Tutorial: Creating proper PBR materials Pt1: PBR Definition

WORDY NERD WARNING
If you don't care about the tech nerd words, I suggest jumping down to 'The transition pitfall'


PRELUDE: Who am I exactly?
(Feel free to skip if you don't care lol)​

I Figure a good start would be explaining exactly why you should listen to this random guy spouting facts about rendering. I go by Zack most places, including the discord where I am quite active, and for some of y'all that will be enough. For the rest, I have worked on mods like the AN-12 and the Cessplane L19. That is is my public modding experience here. In terms of rendering, as of 2021 I have a Bachelors degree in Fine Arts with a 3D generalist specialization. To get that I graduated from one of the top Film/Game schools in the world, Gnomon. During my time there I had the honor to be trained in everything from hard-surface to game creation, each one of the teachers had some amazing titles under their belt. I got to learn from the best, and that is why Gnomon is a first pick school for many companies, and I got my training from there.

How is PBR different from the previous Specular system?​

Physically based rendering (pbr) can be quickly summed up as different parts of rendering that increase accuracy to real materials, being brought into one overall method of material rendering. Previously with BeamNG we had a specular system with a lack of gloss mapping (we had a slider but thats it). Specular was used to say how much a material would reflect:

High specular values = reflects a lot
Low specular values = reflects little/none​

These maps, in some render engines other than BeamNG, can have color to mimic colored reflections of metals. That would be combined with gloss, a value saying how scattered the reflected light is:

High gloss values = very clear reflections (ex: mirrors)
Low gloss values = very soft or almost nonexistent reflections (ex: concrete)​

You also had the easily recognizable Diffuse map, the map that had the color of the material. Usually just a picture or a generated texture of some kind.

(Source: PBR Texture Conversion)​

These methods were cheap for rendering and could be used to make really realistic scenes, but they had issues. You could have materials reflect more light than they got, and they usually had to be more tailored for a scene to look good, being the 2 biggest issues.
The fix? PBR Rendering! PBR does away with those two maps and leaves us with Roughness and Metalness (plus IOR in some engines, but we wont go over that). Roughness is the exact same as gloss, just flipped around. Metalness tells the render engine how metallic a part is, pretty straight forward. But why do we need to know if something is metallic? Metals reflect quite differently from normal materials, tending to be a lot more reflective and being able to reflect more 'energy' than non-metals. Diffuse is replaced with Albedo, basically a Diffuse map but it has 0 lighting information in it. It is just the raw color of the object.

(Image Source: Physically-Based Rendering, And You Can Too!)​

PBR also brings something called Fresnel. If you look at an object (I actually suggest you do this if you are curious) head on, it tends to be a lot more rough/matte then if you look at it from a harsh angle, this is Fresnel. Things get more reflective at glancing angles.

(Source: Understanding the Fresnel effect)​

All of this (plus a lot more technical stuff) comes together for one reason: Energy Conservation. In simple terms, you cant have more light come out then went in.

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The transition pitfall​

You may now wonder... why I am taking time to write all this out. I have noticed an issue with PBR mods, a lot are not proper PBR. Im sure that is confusing to hear, but the biggest mistake is treating PBR and the old method the exact same.

PBR has 3 rules:
NO lighting in the Albdeo. No AO, no reflections, nothing.
Materials are either metallic or they are not. There is no 'half metals' in most use cases.
No black/white Albedo. Max value: 240/249 Min value: 30/50. (Normal/Strict)​

What happens if you break one of those rules? It is not physically based anymore, this wont straight up break everything, but you are now in the 'tailored materials' territory. That is also why you should care. One of the amazing features of PBR is proper materials will look accurate in any lighting. Your car will look as correct in the snowy automation hills as it does in the dunes of a desert, because its behaving exactly as the material would. It is physically accurate, which means it will keep your car/map/whatever looking the best no mater how the lighting changes. Now, like in all art these rules can be broken in some cases, but you need to know exactly what it is doing and understand the effect it will have.


And that, is the (hopefully) first part. If the forums liked this information I can do a part 2 on verifying if something actually is PBR, and maybe even some basic texturing methods in Substance Painter.
If you have any questions, please ask and I will gladly answer them.

 

+1 for a part 2. I think I make okay materials, but it's basically just done by eye. If you're not aware, Materialize is free and allows generation of all the necessary PBR textures. Might be helpful in a tutorial sense for people that don't have pricy programs.