About 4.0 and Particle Hair

[Maneki]

I saw a recent issue post about curve hair looking bad and particle hair is gone in 4.0 because the API doesn’t allow it. Particle hair sims aren’t always perfect but hair curves don’t really support comparable physics yet. As of now, if someone wants to use hair and simulate it, particle hair is the only way. Couldn’t you just script a automatic conversion from curve hair to particle hair in the hair tab, because a manual conversion works without any issues: https://blender.stackexchange.com/questions/279087/how-do-i-convert-hair-curves-to-hair-particle-system-on-a-mesh-so-i-can-export-i#:~:text=1 Answer&text=Select your hair curves%2C go,menu > convert > particle system.

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[Thomas Larsson]

Hm. I couldn’t get the convert tool to work. After having converted Toulouse hair to hair curves, I select the curve object and do Object > Convert > Particle system. Nothing happens, the hair is still a hair curves object and there is no error message.

[Maneki]

@Thomas Larsson Make sure you split hair and scalp into parts and when you try to convert curves into particle hair and select the curve hair before converting. It works for me.

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[Thomas Larsson]

It works on my home computer, but for some reason not at work. Anyway, what is a new tool supposed to do that the built-in tool doesn’t? Just repeating what can already be done with standard tools does not seem very useful to me.

[Maneki]

My request is to implement a one click solution to have hair particles as option on the hair tab again, this should be possible, no?

[Thomas Larsson]

OK, it makes sense, especially to give all particle systems reasonable settings. Implemented in last commit.

[Maneki]

It seems to work mostly fine, but no matter which viewport display amount I set, it’s set to 100 children. Also I get a error with certain hair. The error causes the scene not to load, I just get a empty folder named after the file. In this example I tested the G9 Alisse Dforce Hair:

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[Maneki]

Edit: Setting a custom segment count doesn’t work either, it’s always set to 5. Hair length is also always 4m, I’m not sure if the second one is intended.

[Thomas Larsson]

The number of viewport children is called “child_percent” in Blender 4, so I thought it was a percentage rather than the number. Fixed now. The segment count is set in Blender 3, but I suppose that Blender figures it out automatically from the hair curves in Blender 4. Anyway it is greyed out. The hair length is not relevant since we have the coordinates of each point on the strand.

The crash is more serious, since it happens in Blender 3 as well, even if I haven’t been able to trigger it myself. Fixed now, and I updated the release as well.

[Maneki]

As of now particle hair isn’t usable in 4.0. I couldn’t make any converted hair work so far. Either it immediatly explodes when trying to simulate or it doesn’t move at all (I assume because there’s a particle count of 0). On the following example the generated weight map is also really odd and no matter which hair I try or if I subdivide curves and then turn it into particle hair, it’s always segmented into 5.

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[Thomas Larsson]

It turned out that I could change the parameters from python even though they are greyed out. The particle count and number of segments is set to the same values as in Blender 3. The hair length wasn’t set in Blender 3 and I don’t think it matters, but it is now set to 0.5 meter which a more typical value than 4 m.

[Maneki]

Thank you, first tests show a significant improvement. There still seems to be some hair products which have partwise frozen strands but I think that’s just a issue with the dated particle system. I also did a test with dforce hair where every single strand moves and it doesn’t explode anymore. It also is now segmented correctly. (5 segments is too low for long hair) I’ll keep investigating.

[Thomas Larsson]

I added the hair length as a parameter too. I doubt that it matters, but it was easy to do and that parameter cannot be changed from the viewport.