How can I get sharp sharp edges for vertex groups to use with hair? I mean, without having to separate the mesh(will use shape keys later).
As mentioned in title of thread, vertex groups are weight groups.
You can’t have a strict distinction in weights because weight is fading on a face with vertices of an edge at weight = 1 and vertices of opposite edge with weight = 0.
You can accept that border of hair may be one face loop more than border of vertices group.
For the moment, you have to deal with same solution as in 2.79.
You can edit Hair Particle System and delete hair guides beyond wanted limit.
You can use particle textures to hide a part of hair beyond desired limit.
The basics of distribution of hair have not been refactored, yet, in 2.8.
We can imagine that will change. We probably could use face maps for that in future 2.8x releases.
But, for the moment, no change happened in that area.
You can use textures to configure the hair density with arbitrary resolution.
It is what I mean by writing that :
Technically, setting influence of density from a particle texture above a value of 1 gives unpredictable results.A particle texture is a black and white image. And every pixel with a value below one is an area where default particle density will be reduced.
A Weight group does work like that on particles density. When you use them, amount of particles stays the same inside the group but they are more numerous to be located near a vertex with a weight of 1.
Ah, okay. Sorry, thought it meant some other kind of limitation of the usefulness for the feature. Nevermind.