Breaking down Embark Studios "Real-Time Hair" process

I came across this talk on Hair for AAA games on Blender Today, and I wanted to learn more. I also read the blog on Embark Studio’s website and watched Daniel Bystedt’s Blender Meetup talk. I understand it to some degree, but there are some things I’m not understanding.

I’m trying to create a mullet and from what I think I understand so far, I created this texture using a slanted plane, hair particles, and an orthographic camera.

HairCards

What I don’t understand

  • How to have a background when rendering the hair cards and still have an alpha channel (1:54)
  • The shader for the hair particle system looks like it’s made with a combine RGB node, but I don’t understand what the inputs are.
  • How to use the Particle Instance modifier > layers to randomize the hair card texture. My guess is plugging in an attribute node for “value” into a mapping node
  • How the material shader for the hair card is used to create controls

I was wondering if there is a full breakdown of this process that I haven’t found yet, or if somebody can explain what is being done, especially in the shaders.