RENDERMAN 22 DOCUMENTATION

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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.

 

 Diffuse Parameters

Diffuse Parameters

The diffuse parameters control the look of basic diffuse reflection. These are often used to define primary color attributes for opaque objects; wood textures, label text, polka dots, or more, you can find them all connected here.

Gain

Gain is the weight applied to the diffuse parameters. You may also drive this with another pattern to show things like fading or wetness (where liquid darkens a surface).



Color

Color is typically where textures or patterns are connected to create color for opaque objects. This is where a wood color texture would go, for example.



Roughness

Diffuse roughness is how you would simulate a powdery surface like dried clay or dust.

 

 

Bump

Normal to use for the diffuse illumination. If this is not set, it will use the global bump normal specified in the Properties section near the bottom of this page.

 

 

Double Sided

If on, illuminate both sides of the surface for this diffuse lobe, that is, this will illuminate the surface whose normal is pointing away from the camera as well.

 Specular Parameters

Specular Parameters

The specular parameters control speculal reflection. This is where you might define how shiny or reflective an object is. Is it plastic, a polished marble table, or  is it a mirror?

Specular Model

Select which specular model to use: Beckmann or Ggx. Ggx may be preferred here for its "tail", or how the highlight has a soft fade from the center reflection of a lightsource.

 

 

Face Color

Specular color at facing angle (0 degree incidence). Note that there is no separate gain control. To control the specular "gain", simply adjust the color value or connect it to a PxrExposure node.

 

 

Edge Color

Specular color at the glancing angle (90 degree incidence). To control the edge specular "gain", simply adjust the color value or connect it to a PxrExposure node.

 

 

Fresnel Exponent

Specular fresnel curve exponent. Lower numbers reduces the effect of Face Color while increasing the effect of Edge Color. Higher numbers reverse this. If your face and edge colors are the same, then there is no visible effect.

 

 

Roughness

Specular roughness. A greater value produces rougher or "blurry" specular reflection. At 1.0 it resembles a diffuse surface and at 0.0 it's a perfectly clear reflection. Most objects will be realistic somewhere in between these values. Texturing this value may give you interesting effects like smudges, greasy fingerprints, and worn surfaces.

 

 

Anisotropy

Controls the shape of the specular highlights and reflections. 0 means isotropy which produces the regular circular specular highlight. Values from -1.0 to 1.0 produce the range of ellipses (stretching) from wide to tall.

By default, the direction of anisotropy is controlled by the model texture parameters. If the Shading Tangent is specified, it is used instead.

 

 

Shading Tangent

Controls the anisotropy direction. Only valid when it is connected to a pattern. This is useful for making brushed metals.

 

 

Bump

Normal to use for the specular illumination. If this is not set, it will use the global bump normal specified in the Properties near the bottom of this page.

 

 

Double Sided

If on, illuminate on both sides of the surface for this specular lobe, that is, this will illuminate the surface whose normal is pointing away from the camera as well.

 

 

Rough Specular

Similar to Specular parameters above except it has a larger default roughness which is 0.6.

 

 

 Clear Coat Parameters

Clear Coat

Clear coats are great for making a top glazed layer found in coated objects or paints like car paint.

Specular Model

Select which specular model to use: Beckmann or Ggx. Again, Ggx might be preferred for its "tail" or fade from the center highlight of reflected light sources.

 

 

Face Color

Specular color at facing angle (0 degree incidence). Note that there is no separate gain control. To control the specular "gain", simply adjust the color value or connect it to a PxrExposure node.

 

 

Edge Color

Specular color at the glancing angle (90 degree incidence). To control the edge specular "gain", simply adjust the color value or connect it to a PxrExposure node.

 

 

Fresnel Exponent

Specular fresnel curve exponent. Lower numbers reduces the effect of Face Color while increasing the effect of Edge Color. Higher numbers reverse this. If your face and edge colors are the same, then there is no visible effect.

 

 

Roughness

Specular roughness. A greater value produces rougher or "blurry" specular reflection. At 1.0 it resembles a diffuse surface and at 0.0 it's a perfectly clear reflection. Most objects will be realistic somewhere in between these values. Texturing this value may give you interesting effects like smudges, greasy fingerprints, and worn surfaces.

 

 

Anisotropy

Controls the shape of the specular highlights and reflections. 0 means isotropy which produces the regular circular specular highlight. Values from -1.0 to 1.0 produce the range of ellipses (stretching) from wide to tall.

By default, the direction of anisotropy is controlled by the model texture parameters. If the Shading Tangent is specified, it is used instead.

 

 

Shading Tangent

Controls the anisotropy direction. Only valid when it is connected to a pattern. This is useful for making brushed metals.

 

 

Bump

Normal to use for the clear coat illumination. If this is not set, it will use the global bump normal specified in the Properties near the bottom of the page. Setting this separately can produce a "glazed" effect where you have a bumpy clearcoat above a smooth surface.

 

 

Double Sided

If on, illuminate on both sides of the surface for this clear coat lobe, that is, this will illuminate the surface whose normal is pointing away from the camera as well.

 

 

 Iridescence Parameters

Iridescence

Iridescence is a view-dependent scattering of light that causes a color shift. This is the same effect responsible for the color swirl on a soap bubble, peacock feathers, or a shiny insect. "Holographic" or color shifting paint uses this effect as well.

Iridescence Mode

Select which iridescence mode to use: Artistic or Physical.

In Artistic mode, we just set 2 colors. Depending on the iridescence scale factor, we will see N number of "rainbows".

 

 

In Physical mode, we pass the thickness of your thin film in nanometer. The iridescence effect happens when the physical thickness is close to the visible spectrum. You can start around 800nm and increase the value to see the effect.

 

 

Face Gain

Iridescence gain at facing angle (0 degree incidence).

 

 

Edge Gain

Iridescence gain at the glancing angle (90 degree incidence).

 

 

Primary Color

This is for Artistic mode only.

Iridescence primary color on the hue wheel to start from.

 

 

Secondary Color

This is for Artistic mode only.

Iridescence secondary color on the hue wheel to end at.

 

 

Falloff Speed

This is for Artistic mode only.

Falloff speed from Primary Color to Secondary Color. Larger numbers falloff more slowly.

 

 

Falloff Scale

This is for Artistic mode only.

This sets how many times the iridescence "rainbows" color repeat.

 

 

Flip Hue Direction

This is for Artistic mode only.

Flip the hue wheel direction between primary and secondary colors. By default, the hue wheel direction is counter clockwise.

 

 

Thin Film Thickness

This is for Physical mode only.

Thin film thickness in nanometers.

 

 

Roughness

Iridescence roughness

 

 

Double Sided

If on, illuminate on both sides of the surface for this iridescence lobe. This is useful for thin opened surface such as feather and leaves that are modeled without thickness.

 

 

Fuzz Parameters

This parameter introduces a bit of retroreflection and helps simulate fabrics, fuzz, and fine powder.

Gain

Fuzz weight. Higher numbers increase this effect.

 

 

Color

Fuzz color. This simulates a soft velvety-like effect. This is applied "on top" of the previous Specular lobes and may resemble dirt or fine dust.

 

 

Cone Angle

Fuzz roughness (corresponding to Marschner R cone angle). Higher numbers increase the effect at facing angles.

 

 

Bump

Normal to use for the fuzz illumination. If this is not set, it will use the global bump normal specified in the Properties near the bottom of this page.

 

 

Double Sided

If on, illuminate on both sides of the surface for this fuzz lobe, that is, this will illuminate the surface whose normal is pointing away from the camera as well.

 

 

 Subsurface Scattering Parameters

Subsurface Scattering Parameters

Subsurface Model

Select a subsurface scattering model: Jensen Dipole, DEon Better Dipole, Burley Normalized - This is the preferred method, and Multiple Mean Free Paths

Burley Normalized produces the most accurate effect while preserving details.

Jenson and DEon Dipoles are great for very translucent objects like gummies.

Multiple Mean Free Paths is great for texturing to produce color bleed easily. While not necessarily physically correct, its intuitive scattering of textured colors works well for art direction.

 

 

Gain

Subsurface scattering weight. Higher numbers increase the visibility of the subsurface scattering.

 

 

Color

Subsurface scattering color.

 

 

Mean Free Path Distance

Subsurface scattering mean free path scalar distance. This specifies how far the light travels inside an object and as a consequence how smooth the subsurface scattering is. This gets multiplied by the unit length set in the Properties section. Higher amounts make the object appear less opaque and more translucent.

 

 

Mean Free Path Color

How far the light travels in the R, G, and B spectra. This is scaled by Mean Free Path Distance. Different colors may spread more or less and provide interesting effects like the red color bleeding into shadow edges on skin.

 

 

Post Tint

Tint that is applied at the end of the subsurface computation. If we want to apply the tint before the subsurface computation, set Irradiance Tint in the Properties section.

 

 

Short Gain

Short subsurface gain or weight. This is only valid for Multiple Mean Free Paths subsurface model.

 

Short Color

Short subsurface color. This is only valid for Multiple Mean Free Paths subsurface model.

 

 

Short MFP Distance

Short subsurface mean free path scalar distance.

 

 

Long Gain

Long subsurface gain or weight. This is only valid for Multiple Mean Free Paths subsurface model.

 

 

Long Color

Long subsurface color. This is only valid for Multiple Mean Free Paths subsurface model.

 

 

Long MFP Distance

Short subsurface mean free path scalar distance.

 

 

Diffuse Computation Switch

Switch the subsurface computation to a diffuse computation if the dmfp is smaller than the ray footprint. This is an optimization to ignore computing scattering, especially on far away objects.

 

 

Double Sided

If on, illuminate on both sides of the surface for this subsurface lobe, that is, this will illuminate the surface whose normal is pointing away from the camera as well.

 

 

Trace Control:

Consider Backside

Whether subsurface respects surfaces on the other side. This is for the hit side, not the illuminating side (which is subsurfaceDoubleSided):

  • "Off" - It will ignore surfaces on the other side completely. This is useful to make objects appear thicker than they are.
  • "On" - Normal mode, where the diffusion happens between the front and the first surface behind it.

 

 

Continuation Ray Mode

Control continuation ray mode:

"Off" - Simply trace out of the object (default).

"Last Hit" - Ignore internal geometry and jump to the last surface.

"All Hits" - Scatter (collect light) on all hits as the ray leaves the object. This can bring additional brightness, at the cost of additional noise.

 

 

Max Continuation Hits

Maximum number of hits to test in all hits mode. This is only valid when Continuation Ray Mode equals All Hits

 

 

Follow Topology

Controls how strongly normals are considered in the subsurface computation. This may affect visible details created through bump mapping as well.

 

 

Trace Subset

Specify trace subset for inclusion/exclusion when struck by a ray indirectly.

 

 

 Single Scatter Parameters

Single Scattering Parameters

Single scatter is a simple and inexpensive effect for scattering effects.

 

 

Gain

Single scatter gain or weight.

 

 

Color

Single scatter color.

 

 

Mean Free Path

Single scattering mean free path scalar distance. This specifies how far the light travels inside an object and as a consequence how smooth the single scattering is. This gets multiplied by the unit length set in the Properties section. Larger values are more translucent.

 

 

Mean Free Path Color

How far the light travels in the R, G,  and B spectra. This is scaled by Mean Free Path Distance.

 

 

Directionality

Single scatter directionality:

1: forward scatter which is more light on the backside.

-1: backward scatter which is more light on the front side.

0:isotropic (no effect).

 

 

Refractive Index

Single scatter index of refraction.

 

 

Blur

Blur strength for single scatter.

 

 

Backside Direct Illum Gain

Gain for direct illumination from the other side.

 

 

Direction Tint

Tinting color for the Backside Direct Illum Gain.

 

 

Double Sided

If on, illuminate on both sides of the surface for this single scatter lobe, that is, this will illuminate the surface whose normal is pointing away from the camera as well.

 

 

Trace Control Parameters:

Consider Backside

Whether subsurface respects surfaces on the other side. This is for the hit side, not the illuminating side (which is singlescatterDoubleSided):

  • "Off" - It will ignore surfaces on the other side completely. This is useful to make objects apear thicker than they are.
  • "On" - Normal mode, where the diffusion happens between the front and the first surface behind it.

 

Continuation Ray Mode

Control continuation ray mode:

"Off" - Simply trace out of the object (default).

"Last Hit" - Ignore internal geometry and jump to the last surface.

"All Hits" - Scatter (collect light) on all hits as the ray leaves the object. This can bring additional brightness, at the cost of additional noise.

 

 

Max Continuation Hits

Maximum number of hits to test in all hits mode. This is only valid when Continuation Ray Mode equals All Hits

 

 

Direct Gain Mode

Control continuation ray mode:

"First Hit" - Simply trace to the next surface (this is tied to considerBackside).

"Last Hit" - Ignore internal geometry and jump to the last surface.

"All Hits" - Scatter (collect light) on all hits as the ray leaves the object. This can bring additional brightness, at the cost of additional noise.

 

 

Trace Subset

Specify trace subset for inclusion/exclusion when struck by a ray indirectly.

 

 

 Glow Parameters

Glow Parameters

Glow can make an object appear to emit light. This is useful when you need a textured effect like lit panels, circuitry, or other complex effects with local influence in lighting.

 

 

Gain

Glow gain or weight.

 

 

Color

Controls the incandescence color, or glow, of the material.

 

 

 

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.

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