Learn about opacity and specularity in Arnold.
- [Narrator] To render a liquid mesh in Arnold, use the AI standard surface material. There are a few other settings that we need to change in order to render transparent materials. In my scene I've got three versions of the liquid. Here's the liquid layer on which we find the original particles. We're not rendering that now. If we try to, we'll get an error message. So let's turn the visibility off for that liquid layer. We have the mesh layer but it's disabled because we also have a mesh cache layer.
That's what we're working with. Leave visibility on for that liquid mesh cache layer and set the current time to frame 120, which is a representative frame. That might take a moment to load the mesh cache in. Select the mesh in the view port and open up the attribute editor to the mesh shape node. Open the Arnold section. Very importantly, disable the opaque attribute. The opaque attribute is enabled by default as an optimization for the ray trace engine.
If you want to render transparent or refractive materials in Arnold, then you need to disable opaque on each object. Additionally, we need to check in on the render settings. Open up render settings and go to the Anrold renderer tab. Open up the ray depth section. This controls the number of bounces or the number of times light can pass through a surface. That's the case for the transmission rays that has to do with refractions.
The default value of eight is enough to allow rays to go through all of the surfaces of this liquid. The default number of specular rays is only one, which is not enough to allow the light to bounce around on the surface. That means we will get some dark spots in the rendering. Increase the specular rays up to four. Also, while we're here, we should increase the number of diffuse rays up to five in order to provide some bounce light and improve the exposure of the shot overall.
Those are the render settings. We can go ahead and close that. We have a material assigned currently which is an ideal diffuse. Let's reassign the default liquid material. It's still in the hyper shade. With the object still selected, right click, and from the marking menu choose assign existing material. At the top of the list you should see something that looks like AI standard surface one. It might have a different number, but that is the material that got assigned to the mesh when we originally created the liquid emitter.
Release the mouse and assign that material to the object. In the attribute editor we can use the arrows to page the tabs over to the right, and select AI standard surface one. Those are the default material properties for a Bifrost Liquid mesh. Let's see what that looks like. We'll do a draft-quality rendering. From the rendering menu set, go to the Arnold menu and choose render.
When that draft-quality rendering has completed, let's store it as a snapshot in the Arnold render view. Click on the little camera icon. Now we can compare this default material to one that I have prepared. The default one shows that transmission is working. I have a backlight outside and transmission is actually coming through, but the overall fluid looks very dark. I've got a material that uses much more conservative settings for the color of transmission, and I've also added some subsurface scattering.
Let's assign that. With the object selected, right click in the view port. From the marking menu, choose assign existing material. You're looking for seaWater_aiStSF or AI standard surface. Release the mouse. That's assigned. The Arnold render view should update automatically. If it doesn't, you can press stop and restart the rendering. With that second rendering completed, let's also make a snapshot of that.
We can compare the two. The snapshot on the left is the AI standard surface with default Bifrost Liquid properties. On the right is an AI standard surface that I customized for this shot. We can see that better transmission and subsurface scattering values not only brightened the fluid, but with global illumination we actually brightened the entire shot. That's how to render a transparent liquid mesh in Arnold.
- Bifröst basics
- Analyzing the node structure
- Emitting from a polygon mesh
- Colliding with a polygon mesh
- Adding velocity, friction, and drag with motion fields
- Optimizing space and time accuracy
- Caching simulations
- Meshing and exporting liquids
- Render-time meshing in Arnold
- Applying channel data to Arnold shaders
- Generating foam from a liquid
- Rendering and shading foam in Arnold