Quick Tip: Using RenderMan Lama (Patreon)

One of RenderMan’s best features is its Lama material layering system. Lama was developed at Industrial Light & Magic to enable advanced, modular and modern material construction. I find it preferable to the “old” PxrSurface workflow for several reasons, which we’ll get into below.

But first, one disadvantage: at this point, Lama doesn’t work with RenderMan’s hybrid CPU/GPU mode, XPU. This means that when working with Lama we’re stuck on CPU only. Depending on your system this can be significantly slower than XPU.

With that in mind, let’s dive in!

Lama is a layering system, meaning it allows us to manually build and combine various elements of a material. Most other renderers are also built around the idea of layering, but it is often obscured from the user somewhat through the use of “uber” materials such as PxrSurface or Arnold Standard Surface. These materials combine every commonly-used layer into one node and let us set basic mixing parameters. For example, PxrSurface has a Subsurface Gain parameter that lets us control that layer’s contribution to the final look.

To start building some Lama layers we’ll first attach a Lama Surface node to an object in our scene. (I’m using Blender, but the workflow is identical in all DCCs.)

There are a number of settings here, including if the material is single or double-sided and if things like subsurface should be calculated. We’ll be using subsurface, so that in particular should be enabled. All settings are optional depending on your material, so feel free to enable or disable them as needed.

Attach a Lama Layer. We’ll be using two layers, subsurface and specular (dielectric).

To create our base subsurface layer, attach a Lama SSS node to the Material Base input.

Start up an IPR session and dial in the colors and other settings as desired.

Before we continue, this is a perfect place to point out one reason I prefer Lama over PxrSurface.

PxrSurface’s SSS parameterization is highly technical, particularly the “mean free path distance” terminology. I think most users will find it hard to understand. It’s much more abstract than any other renderer’s subsurface controls.

Lama fixes this by having artist-friendly parameters that will be familiar from other renderers. Color, Radius and Scale are all you need most of the time.

You don’t sacrifice power; all the PxrSurface-style stuff is still available for those who want it. But the initial entry point to the workflow is more accessible and lets you get up and running more quickly.

As we get our SSS dialed in, the total absence of reflections should be pretty obvious! To address this, we’ll add our next layer: Lama Dielectric. A dielectric surface is, basically, glass or plastic. (A Lama Conductor layer would give us metallic reflections.)

Attach our Lama Dielectric to the Material Top input and set Top Mix to 1 (full specular intensity).

We can now work on getting our reflections looking nice.

This brings me to my second reason for preferring Lama for this type of material. The default PxrSurface specular workflow uses unintuitive parameters that, again, are unlike any other renderer. To get “normal” reflections on a glass type material you’d set Primary Specular Face Color to almost, but not quite, black, which results in bright white highlights. Setting this closer to white actually gets you into metal territory which may or may not be desired.

Lama Dielectric to the rescue! Just leave Reflectivity at its default value and set the Reflection Tint and Roughness as desired.

As before, you won’t be sacrificing any power using Lama Dielectric, but quickly getting nice results out of the box is much easier.

Note that for this sample material it makes sense to set the Transmission Tint to pure white. If we view the dielectric material on its own (connect it to the Lama Surface, bypassing the layering setup) we can see that this layer is translucent white glass.

Our final material is not translucent, but when it comes to the layering behavior we don’t want the dielectric layer to affect the appearance of the subsurface. Any Transmission Tint other than white will change the color of the SSS, so it’s best to leave it white.

And that’s all there is to it!

We’ve got an incredibly good looking plastic-type material now and thanks to Lama’s parameterization it was a breeze to set up. You can add lots and lots more layers, controlling the strength of each using noises or image textures, letting you build extremely detailed materials. It’s incredibly powerful and flexible. Give it a try, I think you’ll find it a very satisfying way of working in RenderMan!