Hair Flatness Changes with Rotation!

So, my character has the flatness option of the children turned up to 0.6, so the hairs lie flat on her head. But, when I rotate the head mesh, the tilt of the hairs changes, so the hairs aren’t flat anymore. Is there a way to tell Blender what the tilt of the hairs should be?

Thanks for your help!

Hi Nate

I tried to reproduce your problem - Blender 2.72b - and could not find a situation where the flatness changed
Please can you post your .blend {even simplified} so it is possible to explore the rest of your setup

I think that the children/kink/wave/flatness has nothing to do with the way the hair lies against the topology
It is a factor in creating the waviness of the hair
I am guessing you combed the hair, and it is this that controls the strand position wrt the underlying topology

It looks from the images that the hair is not changing as the topology is changed, it is just that the light falls through the hair strands and shows the underlying topology
Maybe this is an effect of the default lighting in the 3dview and it will not appear under your own lighting setup
Possibly it is because of the distribution of the parent strands over the topology, it looks as though all the parents are emitted near the parting line, so perhaps a more even distribution of the parent hair will hide the underlying topology.

Best of luck


Thanks for your feedback. I’ve attached a simplified version of the .blend file, so you can look at the setup.
If you look at the hair from the side view, you can see that the hair lies flat on the scalp mesh. But then, if you rotate the mesh 90 degrees on the Z axis, and look from the front view, the hairs are now flat vertically instead of lying flat on the scalp.


Hair Flatness.blend (1.79 MB)

Hi Nate, I am away from laptop at the moment, when I get back to civilisation I will take a look!

Best regards


Hi Nate,

Just tried your blend and … wow … freaky!
I experimented with a minimal setup, only 3 parent hairs to observe the effect of the mesh rotation on the wave

Flatness is not a factor
It does not matter if it is 0 or 1 for the effect to be observable.
I tried changing various of the childen hair kink parameters and they do not change the effect at all!
Changing to interpolated children does not remove the effect.

What is inconsistent is the direction that is created in the children hair kink wave
For example if the wave is in the X axis before the base mesh is rotated about the Z axis, the wave direction does not rotate consistently.

This is a bug I think.

You could bypass this by either using a different style of variation in the children hair kink
Or not using children at all, and just having parent hairs.
Or changing all the hair to a mesh.

e.g. in this picture the wave is in the Y direction, the children hairs are flat along the X axis

Then I have rotated the mesh on the Z axis 90 degrees but the children hairs do not have the wave along the X axis

The view in the bottom left is the OpenGL render of the image just to check it was not a viewport artifact

Best of luck


Thanks for your help; I guess I’ll have to do a workaround.
Is there some place I could report this bug to get it fixed?

Hi Nate,

The blender site has a bug report and tracking page

Happy 2015 Blendering