Common Material Attributes#
The raytracer provides a set of physical materials which react realistically to lights when rendered with the path tracer integrator. Some are specialized for hair rendering or simulating specific types of materials, while some others can be of general use.
All materials can be connected to a network of texture operators to drive their physical attributes but also be combined in layers and blended together to accurately approximate real world materials while keeping rendering performance high.
Shared Attributes#
Most materials share a set of predefined attributes to control the sampling and the geometry approximation.
Material Sampling Overrides#
It is possible to override all material sampling settings directly at the material level instead of using the ones defined by the path tracer.
This is very handy, when you need to increase samples on specific materials while keeping others being sampled by the value defined in the path tracer.
For example, this can be used to disable multiple scattering on volumes or on the contrary, used to increase the number of bounces when simulating clouds.
Sidedness#
It is possible to specify the sidedness of a material. By default materials are considered as single sided surfaces. Shading normals follow the ones defined by the primitive. This is very important for the path tracer since depending on the material and the expected behavior, double sidedness can't be always assumed.
| Value | Description |
|---|---|
| Single | The material is considered as a single sided surface following the normal defined by the primitive. When seen from the other side the material is considered black. |
| Double | The material is considered as double sided surface. The normal of the primitive is always facing the direction of the ray. |
| Invert | The material is considered as a singled sided surface following the inverse of the normal defined by the primitive. |
Multiple Scattering#
Multiple scattering simulates the effect of the light bouncing on microfacets. It affects any rough diffuse, specular and transmissive surfaces. It is very important for photo-realistic results since it ensures energy conservation on rough materials which is why it is enabled by default.
However, it is still possible to control the intensity of the effect by modifying the Multiple Scattering Strength attribute.
All the renders below are rendered with multiple scattering disabled by setting Multiple Scattering Strength to 0%.
All the renders below are rendered with multiple scattering on by setting Multiple Scattering Strength to 100% (Default).
Opacity#
Surface opacity or transparency can be controlled using the Opacity attribute of the materials. For more information please reference to Transparency/Opacity section.
Transparent Shadows#
By default, the path tracer renders transparent shadows as well as an approximation of caustics. However using the Shadow Casting Mode attribute, it is possible to change how the path tracer manages shadows on transparent or transmissive/refractive materials directly at the material level.
| Shadow Casting Mode | Description |
|---|---|
| Opaque | The material is always considered opaque. |
| Physical | The material is always considered opaque but the opacity (transparency) is still affecting shadows. To get the full physical behavior, you must also set Refractive Caustics to Full. |
| Artistic | The behavior of shadows is artistically controlled using both Shadow Opacity and Shadow Coloring attributes. Shadow Opacity controls how opaque the shadows are while Shadow Coloring defines how much refraction/transmission and absorption colors affect the color of the shadow. |
| Pseudo-Caustics | Perform a cheap approximation of caustics by taking into account the surface properties such as refraction/transmission and color. |
Artistic#
In Artistic mode you get full control over Shadow Opacity and Shadow Coloring.
Shadow Opacity#
Shadow Coloring#
The renders below have the Shadow Opaciy set to 100%
Important
Refractive Caustics should only be activated when Shadow Casting Mode is set to Opaque (when Opacity is set to (1,1,1)), Physical or Artistic with Shadow Opacity at 100% and Shadow Color set to 0%. Enabling it on any other configurations will lead to render non physically correct caustics.
AOVs#
Materials can defined their own AOVs. They are either built-in in which case they'll appear in the AOV Editor or custom via the use of AOV Stores.
For more information about the AOV workflow of the raytracer, please refer to the AOVs section.
Light Path Expression Constants#
It is possible to declare Light Path Expression Constants to identify parts of a material shading network. This can be extremely useful to extract a specific texture graph in a AOVs using Light Path Expressions. For more information please refer to Light Path Expressions section.
Layering and Blending Materials#
Materials can be either layered to simulate a material made of multiple layers of surfaces such as a diffuse and a clear coat or blended together to create material composites.
Layered Material#
The Layered material can be used to simulate complex materials made of multiple layers such as car paints or plastics that have clear coat layer.
The idea is to define the properties of the layers such as their thickness to control how light is absorbed when traveling through the layers.
The material definition starts by the Base layer on which additional layers are added. The last one being the top most layer that is first hit by the light.
Two reflection layers with absorption simulating a car paint
Corresponding material network
This material is also really useful if you want to simulate a layer of dust on top of materials.
Material Blending#
The Blend and Multiblend materials allow you to mix different materials together. Unlike layered materials which simulate multiple layers of materials on which light is transmitted vertically from top to bottom, blend materials are material composites that mix their physical properties.
For example, blending a diffuse with an emitter will result to a diffuse material emitting light. The blend material supports masking so that it is possible simulate paint chips on a car paint for example.
Scratched paint material blending a layered material and a reflection material
Corresponding material network
