Controlling physical transparency - 3ds Max Tutorial

- [Instructor] In this chapter on ray tracing techniques, we'll start by looking at how transparency works in a physically based rendering. As we saw previously in the course, in a PBR, or a physically based rendering, there's no distinction between specular highlights and reflections. They're both controlled by the roughness. Likewise it is with transparency and refractions. In an old school first generation shading model, transparency and refractions are dealt with separately but in a physically based rendering, they're the same. I've constructed a test scene that works well for illustrating how transparency works. It's a very simple polyhedral object and it's got an image based lighting setup. I've placed an HDR file into the environment. Let's check in on our render setup. Go ahead and open that up, we want to be in target mode active shade. The active renderer is ART and we're going to render physical camera 001, let's lock that and we're just doing a 480 by 480 frame and our quality is 30 decibels. We'll do a render, okay there's our ideal diffuse material. Now we'll close the render setup dialogue, go into the material editor and create a new physical material found under materials, general, drag that over and then assign it to the object, drag from the output onto the polyhedral object in the view port and then double click on that material in order to load it in the parameter editor. Rename it glass. And we can choose a preset. There are three presets for transparent materials. Thin geometry is really only for single panes of glass. If I choose this, it will load here but as you can see, it's giving us no refractions and it's really unrealistic. Back up in our presets, let's go for solid geometry. And now we're seeing a blue tinted glass with an index of a fraction of 1.5. Let's change up that tinting. The transparency color has a slight blue. Click on that transparency color, set the saturation to zero and the value to one. It still looks blue but that's because the sky and the sea are blue in the environment. Click OK. Then we got the index of a fraction. It's setup for standard glass. If we want leaded glass, it'll be a little bit more dense. We'll set it to index of a fraction 1.7. By default, there is 100% transparency. We can dim that down a little bit and that will allow us to see a little bit of shading on the diffuse surface of the exterior of the glass. Set transparency to 0.9. And that actually dims down the brightness of the object and that's because the base color is black and so there's no diffuse component currently. We'll go into that base color and set it to a neutral value of 0.5. It's not going to subtract nor add very much to the color of the object. Value of .5, click OK and what we've done here now is given a little bit of diffuse shading to the object without changing its overall brightness. Let's talk about roughness now. Of course that's going to control the shininess of the exterior surface if we change it here. But there's also a roughness for transparency and that controls the focus or sharpness of the refractions. To make it clearer to see, I'm going to enable advanced mode up here and in the advanced reflectance parameters set a linear curve, give it a custom curve with a facing value of 0, an edge value of 1 and a slope of .55. And I'm doing that so that we will be able to see the difference between reflections and refractions very clearly in our test image. Down here, we see a reflection of the column or pedestal and up here, this is refractions through the glass object. We can control the roughness of each of those independently. Back up in our parameter editor, base color roughness and that's going to be just the orenayer blend shading that we saw earlier, it's going to just add a little bit extra side lighting but we're not really worried about that now. We're more concerned with reflection roughness and transparency roughness. Right now they're locked. When I change the reflection roughness, I'm also changing transparency. Let's set reflection roughness to 0.2. And both the reflections and the refractions are now blurry. Now let's try unlocking those two values. Under transparency, click the padlock. And now we have a separate transparency roughness which is defaulted to zero. And we can see now that our reflection is very soft but our refractions in the center here are very sharp. And we can of course reverse that relationship very easily. We can set the reflection roughness to zero so it will have a very shiny appearance on the surface. But then we can give it a little bit of transparency roughness, let's say .2 and the effect we achieve is a very highly polished piece of frosted glass. Let's look at this. We've got very sharp reflections but very soft refractions here in the center. And that's how to work with transparency and roughness in a physical material.