Coat

Coat simulates an additional transparent layer on top of a base material, common in automotive paints, polished wood, and plastic coatings. This layer adds a second specular reflection with its own roughness and intensity values, independent of the underlying material properties.

Parameters

Display Name	Name	Type	Default
Weight	coat_weight	float	0.0
Color	coat_color	color	1.0, 1.0, 1.0
Roughness	coat_roughness	float	0.1
IOR Preset	coat_ior_preset	enum	ior_custom
IOR	coat_ior	float	1.5
Anisotropy	coat_anisotropy	float	0.0
Rotation (rad)	coat_anisotropy_rotation	float	0.0
Affect Color	coat_affect_color	float	0.0
Affect Roughness	coat_affect_roughness	float	0.0
Normal	coat_normal	float3	state::normal()

This layer models GGX microfacet dielectric BRDF top coating. Due to Fresnel, this layer is not energy conserving. Thus the energy that is not reflected is transmitted to the underlying layers.

The coating simulates an infinitely thin shell dielectric layer, i.e., glass, enamel, lacquer, over the surface. It can create materials like metallic car paint, carbon fiber, oily skin, and wet asphalt.

Weight

This parameter sets the amount of surface coating. Lowering this value increases light transmission through the object’s volume.

Tip

For a realistic result, this parameter should be set to less than 1.0.

Coat Weight: 0.0

Coat Weight: 0.5

Coat Weight: 1.0

Color

This parameter tints all layers below the coating layer. In the real world, lights scattered by underlying layers are tinted when transmitted through the colored coating.

Coat Color: None

Coat Weight: 0.0

Coat Color: 1.0, 1.0, 1.0

Coat Weight: 1.0

Coat Color: 0.0, 1.0, 0.0

Coat Weight: 1.0

This parameter emulates the effect of absorption within the coating medium.

Without Coat

Base Color: White

Coat Color: Cyan

Base Color: White

Without Coat

Base Color: Yellow

Coat Color: Cyan

Base Color: Yellow

Note

The reflection color is set to white for this layer.

Roughness

This parameter sets the surface microfacet’s irregularities that cause light diffusion. At 0.0 simulates a perfect and smooth reflective surface, while increasing the value causes reflective highlights to diverge or appear blurred.

Tip

Roughness can be used to create effects like torn surfaces or surfaces with fingerprints and smudges.

Coat Roughness: 0.0

Coat Roughness: 0.5

Coat Roughness: 0.75

Coat Roughness: Texture

IOR Preset

This parameter presents a list of known IORs (index of refractions) for various materials, including glass, ice, diamond, skin. One can use custom IOR by setting this parameter to ior_custom and a value for the specular reflection’s IOR parameter.

IOR

This parameter sets IOR (index of refraction), which affects surface Fresnel reflectivity. The IOR defines the ratio between reflection on the surface front, facing the viewer, and the surface edges, facing away the viewer.

At values above 1.0, the reflection appears stronger on the surface edges and weaker on the surface front. At values less than 1.0, the Fresnel is disabled, and the coating appears as a uniform highlight over the surface.

Coat IOR: 1.0

Coat IOR: 1.52

Coat IOR: 5.0

Anisotropy

his parameter sets the specular reflection anisotropy. Reflectance changes based on the surface orientation are called anisotropic. If the reflectance is uniform in all directions and does not change based on the surface’s rotation or orientation, it is isotropic.

At values above 0.0, the surface transmits and reflects incoming light with a directional bias. Thus it appears rougher in a specific direction.

Coat Anisotropy: 0.0

Coat Anisotropy: 0.5

Coat Anisotropy: 1.0

Rotation (radian)

This parameter sets the orientation of the anisotropic effect in radians. At 1.0, the anisotropic effect is rotated by 180 degrees. For brushed surfaces, the anisotropic effect should stretch out in a direction perpendicular to the brushing direction.

Coat Anisotropy Rotation: 0.5

Coat Anisotropy Rotation: 0.65

Coat Anisotropy Rotation: 0.7

Affect Color

This parameter controls the saturation of diffuse reflection and subsurface under the coating layer.

In the real world, refracted rays exhibit internal reflection within the coating medium, which can go back down to the underlying surface to reflect again, thus making the surface more saturated and darker. Affect Color can be used to emulate this effect. At 0.0, this parameter has no effects.

No Coat

Coat Affect Color: 0.0

Coat Affect Color: 1.0

Affect Roughness

This parameter controls the roughness of the specular reflection, and specular transmission under the coating layer.

In the real world, refracted rays exhibit internal reflection within the coating medium, which can go back down to the underlying surface, which may scatter due to the roughness of the undercoating surface. Affect Roughness can be used to emulate this effect. At 0.0, this parameter has no effects.

Base Layer Only

Specular Reflection Weight: 1.0 Specular Reflection Roughness: 0.0

Coat Layer Only

Coat Weight: 1.0 Coat Roughness: 0.5

Base and Coat Layer

Coat Affect Roughness: 0.0

Base and Coat Layer

Coat Affect Roughness: 1.0

Base Layer Only

Coat Layer Only

Base and Coat

Normal

This parameter sets the “normal direction” for the coating layer, which affects the Fresnel blending of the coating layer over the surface. The coat normal can create surface effects like raindrops, imperfections in car paint, or glazing on the food.

Note

The “coat normal” only affects the coating layer and has no effects on the underlying surface normal.

Droplets

Scratches