Basic single pass alpha blending always does a poor job for rendering hair. Blender gets away with it's alpha hashed blending, but nothing else supports that as it uses sampling overdraw to make it look good.
You could try setting it to opaque with alpha clipping, but that usually ends up look too chunky and thick.
Ideally you would need a multi-pass shader to render the hair that does some kind of opaque or depth pre-pass before rending the alpha blending on top of it. Babylon.js can do this in theory, but I've got no idea how to make it happen.
- Duplicating the hair mesh
- Make a copy of the hair material
- Separate the duplicated mesh by materials and delete any duplicate scalp section
- Set the original hair material to Alpha Blend
- Set the duplicate hair mesh to use the copied material and set that to Alpha Clipped with quite a high clip threshold (0.7+).
This in effect creates a 2 pass hair renderer. The opaque alpha clip material effectively resolves most of the z-sorting issues and the alpha blend material draws the remaining hair with transparency.
e.g: Just rendered with alpha blend:
Then with an opaque alpha clip mesh on top:
It's a little bit wasteful as it has to process the hair mesh twice, but it works at a pinch.
As most of the hair is rendered opaque, it actually renders a lot faster than with just Alpha blend.