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Dielectric#

The dielectric material is designed to simulate refractive materials such as glass or water. It supports both refractive and reflective caustics as well as multiple scattering and transmission scattering.

Glass render using the Dielectric material

Glass render using the Dielectric material

Reflection/Refraction#

The reflection and refraction of the material are respectively controlled by Reflection Color and Refraction Color and the Index of Refraction (IOR) attributes. The material supports Roughness, Anisotropy and multiple microfacet models that can be selected using the Brdf attribute.

BRDF Description
GGX GGX distribution results are very close to empirical data.
Ward Ward distribution is very close to Beckmann's but behave quite differently with anisotropy
Beckmann Beckmann distribution tends to provide sharper reflections when compared to GGX

Roughness to 0%

Roughness to 45% GGX

Exit Color#

The Reflection/Refraction Exit Color attributes define the color returned by the path tracer when the path has reached the maximum reflection/refraction depth set in the path tracer. This is useful is some complex rendering scenarios such as when rendering a crystal like materials.

Anisotropy#

Anisotropy control how much the specular highlight is stretched along a direction defined by Anisotropy Space.

  • When set to Tangent UV the material uses a frame defined by the UV mapping of the texture connected to the Anisotropy Direction, Anisotropy Rotation, Anisotropy, Roughness or Refraction Color attributes.
  • When set to Tangent Parametric the material uses the surface parametric frame whereas in Object it uses the frame defined by the object. Anisotropy Direction defines the direction of the anisotropy on the local surface frame and Anisotropy Rotation defines the rotation of the anisotropy along the direction.

Transmittance#

Transmittance simulates the density of the dielectric medium filtering the color of ray the further it travels through the material.

Transmittance Color defines the reflected color of the medium while Transmittance Density controls the density of the medium which directly translates into the scale factor of the ray attenuation.

The higher the value, the more the color of the ray shifts towards the color defined by Transmittance Color.

No Transmittance

Green Transmittance

Transmission Scattering#

Transmission Scattering simulates the scattering of light inside the medium which can be used to simulate murky water for example.

When enabling Transmission Scattering, the path tracer samples the inner medium of the geometry as a homogeneous volume. While the renders are very convincing they can also be very expensive to render especially when enabling caustics and many bounces.

The maximum number of bounces of the transmission scattering is controlled by Volume Depth attribute.

Effect of transmission scattering on an emissive geometry placed inside a dielectric cube

Effect of transmission scattering on an emissive geometry placed inside a dielectric cube

Shadows and Caustics#

By default, the material renders fake caustics so that shadows are not entirely black. While this approximation can be acceptable in some cases, it is still possible to render proper transmissive caustics by setting Refractive Caustics to Glossy only, Specular only or Full.

However, when enabling transmissive caustics you should change Shadow Casting Mode to Physical. This way the render is physically correct since it doesn't receive too much illumination (pseudo caustics + caustics) from lights.

Pseudo Caustics

Shadow Casting Mode to Physical and enabling Full caustics on Reflection and Refraction

Single Sided vs Double Sided#

By default, the material renders the geometry as filled solid filled. If you render an implicit sphere with a glass dielectric is rendered as a ball fully made of glass.

Setting the Sidedness to Double changes the behavior so that it is rendered as a thin geometry empty on the inside.

Sidedness set to Single default

Sidedness set to Double