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The Round Corners node is a special node that allows you to add the beveling on the edges of your surfaces at render time within the shader network. So a common problem with the rendering CG models is that the corners of the object or the edges tend to be perfectly sharp. So let's take a look at this cube right here. This is just an ordinary polygon cube and you can see how the edges are perfectly sharp, and that tends to make the object look very perfect in the renderer and thus it creates sort of an overly perfect or overly CG kind of look.
So the solution for a long time has been to actually just model beveled edges onto the surfaces of your objects. So I have a cube here. It's the same as the first one except I've gone in and I actually modeled and beveled edges on all the edges of the cube, and it's a fine solution. However, it can be very time consuming on complex objects and it adds an awful lot of geometry, and it limits your flexibility too, because there's no way to change the beveling after you've added it into the surface, at least not for very complex objects.
In mental ray there is a special node called the Round Corners node that is used to add the beveling in the shader network so they don't have to be modeled in by hand. Let's take a look at how to add this to a shader network. I am going to hide this cube because we don't need it at the moment and I'll bring this one over, and let's take a look at its shader. I have an mia_material shader applied to it and all I've done is I applied the Chrome Preset to the shader itself using the Preset options, Chrome, and then to make it a little bit easier to see in the render, I've lowered the Reflectivity to 0.5 and I've set the Glossiness in the Reflection section down to 0.35.
So do a quick render so you can see what this looks like. So here is our cube and you can see it's very perfect. The edges are absolutely 100% sharp. It tends to look very computer-generated. So I'll keep this image and now we'll add the Round Corners node. To do this, I am going to go down in the mia_material down to the Bump section, and you'll see that there are two slots for Bump. There is Overall Bump and Standard Bump. So the fact that we have two slots gives you a little bit more flexibility. You can use the Standard Bump node to put in textures, to create things like scratches and dents on the surface, using either file textures that you've painted or procedural textures.
So, it's just like the bump channel in Blinn or a Phong or a Lambert. The overall Bump slot is meant specifically for the Round Corners node, so that this means you are going to have a surface that has both round corners and some kind of bump textures at the same time. So, I am going to click on the Texture icon next to Overall Bump and under mental ray I am going to select Textures and I am just going to click on the mia_roundcorners button, and that adds the mia_roundcorners node to the shading network.
And it's a fairly simple node to work with. You just have to play with some of the parameters here. The main Parameter you want to mess with is the Radius. This sets the amount of beveling. I am going to start by setting this to a low value, something like 0.05, and see how that looks, and I've stored this render using the Keep image button and now I am going to do another render and we can compare. So you can see that without doing any extra modeling I have a nice round corner in here. If I store this image and then use the slider at the bottom of the render preview, I can compare the first image with the new one.
So there is the original image with the sharp corners and this is the new one with the round corners. So you can see how much it adds. It's just a little touch of realism to the surface and it can be subtle or it can be extreme. If we start to make this too high, of course the corners get very rounded and it starts to look a little bit strange. So you probably want to keep this at a fairly low value, although 0.1 seems to work pretty well. It's not too bad. If I start to bring this at values closer to 1, we get something like this. So then it starts to look a little bit strange. If you're going to do an extreme beveling or rounded edge, then you probably want to consider a solution that involves modeling, but for just a slight beveling, the Round Corners node works really well.
And there is a bump channel here, so if you're using this in a network with a shader that only has a single bump channel, something like a Blinn or a Phong or a Lambert or something that, you can add a second bump texture here within the Round Corners node and there you go.
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