Contents
Rendering surfaces in RenderMan relies on a single layerable material called PxrSurface.
This is the same material model used in Pixar Animation Studios' feature animation. As such there are some important benefits to this material:
- A single material handles all your looks like:
- Wood
- Skin
- Plastic
- Glass
- Car Paint
- and many many more!
- Physically based presets provided.
- Flexible controls are not required to be physically plausible.
- Artists can selectively "break" energy conservation.
- Art direction becomes natural without workarounds.
- Layering provides limitless possibilities.
As an artist, being able to choose a single material for all your shading eliminates guesswork and allows RenderMan to optimize as needed. Below we discuss all the different settings and their relevance to making certain materials. Pay special attention to notes about performance considerations as well as hints on what combinations will be useful for particular effects.
Below you will find each section or lobe of the material has been separated into its own section to help users define the area they wish to learn about. However, as different lobes are activated and tweaked, the material will change looks. It's by combining these lobe settings that you can make just about any material you imagine.
Input Material
Connect to a layer pattern that layers the parameters for the Bxdf. This lets users create more complex looks through layered effects. Examples might be dust, scratches, or even bottle labels.
Reflection/Refraction Parameters
Refraction Gain
Refraction gain.
Reflection Gain
Reflection gain.
Refracton Color
Refraction color.
Roughness
Refraction and reflection roughness.
Refractive Index
Index of refraction.
Thin
If on, correctly split energy according to Refractive Index between reflection and refraction, but do not bend the ray in refraction (simulating a double pane of glass with a single pane).
Interior Parameters
Single Scatter Albedo
Single scatter albedo. Connect this to a 3D pattern to control the intensity of the scattering.
Single Directionality
Controls the directionality of the scattering.0 : isotropic1 : forward-1 : backward
Extinction
Extinction color. Connect this to a 3D pattern to control the density of the interior.
Integration Mode
Control volume integration type:Ray MarchingRatio Tracking. Unused, this is currently internal to the PixarAnimation Studios.
Min Extinction Color
Minimum extinction color.
Max Extinction Color
Maximum extinction color.
Step Size
Ray marching step size. Step size is based on the resolution of the 3D pattern that is connected. Inadequate step size will produce artifacts.
Max Steps
Max number of steps.
Properties Parameters
Bump
Normal to use for all illumination unless it is overriden by the individual lobe's bump normal.
Presence
Connect a mask here to apply a cutout pattern to your object. Presence is defined as a binary (0 or 1) function that can take on continuous values to antialias the shape. Useful for creating leaves and other thin, complex shapes.
IMPORTANT NOTE: This value should be either 0 or 1. A value between 0 and 1 will produce unwanted noise !!!
Presence Cached
Specify whether presence is cached or not.
Shadow Mode
Shadow opacity computation mode:
- Shader and shadow color (0)
- Shadow color only (1)
Shadow Color
Specify shadow color.
Specular Energy Compen
Applies fresnel energy compensation to diffuse and subsurface illumination lobes. A value of 1.0 attempts to fully balance those illums by darkening them against the specular and rough specular illumination responses.
Specular and Rough Specular roughness are also taken into account. The effect fades off as specular face or edge color approaches 1.0, so metals can add a diffuse baseline.
Clearcoat Energy Compen
Applies fresnel energy compensation to all lobes other than clearcoat itself. A value of 1.0 attempts to fully balance those illums by darkening them against the clearcoat illumination response.
Clearcoat roughness is also taken into account. The effect fades off as clearcoat face or edge color approaches 1.0, so metals can add a diffuse baseline.
Irradiance Tint
A tint applied to illumination before being scattered by subsurface or single scatter.
Unit Length
Subsurface and single scatter unit length. It is a multiplier on Mean Free Path Distance. Mean Free Path Distance is often measured in millimeters. If the scene is modeled in some other scale, Unit Length should be set accordingly. The default value of 0.1 is appropriate for scenes modeled in centimeters and Mean Free Path Distance measured in millimeters.
Utility Pattern
Note that there is no inputAOV in PxrSurface because we can wire the connection to the utilityPattern instead. It produces the same result as inputAOV. Utililty pattern can be used for other purposes.
It is a dynamic array of utility patterns that get evaluated but their results are not used by this bxdf.
A utility pattern is useful to find out how much this object gets sampled and for collecting statistics so you could theoretically prune and optimize the scene. Once this information is collected, you should disconnect the utility pattern because it is expensive to evaluate. Also, if you need to collect information about shadow rays, you need to set the Shadow Color to greater than 0.0 so the utility pattern is invoked.