Corona Physical Material

The new Physical Material is introduced in Corona Renderer 7 for 3ds Max and Cinema 4D. This material has been designed from the ground up and is intended to replace the previously default Corona Material, which in version 7 is called Corona Legacy Material. Some of the benefits of the Physical Material are its ease of use and its ability to achieve realistic results ensuring you can't accidentally create unrealistic "fake" materials that break energy conservation and other laws of physics regardless of the settings you use. The result will always be (and look) realistic.

The Physical Material also includes presets that you can easily select from a dropdown menu. These include materials such as Aluminium, Brass, Chrome, Copper, Diamond, Glass, Gold, Iron, Mirror, Plastic, Plexiglass, Satin, and even Velvet.

Apply preset – Sets the material parameters to the selected preset. Changing the preset does not modify the attached maps.

Metalness – Metals (conductors) are defined mostly by their reflection color:

Metals – Metals (conductors) are defined mostly by their reflection color.
Non-metals – Non-metals (dielectrics) are usually defined mostly by their diffuse color and may be transparent to represent materials like glass or plastic (depending on the refraction amount). When using texture, value 0 represents non-metal and value 1 represents metal. The value in between represents a mixture of metal and non-metal material.

Thin shell (no inside) – Simulates a thin shell with no internal volume. Such material has no refraction, no volume scattering, and no subsurface scattering. Refraction is replaced by opacity and volume absorption by Absorption color, while subsurface scattering is replaced by diffuse reflection and translucency. For example, use this to create windows or leaves with a single plane.

Base Layer

Level – Both the constant color and texmap will be multiplied by this number. Settings 0.5 and using white color is equal to using 50% gray color or using texmap with output level 0.5.

Color – Defines reflection color for metals (conductors) or diffuse color for non-metals (dielectrics).

Roughness – Controls the smoothness of the base layer surface. A value of 0 (black if a map is used) fives a completely smooth surface, which leads to sharp reflections (and possibly refractions) from the base layer. On the other hand, a value of 1 (white if a map is used) gives completely rough surfaces leading to blurred reflections. The smoothness of the surface also influences the diffuse reflections, where the smooth surface gives the perfect Lambert reflection and the rough surface leads to a more flat-like appearance.

IOR – Sets the Index of Refraction (IOR) for a non-metal (dielectric) object, which controls how much a ray is bent when entering the object and the amount of reflection in a physically plausible way. A value of 1 gives non-bending of the ray and non-reflection, while the value of 1.52 is good for a generic glass. Precise values for the IOR of different non-metal (dielectric) materials can be found in various online references and guides.

Bump – The missing coefficient between the texture and constant color. 100% means only the constant color is used, and the value in-between blend the texture with the constant color.

Edge color – Determines metal reflection color for rays hitting the object at the grazing angle.

Anisotropy

Amount – Anisotropy of the glossy reflection highlight. A zero value disables anisotropy (creates a perfectly isotropic highlight). A value of -1 creates a maximally anisotropic highlight on one axis, and a value of 1 creates a maximally anisotropic highlight on the perpendicular axis. The anisotropy reference frame can be defined in the Advanced options tab.

Rotation – Rotates the direction of the anisotropy highlight. Value in degrees.

Translucency

Fraction – A fraction of diffuse reflection that is reflected on the other side of the material using the Thin mode. A value of 1 leads to a full translucency effect and zero diffuse reflection, while the value of 0 disables translucency.

Color – Determines the color of the translucency effect-diffuse reflection on another side of material using Thin mode.

Refraction

Amount – Sets the amount of refraction in the non-metal (dielectric) object. The value of 0 leads to a plastic-like appearance with a diffuse reflection defined by the base color. The value of 1 leads to a glass-like appearance. the values in between result in the mixture of plastic and glass material.

Caustics (slow) – Enables physically correct unbiased caustics. When off, faster, transparent shadows are used.

Thin absorption – Simulates a volumetric absorption in a glass using a Thin mode.

Dispersion – The Abbe number is a measure of the dispersion of the material, with lower values indicating greater dispersion. For most materials, a value between 30 and 60 should be used. Values lower than 10 lead to highly unrealistic dispersion.

Opacity

Level – Both the constant color and texmap will be multiplied by this number. Setting 0.5 and using white color is equal to using 50% gray color or using texmap with output level 0.5.

Color – Allows choosing the opacity color using Corona Color Picker.

Displacement

Min level – Displacement distance applied to areas with black (0.0) texture. Measure in world space units.

Max Level – The strength of the displacement effect. It is the world-space displacement distance applied to areas with white (1.0) texture.

Water level – Displacement cutoff threshold. Any micro triangles with displacement texture value below this level are removed.

Clearcoat Layer

Amount – Sets the strength of the clearcoat layer. A value of 1 leads to a full clearcoat effect, while the value of 0 disables clearcoat.

IOR – Sets the Index of refraction (IOR) of clearcoat layers, which controls the amount of reflection in a physically plausible way.

Roughness – Controls how sharp or blurred the reflection of the clearcoat layer is.

Absorption – Allows choosing the absorption color using Corona Color Picker.

Bump – The mixing coefficient between the texture and constant color.

Sheen Layer

Amount – Sets the strength of the sheen layer. A value of 1 leads to a full sheen effect, while the value of 0 disables sheen.

Color – Sets the color of the front reflection of the sheen layer.

Roughness – Sets the roughness of the sheen surface. Low roughness keeps the specular highlight at the grazing angles, and as it increases the sheen reflection dominates.

Volumetric Scattering

Absorption color – Absorption is controlled by setting the color that an originally white ray has after traveling the specified distance in the medium. A lower distance value makes the effect stronger. Distance 0 is a special value that disables the effect completely.

Distance – Absorption is controlled by setting the color that an originally white ray has after traveling the specified distance in the medium. Lower distance values make the effect stronger. Distance 0 is a special value that disables the effect completely.

Scattering color – Strength and color tint of the volumetric scattering inside the material. Setting a non-black value enables volumetric scattering/SSS effects for this material, it gets multiplied by this value.

Directionality – Directionality of scattering. 0 produces isotropic (diffuse) scattering, positive values produce forward scattering and negative values produce backward scattering. A default value of 0 is suitable for most media, with the exception of clouds where a higher positive number produces the effect of a silver lining. Values close to 1 or -1 increase the amount of image noise.

Single bounce only – When enabled, only a single bounce (direct lighting) is scattered in the medium. This results in a biased (darker) but faster rendering. Useful e.g. for rendering god rays.

Subsurface Scattering

Amount – Controls how much the material color is defined by subsurface scattering as opposed to diffuse reflection. A value of 0 results in no subsurface scattering, while a value of 1 results in full subsurface scattering and no diffuse component.

Radius – Defines the subsurface scattering radius, i.e. how far the color scatters from a place that was hit by a light beam.

Scatter color – Defines the scatter color of subsurface scattering, i.e. the color that can be observed in the shadowed parts of the material.

Self-illumination

Multiplier – Both the constant color and texmap will be multiplied by this number. Setting 0.5 and using white color is equal to using 50% gray color or using texmap with output level 0.5.

Color – Allows choosing a self-illumination color using Corona Color Picker.

Anisotropy Orientation

Local axis – Specifies how to compute the base direction of the anisotropic highlight (before any user-specified rotation offset/map is applied). Local axis - the highlight direction rotates around the local object Z axis. It will stick with the object when it is rotated/moved.

UVW – The highlight direction follows the direction of the U or V mapping coordinate on the object surface. The mapping channel used for this is explicitly specified.

G-BufferID override (-1=disabled) – If set to anything other than -1, this value overrides the 3ds Max gbuffer property. This allows you to set values outside of the 0-15 range permitted in the 3ds Max property.

Alpha mode – This override allows you to make the material show as always opaque (solid) or as always transparent in the alpha channel. By default its alpha value is derived from its opacity and refract components.

Propagate masks – Specifies the propagation of non-shading render elements (masks) after interaction with this material:

Never – Render elements are never propagated through this material of reflection occurs.
Through refraction – Render elements are propagated through this material if refraction occurs.
Always – Render elements are always propagated through this material, i.e. this material is never visible in masks.

Roughness mode – Allows choosing mode between roughness and glossiness.

IOR mode – Selects whether index of refraction (IOR) of base layer and clearcoat layer is set directly as IOR, or whether it is calculated from input Disney Specular value.

Base tail – Increases the tail of the base layer BSDF. The default value of 0 corresponds to the standard GGX BSDF. Increasing the value leads to longer tails (i.e. stronger reflection outside of the reflection peak).

Normals filtering – Determines how normal and bump maps are filtered:

None – No filtering is applied to normal and bump maps, providing high accuracy but potential noise and flickering.

Linear – Normal and bump maps are filtered linearly, just like other map types, potentially affecting material appearance with varying camera distance and render resolution. 

Roughness Modulation – Utilizes linear filtering for normal and bump maps while also adjusting material roughness to maintain consistent material appearance regardless of camera distance and render resolution. Default filtering method in Corona 11 and newer. 

Use complex IOR for metals

When enabled, the metal reflection is no longer specified by base and edge color. Instead of refraction, which is given by n(eta) and k (kappa). The complex index of refraction is specified per color channel.