7.194: Hair Shrinks While Combing

[Zangk]

I ran across a strange bug or issue.

I was using the eyebrow and shrinkwrap lesson as my base to create eyelashes. Once everything was in order I began to try to apply Particle edit to it (after grouping its vertices, after weight painting, after mirror modifying it, after adding a particle emitter). When coming everything would “shrink”. They would flee from the comb rather than embracing it (the ungrateful hairs).

I found that when I combed up they would shorten, comb down the same thing, but out front they would extend:

1. Extended:
   
   
2. Up:
   
   
3. Down:
   
   

I thought that the issue was the mirror modifier because it was behaving strangely. All the hair particle information is jumping over to it rather than the original object, so I can only edit on that side rather than on the expected side. But when I removed it, tissues persisted.

I suspect that it might be the geometry somehow since my beard and head hair are still working fine.

Is there anything to be done?

[NP5]

Maybe hair and particles do not mirror.

They seem to curl as expected.

[Zangk]

I looked at my images a day later and say that they could be misperceived without the outline- here they are with the outline on:

down:

Up:

One drawn back for comparison:

For comparison

But regardless, I monkeyed around with the system, taking into consideration that these hairs become shorter when up or down and found something of a reasonable length. This was done via cutting and maneuvering until I happen to come across a length suitable enough.

This does not solve the shortening of the hairs, but it does solve the aesthetics of what I was going for. Perhaps it was the geometry somehow?

@NP5

Maybe hair and particles do not mirror.

They do seem to mirror, but the system does not seem to know how to do so. For when I do make the changes I do want, THEN apply mirror, although it looks messed up, once I apply it , the particle system comes through almost exact (but not because of the random parts of that modifier). Until then it seems that blender does not know how to work with the particle system or the particle edit well. At least in this very specific case of "What in the world?.

Using your picture as a start, I recreated a flat plane with no special added geometry and tried to get the slight curl you have shown- to no success:

HairParticleIssue

Note that I am using Comb the entire time, not cut. Sometimes I zoom in to show that the hairs became short.

[NP5]

No idea how you can shorten hairs like that. (in video) They don’t do it for me. I can’t even get the rendered hair to show in particle edit. Hair is horrible. Eevee a nightmare if even trying to use the thing. They are working on a replacement, one can only hope they actually make it so it is controllable and works like a normal human being would want and expect!
It would not mirror for me in my experiment.

Others here have had more success with it, maybe they can help?

[ZachDude]

What about the size of the geometry? Maybe it’s too small to work properly? Idk just a shot in the dark since I’ve had similar issues working on eyebrows in Maya.

[Zangk]

This is what I am wondering.

I tried a huge flat square, subdivided it as well, and no problem.

Perhaps this is what I can chalk it up to.

[ZachDude]

It’s a working theory…

[Zangk]

Consider it Solved.

I will conclude, rightly or wrongly: Just like how the size of the object will effect the light, doing strange things if the object is too small. So I think that the size of an object can effect the hair particle system. I do not have any details, but it can be something people can keep an eye on.