Contents
"Finding Dory"
Rendering surfaces in RenderMan relies on a 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 to get you started.
- Flexible controls are not required to result in something 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. 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 effect 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.
Parameters begin below.
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 labels.
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). Below are examples at 0.0, 0.5, and 1.0 gain for a 50% grey material.
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
Bump mapping is a great way to fake the appearance of physical detail using shading instead. 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 (2-dimensional objects) as well.
Specular and Rough Specular Parameters
The specular parameters control specular 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? The Rough Specular lobe below this has identical settings and effects.
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. Left is Beckmann and Right is GGX with roughness 0.25.
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. Below are different choices including textured at roughness 0.25.
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. Below are different choices including textured at roughness 0.25. The Fresnel Exponent is also reduced here to make it more obvious.
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. Below we use a red Face Color and green Edge Color and increase the Fresnel Exponent from 0.1 to 1.5 and finally 5.0 with a small roughness.
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. Below are examples from 0.0 to 0.5 and finally 1.0 (diffuse).
Anisotropy
Controls the shape of the specular highlights and reflections. 0 means isotropic 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. Below are examples of -1.0, 0.0, and 1.0.
Shading Tangent
Controls the anisotropy direction. Only valid when it is connected to a pattern. This is useful for making brushed metals. Below are three examples using textures and an Anisotropy of -10
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
Identical Specular parameters except it has a larger default roughness which is 0.6. This layer is intended for use with higher roughness settings than the Specular lobe above. Below from left to right: Rough Specular, Specular, both lobes combined.
Clear Coat
Clear coats are great for making a top glazed layer found in coated objects or paints like car paint, carbon fiber, and more. You can even use a bump exclusive to this layer to make for convincing coating imperfections. While roughness is available, this layer is intended for low amounts of roughness. You will notice in the parameter examples that the base diffuse is 50% grey to illustrate how this works as a coating. If you need a metallic surface, use the above Specular lobes.
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. Below we use a red Face Color and green Edge Color and increase the Fresnel Exponent from 0.1 to 1.5 and finally 5.0 with a small roughness.
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. Below are values 0.0, 0.5, and 1.0
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. You may even "overdrive" the parameter by going further than -1.0 and 1.0.
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
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 beetle. "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". The default of red and blue is appropriate to get a maximum color spread but you can reduce the number of colors rendered by changing these defaults. Unless otherwise specified or demonstrating an Artistic Parameter, the examples use Physical mode.
In Physical mode, we pass the thickness of your thin film in nanometers. 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. This option is great because it reduces parameters to tweak at the cost of flexibility. Unless otherwise specified or demonstrating an Artistic Parameter, the examples use Physical mode. Below are Artistic (left) and Physical (right) modes.
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. From here the color shifts through the other available hues between the Primary and Secondary Color. The closer on the color wheel your choices, the fewer colors will be rendered. Below are three examples beginning at Red, then Yellow, and finally Green. The color bar shows what colors are available between these choices.
Secondary Color
This is for Artistic mode only.
Iridescence secondary color on the hue wheel to end. As demonstrated above you can use this to limit the colors rendered. Below are three examples where the Secondary Color goes from Violet to Blue and finally to Green. The hue bar shows this change on a ramp.
Falloff Speed
This is for Artistic mode only.
Falloff speed from Primary Color to Secondary Color. Larger numbers falloff more slowly. Below uses the defaults for Artistic Mode but we change the Falloff Speed from 0.1 to 0.5 to 1.0
Falloff Scale
This is for Artistic mode only.
This sets how many times the iridescence "rainbows" color repeat. Below we go from 0.5 to 1.0 and finally 3.0. Notice that higher values begin to repeat the rainbow effect. This is useful for simulating oil patterns such as oil on water or soap bubbles.
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. Left is off, right is on.
Thin Film Thickness
This is for Physical mode only.
Thin film thickness in nanometers. We begin at 400 then 800 and finally 1600 nanometers from left to right. Notice that at 1600 we begin to see a repetition in the rainbow effect. This is similar to the effect of using the Falloff Scale in Artistic Mode.
Roughness
Iridescence roughness, this is like other roughness parameters where you can go from a mirror-like reflection at 0.0 to diffuse reflection at 1.0. Below are examples, left to right, of 0.0, 0.5, and 1.0. Softer looks are reminiscent of color changing makeup and similar powders.
Double Sided
If on, illuminate on both sides of the surface for this iridescence lobe. This is useful for thin opened surfaces such as feathers 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. Below the Cone Angle is set to 16.
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. Below the Cone Angle is set to 16.
Cone Angle
Fuzz roughness (corresponding to Marschner R cone angle). Higher numbers increase the effect at facing angles. Below are values 8, 16, and 32.
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 Model
Select a subsurface scattering model: Jensen Dipole, d'Eon Better Dipole, Burley Normalized, and Multiple Mean Free Paths. The parameters are populated based on the model chosen and are valid for that model. If you change which model you use, your connections may be lost to invalid parameters.
Burley Normalized produces the most accurate effect while preserving details.
Jensen and d'Eon 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 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. Small amounts make the surface appear as a simple diffuse and it may be more efficient to turn off the effect (0.0 Gain) if it's not visually important.
Mean Free Path Color
How far the light travels in the Red, Green, and Blue 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. The RGB values correspond to how far the light travels in that color band. For example, and RGB value of 0.8 0.65 0.5 mean Red spreads furthest at 0.8, then Green and finally Blue traveling the least distance in the object scatter result. Below we've taken out the center sphere and replaced it with a bright disk light at the back of the outer sphere.
Post Tint
Tint that is applied at the end of the subsurface computation. Below on the left is a normal render and on the right a very light blue tint is added. 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.
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.
Short MFP Distance
Short subsurface mean free path scalar distance.
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 (not visible given the settings and distance). This is an optimization to ignore computing scattering, especially on far away objects or objects where the scattering scale is so low a diffuse computation is visually similar and much faster.This may be easier than manually setting the Gain to 0.0.
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.