We've already discussed ambient occlusion for terrain and for objects, but we haven't yet discussed how it applies to characters. Ambient occlusion (AO for short) is a measure of how much light would reach each point on the model if it were surrounded by a spherical light source. Here's a picture of the unlit rabbit model with no texture, with just AO, and with both AO and color:
This technique highlights exposed surfaces and darkens recessed surfaces without enforcing a specific light direction, so it's appropriate to use as a basis for the color map. It's pretty confusing to start drawing the color map with nothing but a blank unwrapped sheet -- it's a lot easier to tell what's what when it has some basic shading 'baked' in. Here's the initial unwrapped texture sheet, followed by the baked AO, and then the final color map.
Ambient occlusion maps are not entirely physically accurate, but they do a great job of approximating detailed shadow effects that aren't yet possible to simulate in real-time. These detailed shadows aren't just eye candy -- they're important to understanding the spatial relationships of the model. For example, below are three more pictures of the rabbit: with no AO, with AO, and with both AO and color. This time it has the final shader effect so you can see how it all fits together. The left-most image has detailed surface features, but without the shadows it looks somewhat 'floaty' and confusing. The AO shadowing in the middle image makes the model look much more solid and real to me. With the masses already defined, the final coloring on the right brings the model to life, turning the stone into fur, rope and metal.
This is not an uncommon technique in modern games, but I thought some of you might like to see an inside look at one of the steps in the character creation process. This is just one step of many, which Aubrey has started detailing in his "How I make Overgrowth assets" series (so far we have the idea, concept, base model, and sculpting). Are there any aspects of model creation and rendering that you would especially like us to discuss here?(permalink)
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It would be cool to have a comparison between diffuse and diffuse + AO. These shots alone are quite amazing though.
I'm slightly confused though. Is the AO map integrated with the diffuse map, or is it a separate texture map, shader, or something else altogether?
Loving the informative posts.
Nice work, hell those UV map are a little hard to work, whatever the textures looks of good quality.
I love the informative, professionalism of the overgrowth articles. The images are amazing and clearly show what is being described. Would be nice to see some animations or possibly cloth modeling and the like :)
looks really nice!
These are gonna be some HQ player models! :D
What about phong and parallax mapping? Have you guys used those kinds of shaders?
I really can't see why they would ever want to use a phong on a character, unless you want him to look like a doom3 clayman. Parallax mapping also seems very unnecessary for this scenario.
Tell me more about claymen now.
Developer.valvesoftware.com
DooM 3 was just plain halfassed. No phong there.
Developer.valvesoftware.com
Everything becomes ugly when you use to much of it. Normal mapping also mecomes ugly when the strength is to high, same for parallax mapping, phong or any other shader or post processing effect like bloom, hdr, Depth of Field, Motion Blur... etc...
Parallax mapping is seriously overrated. There's virtually no point in using it.
Compared to normal mapping, it's significantly more expensive and in 90% of cases looks either indistinguishable or much worse due to the 'watery' effect it generates with certain types of texture.
More advanced techniques such as Relief mapping and Cone Step mapping are more expensive than parallax but look incredible. So just say no to parallax. If you're prepared to pay the performance cost, do it properly and use a technique which actually works.
Yeah, relief mapping looks awesome, although it makes you framerate drop somewhat. For lower end machines it would probably be too hard on the computer to actually be usable. I played one game which had relief mapping, don't remember which one it was though, dropped me quite a few frames, like 50 or something like that, compared to having them off, but it looked great. Normal mapping probably is the best solution for now, with todays hardware. Btw, I don't really know much about stuff like this though :/
parallax + round object = ugly
I've been patiently waiting for Overgrowth to come out for quite awhile now. I preordered it on impulse when the website first started offering them. Still excited for this game.
Any ETA yet (note, big emphasis on "estimate")?
Hmmm... the only place to preorder Overgrowth is directly from us and we offer weekly alpha builds. If you purchased it anywhere else, you got ripped off! Please contact me at jeff@wolfire.com
Impressive. Helps the detail really pop but at the same time make it blend in with the world better.
ZOMG!!! my pc will explode.. when i see this the 1st time i was thinking that i isn't gonna be with AO, models of awesome quality and bump maps and all that cool things... :_(
i must have to upgrade my old pc... :(
man those textures look epic. I wish I were better at organic objects- far more detail and lighting on those than static machine objects.
This game is looking amazing.
furry mod?
Beautiful artwork, but why is his mouth open?
Loving this more and more :).