Opacity and refraction in Arnold

From the course: Maya 2018 Essential Training

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  • Course details

    Learn to create high-quality 3D models and animations in Maya 2018. This course covers the core Maya skills—modeling, texturing, rendering, and animation—within a real-world, project-based workflow. The techniques you'll learn here translate equally well to film, motion graphics, game design, and animation.

    First explore the basics of the Maya interface, including selecting and manipulating objects, organizing scenes, and customizing the interface. Next, learn about polygonal modeling, creating and refining meshes, sculpting, and working with NURBS surfaces. Once you understand modeling, discover how to create and apply materials—adding color, texture, and reflectivity to your creations. Then integrate cameras, lighting, and effects into the rendering process, and leverage the new Arnold for Maya renderer. Last but not least, instructor George Maestri show how to add movement and life to your work with Maya's animation tools.


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  • Welcome

    - [Instructor] Now, when it comes to transparency, Arnold is a little bit unique in how it handles it. So, let's take a look at how to create opaque, transparent, and refractive surfaces in Arnold. So, here, I have a simple scene here and let's go ahead and just render this. So, I'm going to go into Arnold, RenderView, and then just turn on Run IPR. This should show us the sphere and the cylinder. So, I'm going to select the sphere and we're going to apply a new material to it. So, I want to make sure I'm in my rendering menus and then we're going to select Lighting/Shading, Assign New Material. I'm going to go into Arnold and let's find aiStandardSurface. Apply that. This should turn a different color. Let's take a look at the Attribute Editor for this. So, we'll make sure I have that sphere selected and let's go over to that aiStandardSurface2. Now, this is the surface for this particular object, so, if I wanted to, I could change the color and all that, but, really, what I want to do is I want to make it opaque and then I want to also dial in refractivity. Now, the first thing I want to do is show you how to make an object transparent, and that's under the Geometry tab we have in Opacity control. Now, if I turn this down, notice how it changes in the viewport, but it does not change in the render. Now, here's a little trick that's really important. We have to go over to the shape node for this object. So, here, it's pSphereShape1. If you scroll down, there should be an Arnold tab. So, I'm going to go ahead and roll that out and then there's a little button here that says Opaque. Watch what happens when I turn Opaque off. Boom, there we go. So, now I'm getting transparency. So, opacity or transparency is decided on a per object basis, so you need to make sure that this is clicked off for any object you want to have transparency. So, I'm going to go back over to my surface here and let's go back down to the Geometry tab here, and, as you can see, I can turn Opacity up or down. Now, in addition to this, we also have another rollout called Transmission, and this controls the refractivity of the surface. So, I'm going to turn my opacity somewhere around the middle here, so we can kind of see through this, but I really want to see how Transmission works. Now, Transmission works with two values here. We have Index of Refraction, which is actually in specularity, and then we have the Weight of Transmission. So, if I turn this transmission all the way up, notice what happens, we get refractivity in the surface. So, we're getting this blue object here refracting along the edge here. Now, we could see this a little bit better if I make this object completely opaque. If I turn Opacity all the way up, you can see this effect. Then, if we turn that up, it makes it very easy to see how Index of Refraction works. So, as Index of Refraction goes up, the position of this object moves around. So, as you can see, that I can actually get a quasi-transparent effect here, just by allowing the transmission of light through, and that's with an Index of Refraction less than one. Now, as soon as it goes above one, notice how this particular part of the object is actually opaque. But we can control that by going back down to Opacity here in the Geometry tab and dialing that down just a bit. So, the combination of these three are really how you're going to get your transparent and refractive effect. Opacity determines the overall transparency of the surface, Transmission controls how light passes through that surface, and then the Index of Refraction determines how much of that transmission is refracted. Now, all of this is dependent upon going over here to the shape node and making sure that we have Opaque toggled off. So, hopefully that gives you a little bit more insight in how to create transparent and refractive objects in Arnold.

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