nHair Problems - Why do the nurbs curves leave Follicles?

#1

I’ve been experimenting with nHair in Maya 2013 and I noticed that when you first set up nHair to a scalp mesh object and go to nHair > display Start position. You can clearly see the NURBS curves are attached to the follicles on the scalp, but the minute you run a simulation to get the hair into a natural position so that you can style the hair by editing the NURBS curves ie: nHair > Set Start Position > From Current. You will notice that when you go back to Frame 1, the Nurbs curves have become detached from each of their follicles. Leaving a small but very noticeable space between the curves and the follicles. This is a total disaster if you want to animate your character and do some close ups, lets say with a character that has a tied up hairstyle like a Ponytail. You can see clearly that the hair is not tight to the scalp.

So I tried to sort this out in Maya 2015 and the problem is still the same? Is this a bug? Why didn’t they fix it? I found a related thread for this issue here, but I never worked for me.

"1. select all follicles
2. in channel box set pointLock to noAttach (affects entire selection)
3. nHair:convert selection: to start curve end cvs.
4. hit down arrow (moves to first cv selection)
5. shift select surface(nCloth output mesh)
6. nConstraint: point to surface

If you need the bend stiffness at the attachment you can create a second point to surface constraint for the second cvs. Just follow the above steps again (minus step 2) and instead hit the down arrow twice.

In testing this I did notice a problem… you need to rewind twice to get a good start state. There is still a dg loop because of the follicle connections to the cloth, so you might need to hit rewind twice before caching as a workaround."

In fact when I tried this in Maya 2015 the Hair falls off the curves when you run the simulation, but in Maya 2013 it kinda works on the side of the head but not the top, like the forehead.

Does anyone have any tips on solving this problem as I’m losing my mind with this nHair stuff?

Thanks.

#2

I’m not able to reproduce your problem. There are a lot of different ways of setting up a hair system, though. Do you have simple reproducible steps?

I think in that old thread they had a problem with assignment of nucleus nodes, or some such issue.
However I do remember a problem where collision with the surface could push out the first vertex of the hair, but we disabled collisions from the first vertices to fix that ages ago

(note that if you simply loaded a scene from the older file into 2015 that already had the bad initial state it would not fix it… you would need to run simulation on the scene with the good starting position and set initial state again).

#3

the pop off because of trapcheck on the collider
.

#4

Thanks for the reply Duncan. I’m going to try to reproduce the steps I took in creating the hair and then send on the file and some screenshots.

#5

I didn’t know what you meant there Castius but I found what you were talking about in the Attributes Editor when I selected my passive Collider object (my characters skin) and in the nRigidShape menu I opened up the Quality Settings, the 5th rollout down from Collisions. “Trapped check”. I unchecked the box for Trapped Check and now the hair stays close to the scalp without popping off from it when I run the simulations! Fantastic!

Thanks for your help :thumbsup: :slight_smile:

#6

Now the bad news. There will be times you want trap check for better collision. So if you can split the collider from the emitter. So you can only turn off trap check where the follicles attaches. That will be best.

Until they fix this problem.