hi,
Thanks for all the information. Bill Womacks videos are great but he is making non-PBR materials for Prepar3d using an older version of blender. Blender 2.01.0 MSFS plugin has several PBR texture map inputs. If I baked a AO map I'm not sure how would even apply it. Like I said I am very new at this and I may just be missing a very basic understanding of materials I appreciate your advice.
I think many people get confused about what Ambient Occlusion, AO Baking and the AO channel in the MSFS comp texture actually mean. So I´ll try to explain how I understand it, correct me if I´m wrong.
First of all, AO and AO Baking has nothing to do with PBR alone, AO Baking could be done long before rendering enginges or game engines supported PBR workflow. Take a look at the product pages of some old ORBX sceneries that were made for FSX, many of them mention baked AO as a feature, and we all know that FSX didn´t support PBR textures (in fact I believe no game engine at that time did). But what is Ambient occlusion at all and why or why not should you bake it into your textures? It depends on which game engine you are developing your models and textures for. Ambient occlusion means that an area that is "occluded" by a structure (let´s say a gabled roof that extends beyond the wall limit) will be darker than its surroundings EVEN IF THERE IS NO DIRECT LIGHT shining on it. If a direct light shone on our roof, the area below the roof would be in the shadow. But even without a direct light the area will still be slightly darker than the surrounding because the indirect, AMBIENT light that is reflected on surfaces everywhere (like the street, a neighbouring house, parked cars or whatever) is also occluded by the roof structure. The effect is much more subtle than the shadow cast by a direct light source but it is still noticable and because our eyes are used to this effect in the real world and models or objects in games that don´t have ambient occlusion rendered somehow will always look slightly unrealistic and "bland" because the impression of depth caused by AO is missing.
Now the next question is, do I need to bake AO into my textures? The answer is probably Yes if your models will be used in a game engine that DOES NOT support native, realtime AO rendering (like FSX) and No if you develop models for a game engine that DOES support AO rendering (like MSFS). If you bake AO into your textures and import the model into MSFS, the effect will most likely look exaggerated, because you have darker parts on your texture where you baked your AO and the MSFS engine will darken does areas even further by rendering additional realtime AO in that areas, because the rendering engine is unaware of your baked AO. You can sometimes see this on screenshots of sceneries that are obviously direct ports of older FSX or P3D sceneries where the developers used their old textures with the baked AO and just converted the model to MSFS. Something just doesn´t look right, the exaggerated differences in brightness gives the model a somehow cartoonish look, and that is something you want to avoid because the whole point of PBR is that materials should look as close to the real world as possible. The tutorial videos where Bill Womack recommends AO baking were made for creating P3D scenery (which also doesn´t support AO rendering in realtime) and I´m sure if Bill made a new tutorial series specifically for MSFS he would not recommend it.
As Christian already said, of course some people might turn off the AO rendering in MSFS for performance reasons, and those people might like a model with baked AO. But to be frank, those people will most likely be the minority and if you have to turn off AO rendering for performance reasons you´ll probably have to lower other settings like texture resolution or draw distance and then the overall visual quality will suffer and your baked AO will not be the major factor in this.
The next thing you asked was, if you bake AO how would you apply it? For this it´s important to understand the difference between the AO maps that Blender or Substance Painter bake based on the geometry of your model and the "micro-AO maps" that sometimes come with professionally made materials on sites like textures.com. When you hit "Bake" in Blender or "Bake mesh maps" in Substance painter, the rendering engine simulates ambient, indirect light being occluded by the mesh geometry of your model. You can then combine the baked AO map with your albedo map (albedo map means the true color information of your texture WITHOUT any influence of direct or indirect light) for example in photoshop, after that it´s not a real albedo map anymore because it contains color information influenced by light, but you could still use the texture as the albedo texture in your MSFS material settings along with your metal/comp texture and your normal map.
So now you might be wondering what the red channel of the comp texture is used for if the baked AO map can be combined into the albedo map. This is where I do things a little differently than some other developers who would suggest using your baked AO map from blender as the red channel. IMHO the red channel can be used for micro AO effects that are NOT caused by the actual geometry of your mesh but by "faked" geometry provided by your normal map. You´ll probably know that normal maps are a way of creating the illusion of depth; e.g in a rough stone wall where the crevices between the stones are a little deeper than the protruding stones itself. The normal map can create this effect without you having to actually model the real geometry of the stones. But the problem is that even those small crevices and protrusions in the wall would cause some amount of ambient occlusion between the stones in a real world stone wall, while the AO Baking can only take into account actual geometry. This is why professional materials often have their own AO maps, to simulate those micro-occlusions that can´t be created by AO-Baking. Here´s a screenshot of a PBR wall material on textures.com that shows what I mean:
On the bottom left of the screenshot you can see the AO map of the material. Now imagine you´d want to create a wall to be used in MSFS with this material and your model would be a simple 10 x1x0,5 m cube to represent the wall. Now you would apply the albedo map and normal map as usual, the roughness map goes into the green channel, the blue channel for metalness stays completely black because the stones are non-metallic, and the red channel would be the AO map shown in the screenshot. By this your wall would look more lifelike in MSFS even though their is no actual geometry that the rendering engine could use for rendering AO.
I hope this lengthy explanation can help you understand the basics of how AO works in different games or engines. Enjoy developing!
Cheers, Fabian
