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Ambient occlusion is really a wonderful thing for 3D work. What it lets you do is settle everything down. Here's what ambient occlusion is in a nut shell. At some point light is general and therefore ambient in the scene. It's not from anywhere in particular. Adjacent objects block that light. Giving us grounding darkness in the corners of walls and floors, or up at the ceiling where the ceiling meets the wall. Under characters feet and under furniture, it's that lingering darkness. Not a shadow, but simply darker than the rest of the room.
It's a terrific thing for grounding pieces. Making stuff look like it's in contact with whatever it's adjacent to. We'll add on Screen Space Ambient Occlusion as an image effect here, to help add some of that grounding darkness to our scene. I'll pick my main camera and I'll scroll down under my sun shafts and add a component. I'll choose Image Effects and Rendering and Screen Space Ambient Occlusion. I'll scroll down and we can see in here in the SSAO effect is that it's got a sample count and it's medium low or high.
A radius and this is in scene units, an occlusion intensity. How much darkness is there in a blur? There's also an occlusion attenuation and minimum Z. Finally, there's a shader, and a randomization within it. What this lets me do, in a nutshell, is put in the occlusion and say, how big is the spreading darkness in the corners? I'll start out with a radius at 0.5, and see how it looks. I'll put the sample count up to high, just to see if I can really see it. And also if I can pull it back down, and notice any difference.
I'll press Play and see how it behaves before I adjust it more. We can definitely see the ambient occclusion, it's the low darkness along the walls, really grounding them and making them look like they're contacting the floor. Up at the ceiling, it's a little bit on the dark side, and a little heavy, so I could probably pull that distance back. As I play forward though, it's a nice way of adding some gravity into the scene. It's definitely too heavy on the ceiling. It works really well on the walls, probably because down low they're darker any how.
But, in some places, it's a little bit too much. I'll get out of the preview, and check out the eclusion seeing if I can pull it back just a little bit while still maintaining that gravity in my scene. Here's what I'll do. I'll pull back the occlusion intensity to 0.8. Maybe that'll reduce the darkness just enough that I can get by here with a lower sample count. I'll drop the sample count to medium, and press Play again. This is better. I still have some darkness up here, but it's not nearly as, well, ferocious as before.
The walls are definitely grounded, and everything is definitely in contact with adjacent objects. I'll pull this back just a little bit more, as I don't want to counter act the white walls in my gallery. I'll pull the radius back to 0.35 and see how it looks. I'll also play with the occlusion attenuation. The rate of fall off in that occlusion I'll try this by pulling it up a little bit higher, to 1.5, so it falls off quicker. That's better. What I've got now, now that I've adjusted the occlusion, is some fairly tight grounding darkness in the corners, without being oppressively heavy.
I could even pull it back a little bit further, or just leave it alone for a good feeling of gloom in there. It's up to you how you would like it to look, but this is a great way to really add some gravity in the room. Keep in mind, though, that because it's a screen-space occlusion, and we've got limited quality available. That on small tight things like the Emma's feet for example. We're not going to get a ton of occlusion, they're also in a spotlight which is going to mute out most of the occlusion. And it's just a screen space effect, not actually a rendered occlusion like we'd use in 3DS Max or Maya.
If you do need occlusion in tight, dark areas such as the vents or outlet for example. Or maybe on a sculpture or other model where a normal map has been baked out. Render that occlusion out and composite it into the diffuse texture. This screen space occlusion is good only on geometry. And so a lot of times, because we're using textures to put in final detail. The screens' base occlusion will be kind of a general wash of darkness. More than a fine detailing and darkness popping things out. It looks pretty good.
And definitely helps kind of ground my scene. My gallery is really coming to life. And here's that car one more time. As I get close enough, it knocks into the other car and the two d-sprites drop down in their own physics.
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