Is a Directional/Flow Map Necessary for Hair Cards?

Question

I'm currently creating hair cards for my character and from what I've researched, it seems that I need to create the following hair cards for everything to look good:

(1 Diffuse/Albedo map

(2 Specular Map

(3 Normal Map

(4 Direction/Flow Map

(5 Opacity Map

(6 Ambient Occlusion

I understand how to create all the following in Blender and in Gimp (I want to stick to open source software for everything I create for my character) except for the direction/flow map. I read on other forums that creating a flow map may not be necessary if the UV's are all unwrapped and flowing in the same direction, is that correct? I'm planning on using Unity eventually and Unity has a Master hair shader I may be able to use and on their website, it has a hair strand direction section.

I started trying to create a directional map in Blender using this node setup but I'm not sure how to get the direction/flow colors correct (From the roots to the tip of the hair). Do I even need to create directional maps for my hair cards, and if I do, how can I create this using Blender or possibly another open-source program? Thanks in advance.

Answer 1

Stumbled on this while looking for a way to vector field flow in blender... While I'm here "I read on other forums that creating a flow map may not be necessary if the UV's are all unwrapped and flowing in the same direction, is that correct?" No. Absolutely not. If you bend the hair cards in your particle, it matters not where the UV goes, the flow of the normals is impacted and different engines (namely unreal) will render stuff differently.

What the flow map is, for hair cards, is a fixed world normal texture that covers each individual hair card. So you need to create an additional UV in blender, smart UV unwrap, and bake world normals. You can then play with the texture paint tool and some visual balancing to adjust the flow look manually - a bit tedius. Usually use the smudge tool.

The shader, is than told to use this map with UV coord 1 to derive normals and tangent. making the hair appear to bend more appropriately.