface_uv_coordinate attribute to sample the texture. You can do that in the hair shader or in the geometry nodes tree. In geometry nodes you can also use the Surface UV output of the Curve Info node. That is the same.

@Simon Thommes Thanks a lot. Let me try

@Wayne Batchelor For rendering with Eevee it depends a lot on you VRAM as well, rather than your RAM. Besides the amount of curves you also want to keep the amount of control points low. I don't have any rule of thumb for you on that though. But generally both Cycles are more efficient rendering curves directly than generating the equivalent mesh and rendering that.

@Simon Thommes Thanks, I'm always real conscious, maybe too much, of how much work I'm throwing at a processor, no matter how much I have.

@Simon Thommes  - Also, I've been using Duplicate modifier almost exclusively. It seems you have more control and less hoops to jump through on a stylized human character. Weight painting and extra scalp meshes seem extra steps to add to the processing stack. I know it may (or may not) be much but, I don't know which straw is going to break the camels back.