Control advanced transparency effects.
- [Instructor] Let's apply transparency and refraction to this vase or vase and the water within it. For transparent or refractive materials using the Arnold Standard Surface we adjust the Transmission properties. So that objects can participate in transmission rays we must disable the Opaque attribute on the shape nodes of any transparent objects. All objects are considered opaque in Arnold unless we specifically disable opacity.
Select the vase and open its attributes with ctrl + a. In its mesh shape node open up the Arnold section and disable the Opaque attribute. And the same goes for the water object. To get to that use the Outliner and scroll to the bottom and select vaseWater and with that vaseWater object selected back in the Attribute Editor once again disable the Opaque attribute.
Now we'll actually be able to see the effects of Transmission attributes in the Arnold Standard Surface. Let's check in on our Render Settings. I'll close the Outliner, open up the Arnold RenderView, choose Arnold, Render, and also open up the Render Settings. In the Arnold Renderer tab open up the Ray Depth section. Let's figure out how many rays we need to render this shot with water inside a glass vase.
We need to render the object that's behind all of the refractive surfaces and each surface, whether it's an interior or exterior polygon, will count towards the Ray Depth required. For each solid object we'll have at least two surfaces, one that faces the camera and one that faces away. The water is a simple convex shape that only requires two rays, but the vase is hollow and the rays need to go through the near side and also through the far side of the vase.
Each one of those is a solid piece with a surface facing the camera and a surface facing away. For the vase we'll need four rays. And we also need one more ray just to reach the background itself. So two for the water, four for the vase or vase, and one ray needed for the background, and that's two plus four plus one for seven. And in the Ray Depth attributes the default Transmission depth is 8.
So that is sufficient and we can leave it there, however the Specular Ray Depth is only 1 bounce and that's not sufficient for highly reflective surfaces near one another, such as water and glass. Increase the Specular Ray Depth up to 4. And that's the minimum number to avoid dark areas on, for example, the surface of the water. Also, while we're here increase the Diffuse Ray Depth up to 5, so we'll get some bounce light.
And to make sure that all of those rays actually get calculated set a Total number of rays to 30. Now we shouldn't see any dark areas in the reflections or refractions. We can close the Render Settings dialog and let's assign a new material. In the viewport select the vase or vase, right-click, and from the marking menu choose Assign New Material. In the Assign New Material dialog go to Arnold, Shader, and click Surface.
And in here you'll see aiStandardSurface, click that. And now its assigned to the object. Let's rename it, we'll call it vase_aiStandardSurface. I'll get my Arnold RenderView back into view. And in the Attribute Editor we're looking at the attributes for our aiStandardSurface. Over here we have the Presets button and if that has an asterisk next to it that indicates that Presets exist for the currently selected node type.
Click and hold that Presets button and from the pop up menu choose Glass and Replace. And that sets up the Base and Specular attributes for clear glass. The Base Weight is 0, the Specular Weight is 1, Metalness is 0, and Roughness is 0 for a perfectly smooth surface.
The index of refraction is set to 1.5, which is the correct density for glass. Open up the Transmission section and at least in the current version of Maya that I'm using the Transmission attributes are not stored in the Preset. So be mindful applying Presets and always do a reality check on the attributes. Here we want to increase the Transmission Weight.
And if we brought that all the way up to a value of 1 it would be perfectly transparent. Let's get out our Crop Region tool to speed up the preview renders, click on Crop Region, and click around the glass object. We don't want it to be perfectly transparent, the glass will absorb some light. Bring the Transmission Weight down to a value of 0.97. Below that you'll see the Depth and Scatter attributes and those simulate dense transparent volumes, but for ordinary glass we don't need them.
And we're not tinting the glass this time, but we could if we clicked on Color and chose some color. All right, cool, set that back to default white. Okay, we've got the basic parameters for glass set up, let's also assign a water material to the water object. Once again, go to the Outliner and select vaseWater and right-click in the viewport and choose Assign New Material.
And once again, it's Arnold, Shader, Surface, aiStandardSurface. In the Attribute Editor rename it water_aiStandardSurface. Once again, go to the Presets, hold that down, and from the Presets choose Clear_Water, Replace. And we'll need to adjust the Preset once again, but this time the changes are relatively minor. The index of refraction is set to 1.333, which is correct for water.
The Roughness is set to .12, which seems a bit too high, so let's reduce that to .02. The Transmission Weight is set to the maximum of 1. And once again, water does absorb light, but it allows a little bit more light to pass through than glass does. Set the Transmission Weight to .98. And that value gives us a more accurate simulation of the way light is absorbed by water.
When Transmission Weight is less than one the Base Color and Weight are available. Let's reduce the Base Weight to 0. Finally, for an interesting frosted glass effect let's select the vase, I can do that in the Outliner or the viewport, select the vase, and in its material attributes, under Transmission, at the bottom is Extra Roughness. Let's increase that, we'll set that to a value of .2.
Take a look at that in the RenderView. And we're getting a frosted glass effect, but the shiny highlights on the outside of the glass are not affected. So this attribute is kind of non-physical. It's blurring the refractions, but it's not sufficient to give the effect of frosted glass, because the surface is still smooth. So to soften up that surface let's also increase the Specular Roughness here.
Set to 0.2 as well. And now we have a physically accurate frosted glass that has surface roughness as well as blurry refractions. And that's how to set the Transmission parameters of an Arnold Standard Surface for glass and water.
- Arnold rendering concepts
- Lighting with Maya and Arnold lights
- Controlling exposure
- Filtering light with Gobo
- Light attenuation with Decay
- Image-based lighting with Skydome
- Exterior daylight with Physical Sky
- Arnold Standard Surface material attributes
- Mapping material attributes
- Rendering refractions
- Mesh subdivision and displacement at render time
- Shading effects such as ambient occlusion and vertex color
- Camera effects such as fisheye and depth of field
- Animation image sequence rendering