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Lighting and Rendering with mental ray in Maya with Eric Keller shows how to master practical mental ray techniques for rendering models created in Maya. This course walks through the most efficient and innovative mental ray techniques, including direct versus indirect lighting methods, creating different types of shadows, using the new ShadowMap camera, and reusing shadow and final gathering maps. A chapter on optimizing render times and enhancing render quality is also included. Exercise files are included with the course.
The Render Pass Editor allows you to easily manage or render passes for each render layer. To access this interface, I can just go to Window > Render Editors > Render Settings. You'll notice that in the Render Settings I have Common, Passes, Features, Quality, Indirect Lighting, Options. So the interface for Passes is found under the Passes tab. So you will notice that at the top of the Render Settings window, I have a menu, and this has the render layers that I have already set up.
So let's go to the toy render layer. You will notice that I already have a couple of passes set up: a reflection pass and a specular pass. So let's take a look at how this is divided. If I am in the render layer toy, what's going on here in the Scene Passes area up here, and what's going on in the Associated Passes? This particular interface right here, this window is kind of like a bucket that holds all the available scene passes that I have already created. This down here, Associated Passes, lists those passes that are associated with this render layer, the toy render layer.
So in other words, if I switch back to the masterlayer, you are going to see now in the Scene Passes section I have reflection, reflection1, specular, specular1. If I switch to the toy layer, I get one reflection pass moves down here, as well as the specular one. So these are the passes associated with the toy layer, and if I switch to the chromeBall layer, you see it switches. Now we have reflection 1, and specular 1 because these are the passes associated with the chromeBall layer.
These are just additional layers that have been created for the scene. So let's start from a blank slate here, so we can see how we can use the editor to easily create, add, and move passes between various different render layers. So what I am going to do is I am going to switch back to the masterlayer here, and I am going to select each one of these layers, and these icons here are just an easy way to manage the layers. This one that has the clapboard with minus sign next to it, it says Delete selected render passes. So I am going to delete this specular pass by clicking on that, and I will delete these other three, as well.
So now, I don't have any render passes in my layer anymore. They have been removed. I can prove this by switching render layers; you see no more render passes. So let's switch to the toy layer. I'm going to add a new render pass to the toy layer using the Render Passes Editor interface. In this case, I will just click on the Create new render pass icon, and this brings up a list. In this list we see all of the preset render passes that are available to us.
It's very rare that you are going to use all of these. Mostly, you are just going to use three or four, depending on how complex you want to make your render passes. In this case, I am going to create a Shadow pass, and I am going to scroll up in here, and let's see. I will make an Ambient Occlusion pass. I am going to Ctrl+Shift on Ambient Occlusion. So I have both Shadow, and Ambient Occlusion selected, and I'm also going to click Camera Depth Remapped.
So I am going to create these three passes. So I will create them, and here they are. Now they appear in the Scene Passes area. So this means that they are available for any of the render layers in the scene. So what I like to do is I'd like to associate them with the toy layer. So I have toy selected here in Render layer. What I want to do is move these from up here to down here, to the Associated Passes section. So I'll just select Shadow and click on this little green check box right here, and this just moves this down here; same with that, and then AO stands for Ambient Occlusion, and I will select that.
If I wanted to move these out of the Associated Passes area, all I have to do is select them. I can actually Shift+Select all of them and click on this icon right here, and this is just going to move them back up here, which means that this render layer will no longer use any of those render passes. So let's just Shift+Select them again and move them back down. Now, what I can do is I want to make some changes in these associated render passes for the toy layer. So what I can do is the first thing I will do is I will double-click on depthRemapped.
By double-clicking on it, it actually opens up the depthRemapped render pass in the Attribute Editor. So this means that I can edit the settings. If I wanted to, I can actually change the type of render pass that it is. I could change this to Specular, Reflective, or whatever, but since I have already decided on Camera Depth, I will just leave that alone. I know from personal experience working with the depthRemapped render pass that the point of this pass is it's going to create a render pass based on the distance of the objects here from the camera, so the objects will be shaded.
The lighter parts of the objects will be closer to the camera, the darker parts of the object will be farther away, and this is a great type of render pass to use when you like to do things like Depth of Field effects in the composite after you have rendered the entire animation, or the entire image. Let's take a look at a render and see what happens when I actually render it, because actually all these associated passes, with the exception of shadow, both of these are going to have some problems. So I would like to show you what those problems are ahead of time. So I have got the toy layer selected, and I am just going to create a render here.
We will just see the regular toy by itself, and I am going to load the render pass. So if I load the shadow, I am guessing that this one will look just fine. Here is our shadow. Just remember that when you composite this, you may want to invert this so that this is dark. But if I load the depthRemapped pass, I am going to see a very dim image, almost black. In some cases, this might be completely black; in some cases, it might be completely white. So what's going on there? Well, the problem with this render pass is it's determining the depth - if I double-click on this to open up the Attribute Editor - is determining the depth based on these values.
The near clipping plane is the area close to the camera; the far clipping plane is the areas far away from the camera. So this is basically a thousand units away from the camera. So I need to lower this value in order to bring the back of the rendered frame closer, so that the range of depth- mapped values is more visible in the render pass. I will bring this down to 100, and click on this, and if I lower the render pass, now we are getting something that's a bit more usable.
So I will bring this down even more, maybe down to 50; cut it in half, and now when I load the render pass, you can see that this is a little bit easier, so you can see the different parts of the object. In this case, the darker parts of the object are closer to the camera, and the lighter parts are farther away. So I can continue to tune the way this render pass works by using the attributes here in the Attribute Editor.
If I take a look at the Ambient Occlusion pass, let's open up Render view again, and do File > Load Render Pass > AO, this is what I get. I get something that looks like an alpha. I am not seeing any Ambient Occlusion shadowing; this is actually even easier to fix, but it's an easy thing to forget. So in this case I just need to go to my Features tab, and under Features, there is an option here for Ambient Occlusion. If this isn't on, it's not going to render the ambient occlusion in the pass, and this is an easy thing to forget.
So make sure you turn that on. I'll do another render, so now if I go to File > Load Render Pass > AO, now I see my ambient occlusion, and it's working nicely. So I am going to go back to my Passes, I will double-click on AO for ambient occlusion, and this will bring up the attributes for this particular pass. So I can change things on here, for instance the number of channels, if I want to include an alpha channel, I'll set that to 4, basically the different settings.
I think one of the most useful areas, and this is new to Maya 2011, is the use Local A0 settings. If I turn this on, I can adjust the number of Rays, to adjust the quality. I can also change the Maximum Distance and the Spread. The Maximum Distance is going to determine how far mental ray looks in the scene to determine how dark to make the various areas of ambient occlusion. This is in scene units. So a scene unit in this particular scene is represented by the grid, so these squares right here.
So what I might do is I will probably set this to something like maybe for this particular monster model I'll set it to 2.000, and so on and so forth, and you can just continue to edit the way the ambient occlusion looks by turning on this option. Once again, I can go to the chromeBall. Now that I have edited the settings for these render passes, if I switch to the chromeBall render layer, you will see that these pop back up to the scene passes. Since I have already determined the settings for these passes, I can select them whichever ones I want - maybe all of them or just individual ones, click on this - and now associate those render passes with this render layer, as well.
So the nice thing about the Render Layer Editor is that once I have established how I want my render passes to work, I can mix and mash all I want. If I wanted a different type of ambient occlusion for this render layer, I could just create a new Ambient Occlusion pass, and notice that it says AO1. If I wanted to rename this, I could call this ballAO, or something like that, so I know that it goes with this render layer, and simply click on this icon to remove that ambient occlusion layer, select this, move that down, and click on this icon with the green check box to move the ballAO pass down to the Associated Passes.
Double-click on this to open its Attribute Editor, and now I can have completely different settings for this Ambient Occlusion pass than for this one. So this is what makes passes very convenient and easy to work with.
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