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In this chapter I'll look at Ambient Occlusion and Specularity as a way to add realism and detail to a model. We can model high-res objects and use the occlusion from them on low-res pieces to look like they have more detail. In previous videos, I have painted in things like rust and dirt and wear, such as on the gas pump and tools. In this video, I'm going to take things like my shutter here and my Toolbox that's missing its handle and use the Ambient Occlusion as a foundation for dirt and rust. I'll do this in two different ways.
For the Toolbox I'm going to put a ground plane under it and render the occlusion into the UVs. What we will get there is black on the bottom, which is okay, but more importantly, occlusion that rises up the sides of this Toolbox in a place that we naturally see rust if this was left out. For the shutter I have modeled a high-res shutter, and while the poly count on this is ridiculous to use in a game, it provides a terrific high-res source to bake occlusion. I can then put that occlusion onto a low- res box, and it will look like that shutter.
When I combine that with a Specular and Normal Map, in addition to the color, it's really going to look like a very nicely detailed piece. I'll begin with the shutter and a quick discussion of what ambient occlusion is. I'll select the Toolbox and press Ctrl+H to Hide it. I'll pick my shutter and press F to zoom in. I'm going to put a new material on here, so I can show the occlusion looks like. We'll do this through the Batch Bake and mental ray usually, but I'd like to be able to show occlusion and the parameters before I get into that. I'm going to assign here a new material.
I'll put on a Surface Shader, and in that Surface Shader in the Out Color texture, I'll put in my occlusion, down under mental ray Textures is my mib_amb_occlusion. I'll pull up my IPR. I have turned on mental ray as a renderer and increased the antialiasing a bit, so it looks a little better. If you like to do this, you can go into the Render Settings into the Quality tab. Under Quality I have changed the Sampling mode from Adaptive to Custom, and put the samples from 0 to 1. This way every pixel gets at least one sample and at most four.
When I click and drag a region in IPR, it starts to render, and I get a pretty good look at my occlusion. What we are seeing here is that the Bright color, where there is no occlusion on an object is expressed as white. Dark colors, where bounced light is fully blocked by adjacent objects is black and between there is a gray. As on the slats here, we can see that there is some bounce light blocked, more importantly we can really tell that it makes the detail pop out. We get of very good idea of how this is going to look in shade. In occlusion, the main things to concern ourselves with are Samples.
The number of Samples is the quality setting. More samples means fewer dots in the occlusion. I'll put this up to 128, so it's really smooth. It will take a sec and refresh that IPR, and now my occlusion is smooth as it renders. I have also got a Max Distance and Spread. Max Distance is the distance apart at which objects stop occluding. A Max Distance of 0 is a special case, meaning that everybody participates. Objects no matter how far apart occlude each other.
This is good in some places, such as buildings against each other outside. But for things like the shutter, it may cast a gray in places I don't want. This is the reason to model things in real scale. In this way the Max Distance in seeing units lets me specify where the occlusion sits, either gently grounding objects, or adding a heavy gravity in the corners. I'll put my Max Distance up to 2 and see what the difference is. With the Max Distances at 2, my shutter looks clearer.
The edges, although they're aliasing somewhat, are brighter and whiter and the occlusion really just sits down in the corners of the slats here and up on the edges. This might be a better choice if I need a lighter looking render. I'm going to bring this back down to 1 and then get ready to bake this. As a quick experiment at 1, it feels like I'm losing too much of my occlusion, what I'm seeing here is that I'm losing so much of the detail where it goes all white. Now in a game, I'm going to bake this in a flat render, so I shouldn't lose too much, but I'd like to have a little more shading on the surface, as if this is set out and gotten dirty over time.
I'll bring this Max Distance back up and just kind of test out and see if it looks good. Now I'm ready to bake and here's how I'll make this work. I have demoed the occlusion using a Surface Shader, but really I'm going to take this and turn it back to lambert 1, I will render with ambient occlusion like that. That is what we use in movies. That's how we make things sit down in a scene and have characters ground. For a game we need to bake this occlusion. I'll right-click and assign my existing lambert 1 material.
What I'm going to do is to take a box of this exact size, unwrap it and then map half the shutter to get the occlusion bake correctly. I'll start out with a Poly Cube. I'm going to make a high poly and low poly shutter here. I'll draw my box in, and I remember the dimensions. This box started out at a Width of 18, Height of 36, and a Depth of 1.25. I'll hit Enter, and there's my new box.
I'm going to position this over the old one, selecting it and using my Align tool. I'll get it on the center by zooming in. With the occlusion low poly in place, I'm ready to bake. What I'll do in the next videos, then, is unwrap this low poly and set it up so the occlusion from the high bakes into the UV space of the low, adding more detail to what looks like a flat box.
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