I've been trying to figure out how Parting Lines for Guides / Hair are supposed to work. But so far no luck, and the help files are just as cryptic as always.

When I draw a parting line on a Guide Groom or Hair, nothing happens and I can't find any input in te Hair or Groom where to adjust the setting or pipe in the Parting Line.

Does anyone know this is supposed to work ?

Thanks.

try using fabio, great tools for working the hair, most of the current tools comes form that tool set.

Thanks, I'll give it a shot.

Smells like not many peeps are grooming in Houdini.

I really hope the docs will be improved some sunny day, because most of the time they are completely useless.

Try to follow these steps:

Select the groom or hair you want to apply the parting line to.
Locate the Parting Line option in the grooming or hair tool settings.
Draw the parting line on the groom or hair by clicking and dragging on the surface of the mesh or curves.
Adjust the Parting Line settings as desired to fine-tune the look of the hair.

Hey thanks.

That’s what I’ve been trying dozens of times, but it has no effect whatsoever on the hair or the groom guides.

I suspect it’s broken in 19.5.534, or just not working in April ;-)

Did you try it yourself ?

Try to add a "rest" attribute on the parting lines (and possibly the guide curves) and see if that helps. You can do that easily with a rest SOP.

Meh, even adding a "rest" attribute doesn't seem to make any difference.

I'm not 100% sure, but I think the guides have to be "sculpted" in such a way that there's an actual parting line, like on a head with two pigtails for example. The guidepartition's curves then tell the generated hairs how to interpolate in the area where the guides diverge and would be otherwise confused as to what guide to folllow. Try this on a sphere with two pigtails to see whether you'll see a difference.

edit:
here, see this example

Aah, I see it now.

I was expecting a much more obvious effect on the guides or hair.

But like you say, it's a very subtle effect to be used on top of grooming the hair in a direction.

Muchos gracias, 10 bonus points for you ;-)

Thanks.

till today i am not happy with how the partline works, so just just break the hair in sections

pelos
till today i am not happy with how the partline works, so just just break the hair in sections

I try to feel your pain alas it might be more helpful if you'd give us an idea of how _you'd_ like the parting lines to work ... aka. what is your expectation on this particular feature ?

I am beginner in Houdini Grooming and would be grateful for an example of use of the Parting Lines. The toggle "Respect Parting Lines" promising "a brush will only affect guides on the cursor’s side of a parting line" on the Guide Groom SOP is really tempting. I was hoping, that if I start the stroke on one side of the parting line (or "inside" parting lines?), then the brush will not be affecting the guides on the other side of the Parting Line.

parting line has never worked as intended/expected, easier to just split the hair into sections. example 2 hairs, one left and right side for your example

@pelos thank you very much for the information, and for saving my time in vain attempts I will split it into sections, as you say

I think splitting your groom into sections is almost always a good idea and can help with parts, but the partition tool is still useful to know how to use and depending on what you want to do, can give you looks that are difficult to achieve with separate grooms.

The documentation isn't great on the tool, but I'm pretty sure that what is happening under the hood is that the partition tool is affecting the guide interpolation of the hairs. So it isn't meant to alter the guides themselves. If you apply it only to a guide groom alone, you won't notice much of a difference. It doesn't make an obvious part in the guides all by itself.

However, if you have guides that have been groomed with other tools to create a noticeable change in direction, normally when you add a hair generate node, it will try to interpolate through the change in direction as it adds hairs in between the guides. You'll get a part, but if your hairs are a lot denser than your guides they'll smooth out the part created by the change in direction of the guides.

The guide partition forces the hair generate to perform a more abrupt shift in direction as it interpolates through the guides across any lines of partition you create with the partition node, resulting in a more obvious part. Again, this won't be very noticeable in the guides, but once you generate hairs from them, it does create a noticeable affect.

Below I'm showing the resulting hair generate with and without the guide partition on the preceding guide groom.

It's not a perfect analogy, but I think of it like a crease line in hard surface rendering. Normally your renderer uses your normals to smoothly interpolate across what are, in reality, faceted polygons to create a smoothly curved surface. But if you add a crease line, the renderer knows to interpolate the normals across that line in such a way that you get a more abrupt change and an apparent sharper edge long that line.

Now can you split your groom? Absolutely. But now you've lost the ability to interpolate across the part. This can be a pain if you have areas where your part gradually fades out into an area without a part or with multiple parts (like as a part reaches the whorl).

Thank you very much Geoff. I attach my attempt to test the impact of the Parting Line. It works exactly as you described it!

Btw it is pity that we cannot use Guide Groom tools to affect Parting Lines. The Brush tool, the Sculpt tool... I have tried to temporarily disable the @group_partinglines, but then the parting line's "root" snaps to the surface (obviously).

Thanks again! Best regards.