Octane for Houdini

The Universal material is designed to integrate with PBR (Physically Based Rendering) workflows, such as Substance Designer. Where the Diffuse, Specular, Glossy, and Metallic materials isolate parameters to design specific material types, the Universal material can design material characteristics associated with any of the other Material types (Figure 1).

It handles dielectric material (Diffuse and Glossy BRDF) and also metallic materials (Glossy BRDF) with assumed IOR or custom IOR for both dielectric and metallic surfaces. Material IOR in the base layer of the Universal material is also not limited to scalar values, and this can be controlled procedurally with texture-type nodes and OSL shaders connected to IOR texture input pins.

Figure 1: The Universal material parameters

Universal Material Parameters

Transmission Pin - Controls how light passes through a transparent surface. It is closely tied with the Dielectric IOR to control the surface's transparency. It accepts a color, texture, or value as an input. However, a color input provides the most control. To create colored glass, change the color input to something other than black and set the Albedo to black. Transmission is not the same as Opacity. Opacity controls the surface visibility, while Transmission controls the transparency. Use Transmission to create a reflective glass surface, and use Opacity to create a hole in the surface.

Transmission Type - Determines how light refracts.

• Specular - Can be used for glass, liquids, and glossy minerals like gemstones. Use the Dielectric IOR channel to control how light bends through this type of material. This mode works well with the Absorption medium to create realistic liquids, or the Scattering/Random Walk medium to create minerals or cloudy liquids.
• Diffuse - Can be used for semi transparent solids. When combined with a Scattering or Random Walk medium, it is ideal for skin, plastics and other non-glossy semi transparent materials.
• Thin Wall - Can be used for surfaces like soap bubbles or very thin plastics and glass. By itself it’s difficult to see this effect, so it needs either some contribution from the Specular channel or a Coating layer to really stand out.
• Thin Wall (Diffuse) - Can be used for leaves, lampshades, and other very thin objects that still have a strong subsurface scattering effect.

Albedo - The material's base color which controls the overall color of a non-metallic opaque material. It can also color a metallic material which is using the Artistic IOR type.

Metallic - Determines how metallic a surface looks. Lower values make the surface look more dielectric, and higher values make the surface look more metallic. 

Metallic Edge Tint - The color of the edges of the metal material, only used with Artistic and IOR+Color modes.

Specular - Determines the color of glossy reflections for Dielectric materials (when the Metallic parameter is set to 0). Set the Dielectric IOR parameter higher than 1.0 for the Specular parameter to contribute to the surface characteristics. 

BSDF Model- The BSDF (Bidirectional Scattering Distribution Function) determines the amount of light that a material reflects and transmits when light falls on it. Specific geometric properties (the micro-facet distribution) of the surface affects each BSDF, which describes the surface's microscopic shape (i.e. micro-facet normals) and scales the brightness of the BSDF's reflections.

Figure 2: Examples of the BRDF types 

Roughness - Determines how much the Specular and Transmission characteristics spread across the surface. 

Anisotropy - Determines the shape of Specular and Transmission highlights. A value of -1 creates a horizontal shape, and a value of 1 creates a vertical shape. 

Rotation - Controls the Anisotropy shape's rotation. 

Spread - Controls the spread of the tail of the specular BSDF (STD only). 

Dielectric IOR - This IOR controls the specular reflection's or transmission's Fresnel effect. By default, if the Dielectric 1/IOR parameter is empty, then the dielectric specular uses this parameter instead.

Metallic Reflection Mode - This attribute, along with the IOR attributes, provide options for controlling the Index of Refraction across a surface.

• Artistic: This mode will only use the albedo color.
• IOR + Color: This mode uses the albedo color and further adjusts the brightness of the surface using the IOR.
• RBG IOR: This is the most commonly used mode. It uses the 3 IOR values only and ignores the albedo color altogether.

Metallic IOR: Complex-valued Index Of Refraction (n-k*i) which controls the Fresnel effect of the specular reflection for metallic materials. For RGB IOR mode, this serves as the Index Of Refraction for the red light (650nm).

Metallic IOR (Green): For RGB IOR mode, this is the Index Of Refraction for the green light (550nm).

Metallic IOR (Blue): For RGB IOR mode, this is the Index Of Refraction for the blue light (450nm).

Allow Caustics - If enabled, the photon tracing kernel will create caustics for light reflecting or transmitting through the object.

Coating - Provides a second layer of reflection to the surface. 

Coating Roughness - Determines how much the coating characteristic spreads across the surface. 

Coating IOR - Controls the Fresnel effect for the surface's coating characteristics. 

Coating Bump Pin - Much like a regular bump map, this creates fine details on the material’s Coating attribute using a procedural or image texture.

Figure 3: The sphere on the right has an Octane Turbulence texture connected to the Coating Bump attribute 

Coating Normal Pin - This attribute also creates fine details on the surface's coating. A normal map is a special type of image texture that uses red, green, and blue color values to perturb the normals of the surface at render time, giving the appearance of added detail. They can be more accurate than bump maps, but require specific software, such as ZBrush®, Mudbox®, Substance Designer, XnormalTM, or others to generate.

Film Width - Simulates the look of thin film material on a surface, like creating a rainbow color effect that appears on an oil slick's surface. Larger values increase the effect's strength.

Film IOR - Controls the film's IOR by adjusting its visible colors.

Sheen - Provides a second layer of glossiness to the surface.

Sheen Roughness - Determines how much the sheen characteristic spreads across the surface.

Sheen Bump Pin - The sheen layer's bump map. If you don't specify a bump map, the sheen layer uses the default shading normal. Otherwise, it applies the bump-mapped surface to the sheen layer. 

Sheen Normal Pin - The sheen layer's normal map. If you don't specify a normal map, the sheen layer uses the default shading normal. Otherwise, it applies the normal-mapped surface to the sheen layer.

Dispersion Coefficient - This is the B parameter of the Cauchy dispersion model, where normal dispersion is derived through the relationship between the Index Of Refraction and the wavelength of light passing through transparent materials. Increasing the Dispersion value increases the amount of coloration and dispersion in the object’s transmission and in caustics.

Medium Pin - There are three primary types of mediums used with materials: Absorption, Random Walk, and Scattering. Details can be found in the Mediums and Volumes section. 

Opacity - Determines what surface parts are visible in the render. Dark values indicate transparent areas, and light values indicate opaque areas. Values between light and dark indicate semi-transparent areas. Lowering the Opacity value fades the object's overall visibility, or you can use a texture map to vary the surface's opacity. For example, if you want to make a simple polygon plane look like a leaf, you connect a black-and-white image of the leaf's silhouette to the Opacity channel. 

Fake Shadows - Activates the Architectural glass option for all meshes sharing that material. When enabled, specular materials exhibit Architectural glass characteristics with its transparent feature, allowing light to illuminate enclosed spaces or frame an exterior view.

Affect Alpha - Lets refractions affect the Alpha Channel, as long as you enable the Alpha Channel in the Render setting's Kernel parameters.

Bump Pin - Creates fine details on the material’s surface using a Procedural or Image texture. When you connect a grayscale texture to this parameter, light areas of the texture give the appearance of protruding bumps, and dark areas create the appearance of indentation. You can adjust the bump map strength by setting the Power or Gamma values on the Image texture node. These attributes are covered in more detail under the Texture Overview section.

Normal Pin - Creates the look of fine detail on the surface. A normal map is a special type of image texture that uses red, green, and blue color values to perturb the normals of the surface at render time, thus giving the appearance of added detail. They can be more accurate than Bump maps, but require specific software such as ZBrush®, Mudbox®, Substance Designer, XnormalTM, or others to generate.

Displacement Pin - Allows adjustment for the height of points on a surface based on an image value. Displacement differs from Bump or Normal mapping by providing true displacement of an objects surface. Displacement mapping is covered in more detail under the Displacement Overview section.

Smooth - Smooths the transition between surface normals. If this option is disabled, the edges between the polygons of the surface are sharp, giving the surface a faceted look.

Smooth Shadow Terminator - If enabled, self-intersecting shadows are smoothed according to the polygon's curvature.

Round Edges Pin - This creates a shader effect at render time that rounds the sharp edges of objects without modifying and reloading the geometry. Higher values will round the edges more. This is useful to bevel hard edges during render time, like when using low-polygon models. See the Round Edges section for more information.  

Emission Pin - Accepts either a Blackbody emission or a Texture emission node. This parameter makes the material emit light and creates mesh emitters. These node types are covered in more detail under the Mesh Emitter section.

Priority - Used to resolve the ambiguity in overlapping surfaces, the surface priority control allows artists to control the order of preference for surfaces. A higher number suggests a higher priority for the surface material, which means it is preferred over a lower priority surface material if a ray enters a higher priority surface and then intersects a lower priority surface while inside the higher priority surface medium.

Shadow Catcher/Matte Pin - Makes the material a shadow catcher. The material becomes transparent unless there is some direct shadow cast onto the material, which makes it less transparent, depending on the shadow strength.

Custom AOV - Writes a mask to the specified custom AOV.

Custom AOV Channel - Determines whether the custom AOV is written to a specific color channel (R, G, or B) or to all the color channels. 

Layer Pin - Adds a Material Layer above the base material. See the Material Layers section in this manual for more details.

Compatibility Version The Octane version that the behavior of this node should match.