PBM
PBM is a subdivision of PBR That describes materials reflectance at certain angles. This covers how light hits and shades the material and how the light bounces off the material. We have options in the shader for nearly every major BRDF including SGGX for specular and Oren Nayar for diffuse. These options will dramatically change the way your surfaces look in the shader so have fun tweaking them.
Creating materials is fairly simple if you have the right tools, we recommend bitmap2material and the latest photoshop for editing and creating maps for your materials, there are 2 main textures you will need in pbr, that is the normal and the smoothness map (Inverted roughness). With these two basic maps we can calculate all the lighting information needed, however giving an F0 value will greatly increase realism and will allow you to render things such as metals. F0 describes the amount of reflected light when looking straight at a material with the sun directly behind you. Generally speaking most things land within the 0.02-0.05 range with metals in the 0.8-0.99 range, some materials can fall out of this range. You can control F0 per pixel so you can blend and mix things as you want.
Example of F0
The texture layout is as follows (Note some features are not implemented and may change in the future):
- RGB: This is your default normal values generated from your software
- A/Opacity: This is your height channel used for things like parallax mapping .png files have no alpha however they do have opacity.
- R: is smoothness also known as roughness, values lye between 0.0001 - 0.9999
- G: F0 values lie between 0.0 - 1.0
- B: Emmisive, this channel will allow you to make something luminescent
- A: This is still undecided, it will probably and up being Sub Surface amount for SSS materials such as plants, gels, and skin.
This is The basics to a Physical Model.
N dot L is the diffuse term.
Specular BRDF's generally look like this
All pictures credit to here: http://simonstechblog.blogspot.com/2011/12/microfacet-brdf.html