Enables diffuse reflection.

The proportion of incoming light reflected back as the diffuse component, from 0 (no diffuse reflection) to 1 (all incoming light is reflected). Non-attenuated lights such as point lights and spot lights may produce brighter pixel values than this value.

(Old shaders such as the VEX Plastic shader implicitly have a reflectivity of 0.5 when the shader’s diffuse coefficient is set to 1.)

When Fresnel Blending is on, controls the minimum amount of reflection that will not be blended with the Fresnel factor. Diffuse components are blended with the transmissive Fresnel component.

Fresnel blending of the diffuse component only makes sense when one or both specular reflection layers are on. If there is no specular reflection, you should turn off Fresnel Blending.

The color reflected by the object (technically, the reflectivity of red, green, and blue color components).

A floating point value used to control the size or spread of the diffuse component. Higher values make the surface look less glossy with flatter color.

Specifies a label for the BSDF component. This can be used to export contributions from this component to a separate image plane.

Simulate subsurface scattering of light through the object.

The overall proportion of light that is scattered, from 0 (no scattering) to 1 (all light is scattered). Higher subsurface albedo values will produce more multiple scattering and a greater scattering distance.

The dominant color in lit areas of the surface.

The minimum scattering intensity.

How quickly the light intensity decreases as it scatters. Higher values make the lighting level decrease faster. Available when Parameter mode is Artist.

The color tint that light takes on as it’s scattered under the surface. In practice, this controls the “far side” color of subsurface scattering.

Controls the nature of the scattering. Positive values give forward scattering, 0 gives isotropic scattering, and negative values give backscattering. Range is -1 (full backscattering) to 1 (full forward scattering).

The value depends on the type of material you are trying to model. For example, skin is highly forward scattering, while marble is backscattering.

Enables independent scattering of the red, green, and blue color components. When enabled, an independent scattering and absorption coefficient will be used for each color component, leading to more accurate renders - though the results can sometimes show colors that are complementary to the attenuation color. For example, with a blue attenuation color, shorter scattering distances will render with a yellow tint. To partially eliminate this unpredictable effect, disable this toggle.

Enable/disable contribution from light that scatters exactly once in the surface. Certain types of surfaces (such as skin) gain little contribution from single scattering and so disabling this option will reduce computation time with little impact on accuracy.

A scaling factor for the contribution of single scattering to the surface color, from 0 (no contribution) to 1 (full contribution).

The number of samples for single scattering. Increase this option to decrease noise at the expense of slower shading.

Enable contribution from light that scatters more than once in the surface. For low albedo materials (low Subsurface Albedo), multiple scattering contributes little to the image and can be disabled to reduce computation time.

Controls the way in which multiple scattering is computed. Normally you should use the Local And Global mode if you are planning to use a point cloud, and Ray Tracing to compute multiple scattering without a point cloud. Using a point cloud can produce smoother and faster results, but it requires precomputation of a point cloud and computation of irradiance for each point in the cloud (once per render).

Controls how the shader generates a point cloud. The simplest option is to select Generate At Render Time. This will create a new point cloud for every render. To reduce computation time, you can first use Write To File mode and then re-use the point cloud using Read From File mode on subsequent renders. This is also the recommended approach when rendering animations because the shader will smoothly interpolate the point cloud across frames. The exception to this is when the model’s topology changes (two joined polygons are separated, for example). In this case, a new point cloud must be generated. Note that in Write To File mode, the file will be overwritten if it already exists. Cancelling a render before it completes in Write To File mode may result in an unusable point cloud file.

See managing point clouds for more information.

Controls the file the point cloud is written to/read from when Point Cloud Mode is Write To File or Read From File. The point cloud is based on surface UVs, so it is not necessary to write a new point cloud file for each frame unless the topology of the model is changes.

A scaling factor for the contribution of multiple scattering to the surface color, from 0 (no contribution) to 1 (full contribution).

Controls the number of samples in the point cloud. Low values give fast renders but a sharper, less accurate look. High values give slower renders but a blurrier, more accurate look.

Enables this reflection layer.

Light sources (including environment lights) will be reflected. Light source reflections are commonly known as “Specular Highlights”.

The mathematical model used to simulate glossy reflections. For each viewing angle and surface normal, the model defines from which directions and at what intensity light is reflected. This is what shapes specular highlights and reflections in general.

The overall glossiness, and with it the size of highlights, is controlled by Roughness. The available models simulate the effects caused by Roughness with varying degrees of physical accuracy, with GGX currently being the most accurate.

The chosen model has no effect when Roughness is 0, since this causes light to be reflected from a single direction at full intensity, making the model irrelevant.

See Roughness for more information.

The figure below shows the result produced by various specular models across a range of roughness values.

Note how rough surfaces look more natural with the GGX model because the interaction of light with the rough surface is modeled more accurately.

The proportion of light that is reflected by this specular layer, from 0 (no light reflected) to 1 (all light is reflected).

When Fresnel Blending is enabled, controls the proportion of specular reflection that will not be blended with the Fresnel factor. Increasing this parameter will cause a minimum amount of reflection to appear even for rays perpendicular to the surface.

The tint of the specular highlight (technically the reflectivity for the red, blue, and green color components). For example, setting the specular color to 1, 0, 0 will reflect only red light, giving red highlights.

Controls how metallic reflections appear. This uses a different method of calculating reflection intensity that is physically correct for conductive materials.

Controls the tint color used for the metallic reflection model. This controls the color around the edges of objects (where the surface is seen at a grazing angle). Metals typically have a slightly different tint in these regions.

This is a measure of how bumpy a surface is at the microscopic level. The most obvious effect is that reflections become glossier as Roughness increases. At a value of 0, the surface is perfectly smooth and produces perfect mirror reflections. A value of 1 simulates a very rough surface, which results in very blurry reflections, similar to diffuse reflection.

In more accurate Specular Models like GGX, reflections on rough surfaces are also darkened at grazing angles. This is due to Masking-Shadowing effects, where parts of the surface are hidden from view and/or not reached by light due to microscopic grooves and spikes in the surface. Note that this is simulated using a simplified mathematical model, rather than using actual additional geometry.

The visual change when transitioning from 0 to 1 is close to linear.

Causes reflections to be stretched in the direction defined by Anisotropy Direction.

This simulates microscopic bumps with a directional bias, causing light to be scattered more in the defined direction. This is typical of brushed metals.

The effect of this parameter increases with Roughness. It has no effect at all when Roughness is 0.0.

Controls the direction of Anisotropy relative to the UV coordinates of the surface. At 0.0, reflections are stretched in the U direction. At 0.5, the direction is rotated by 90 degrees to the V direction. 1.0 equals 180 degrees. Since the effect is symmetrical this produces the same result as 0.0.

The direction of rotation also depends on the UV layout. When the UVs are layed out such that textures appear on the surface without mirroring, higher values rotate counter-clockwise.

The effect of this parameter diminishes with decreasing Roughness and Anisotropy.

This reflection layer will reflect other objects in the scene, using raytracing.

Enables separate roughness, intensity, and color parameters for object reflections, independent of the parameters for specular reflections. This lets you create artistic (physically unrealistic) differences between the object reflections and light reflections.

The intensity to use for object reflections, when Separate object reflection parameters is on. This overrides Specular Intensity.

A tint color for object reflections, when Separate object reflection parameters is on. This overrides Specular Color.

The roughness used for object reflections when Separate Object Reflection Parameters is enabled.

Specifies a label for the BSDF component. This can be used to export contributions from this component to a separate image plane.

Turns on simulation of light refracting through the object.

Light sources (including environment lights) will appear in refractions.

The mathematical model used to simulate glossy refractions. For each viewing angle and surface normal, the model defines from which directions and at what intensity light is refracted. This is what shapes highlights and refractions in general.

The overall glossiness, and with it the size of highlights, is controlled by Refraction Roughness.

The chosen model has no effect when Refraction Roughness is 0, since this causes light to be refracted from a single direction at full intensity, making the model irrelevant.

The proportion of light refracted by the surface, from 0 (no light refracted) to 1 (all incoming light is refracted).

When Fresnel Blending is on, controls the proportion of refraction that will not be blended with the Fresnel factor. Increasing this parameter will cause a minimum amount of refraction to appear even for rays that graze the surface (and so would normally not refract).

A tint for the refracted light (technically, the refraction amount for different color components). For example, setting the refraction color to 1, 0, 0 will cause the surface to refract only red light.

Roughness is a measure of how bumpy a surface is at the microscopic level. The most obvious effect is that refractions become glossier as roughness increases.

At a value of 0, the surface is perfectly smooth and produces perfect refractions like glass. A value of 1 simulates a very rough surface, which results in very blurry refractions, like milky glass.

The visual change when transitioning from 0 to 1 should be close to linear.

The direction and amount of anisotropy in the refraction. Values less than 0 will sharpen the refraction in the U direction while values larger than 0 will sharpen the refraction in the V direction. When the Refraction Anisotropy is -1 or 1, refractions will have a width of 0 in the other direction.

The angle to rotate anisotropic refrations. A value of 0 will align it directly with the parametric directions while other angles rotate clockwise.

Show refractions of objects. You should normally leave this option on (otherwise no refractions will appear) unless you are simulating a single sheet of reflective material, and you still want light to filter through the object.

Tint the refractions based on the distance the light traveled through through the object, with rays that travel further through the object being more opaque.

The density of the material, for calculating attenuation (see above). Larger density values make the material appear more opaque. Setting the density to 0 is the same as turning off attenuation.

The color to tint light passing through the object. Technically, this is the inverse of the color that is absorbed (the opacity).

Treat the surface of the shaded object as a thin refractive film rather than the boundary between the outside of the object and a solid interior. Turn this on to simulate hollow and/or thin refractive objects such as bubbles or windows. The node still uses the refractive index to calculate the proportion of reflection and refraction for fresnel blending, but the transmitted ray will not change direction.

Specifies a label for the BSDF component. This can be used to export contributions from this component to a separate image plane.

Add a constant amount of diffuse light emitted from the surface. For example, with emission on, the object would be visible in the render even if none of the light objects were shining on it. This may be useful in some circumstances, but normally you should simply use an Area Light to add light to the scene more efficiently and controllably, especially if you need to add a lot of light.

The amount of emission.

The color of the emitted light.

The light emitted by this object will brighten the surfaces of other objects. When this option is off, the emitted light will be visible in the camera, but will not fall on other objects in the scene.

Scales the value of the Opacity parameter. This is useful as a single number to manipulate rather than having to change all three components of the Opacity parameter together.

The opacity for each color component.

Transmissive objects produce semi-transparent shadows that attempt to approximate the amount of light that would be transmitted if real caustics were rendered. If you're rendering real caustics using an Indirect Light, turn this parameter off.

The minimum shadow intensity to use for fake caustics. Increase this to darken the lightest part of the shadow.

The maximum shadow intensity to use for fake caustics. Decrease this to lighten the darkest part of the shadow.

Blend between different opacities for parts of the surface that are perpendicular (head-on) to the camera and parts that are parallel (edge-on).

The opacity to use for rays that are parallel to the surface normal, when Enable opacity falloff is on.

The opacity to use for rays that are perpendicular to the surface normal (rays that graze the surface), when Enable opacity falloff is on.

Controls the blending point between parallel and perpendicular opacity. Values larger than 1 give more parallel opacity, values smaller than 1 give more perpendicular opacity.

The interior index of refraction for use in physical Fresnel computations. Water has an index of refraction around 1.33.

The exterior index of refraction for use in physical Fresnel computations. Air has an index of refraction near 1.

Ensures that the surface reflects no more light than it receives. This is important in physically based rendering and raytracing to ensure the illumination in the scene does not increase as the number of raytracing bounces increases. For example, a surface that reflects twice as much light as it receives (by turning off Conserve Energy and setting the Specular Intensity to 2) would produce a unnaturally bright render as you increase the Reflect Limit.

This setting conserves energy by scaling the BSDF by the inverse of its reflectivity when the node detects the reflectivity is greather than 1. This reduces all components of the Classic Shader Core by the same factor, linearly darkening of the surface.

You can calculate the total reflectivity of a surface (assuming Fresnel Blending is off) by summing the Diffuse Intensity, Specular Intensity (for each layer) and Refraction Intensity. For predictable results, you should try to conserve energy manually by limiting the intensity or reflectivity parameters.

Turns on Fresnel blending, where the reflection and/or refraction amount varies based on the viewing angle to the surface. This allows you to simulate materials such as glass and water. You can control the proportion of Fresnel blending for each component through the “minimum” parameters on the different tabs (for example, Diffuse Minimum on the Diffuse tab).

Diffuse and Refract components use the transmissive component for Fresnel blending, while Reflect components use the reflective component.

How the Fresnel blending factor is calculated, either from parameters or the Fresnel input.

Automatically flip normals if necessary so planal surfaces are diffuse shaded the same way regardless of normal direction. This setting does not apply to refractions and Fresnel reflections since they rely on the normal direction to define inside and outside for Fresnel blending.

Controls how this node calculates the direction of anisotropic reflections/highlights.

For reflections and refractions in non-PBR renders, treat rays that travel farther than this distance (in Houdini world space units) without intersecting any geometry as missed rays.