In the next few lessons we want to take a look at the World Object. Now, we've seen the World Object a couple times before, especially when we're setting up glow elements. But now I want to open up the World Object and look through it tab by tab. The point of having a World Object is that you can have effects that are applied throughout the scene without having to define them on a case-by case or model-by model basis. So everything that's inside the World Input Window has the potential of being used by every object within your scene. The first tab we have is Fog-Ambient-Background. These are actually three effects that we'll look at one by one. The first one that we'll take a look at is Fog. In our scene we have a few cylinders and a ground plane. Let's go ahead and render a snapshot, see what it looks like without any fog. OK. Now, if we click Enable Fog, then what it's going to do is add a black fog because that's the color of the fog that's being applied to it and the Fog to Mode is set to Color. And the black fog has filled the image. Well, why did it do that? Well, there's something else that we need to set and that is filling the fog radius with the camera and I'll move these out of the way so we can see the top view in the camera and let's open up the Camera Object and in its window, click on the option to Show Fog. Well, now that we've done that we can close the Camera Info Window and back to the World Info Window. Down here where it says Radius, the radius is zero to zero. So it's filling the entire frame. And what we want to do is create a fog effect that starts at one point and spreads to another point in 3D space, sort of like a 3D gradient and for that reason I have the rulers being shown. So from the top you are about to see elements that describe where the fog is. So let's change the radius. We'll leave the start point at zero and the fog stretches all the way to, let's say, 2500 units. Now we see a disk in the top view that indicates where the fog reaches to. Now let's render again. Now we have our cylinders back but it looks like it's just getting darker back there. So let's change the color. Let's change it to a light blue and render again. Now we see the fog stretching back and getting thicker to where it's a hundred percent opaque. Let's change the radius again and this time instead of starting at zero, let's have it start at 1500 units and we see the camera being changed again and let's render another snapshot. Now we have a much more compressed area where the fog effect occurs and we can see in the top view these two disks indicate where the fog appears in our world. Let's change it back to a smaller number to begin with, let's say 500 and this time we'll have it fog to a closer distance so that the outside radius of the fog is closer to the camera than the furthest column. That's about 1900. Let's take a closer look at our top view. So we can see that the fog starts at 500, expands out in all directions in a circle but the limits are indicated by these disks because that's what the camera sees. So 500 units all the way to 1900 units and you can see from the camera view this last cylinder appears to be completely covered by fog. And that's what our snapshot shows also. Let's take a look at the controls a little more closely. There's a graph here that indicates the progression of the fog between the two radii. I can change the start amount, let's say it starts at 0.2 and extends to 0.8 and the graph reflects that. But I also can change the mode. So instead of linear, we can choose an Exponential Curve or these two other non-linear options. Real fog is closer to this exponential curve, so let's try that. Now we have a tiny bit of fog, again the amount is 0.2 extending to an amount of 0.8 at our furthest distance. Let's close that. Let's change the amounts back to zero all the way to one or zero percent to a hundred percent and let's take a look at this pop-up; Fog to Color, which is what we've been using so far. Let's change that Fog to Alpha and see what that looks like. Now, there doesn't appear to be any difference here in the RGB render. Let's take a look at the alpha channel. You can see that the fog appears in the alpha channel where the objects that are close to camera are a hundred percent opaque, fading out to a hundred percent transparency. So this is one way, if you're compositing your scene in After Effects or another compositing program, that you could create some depth effect.
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