Model materials
Predict Matter supports a few models of materials. These models are not physical materials and must not be used for iso-photography rendering. They are mainly used for scenery, decorative elements, debugging or for the materials you could not measure.
The supported models are :
Lambert : the material reflects light with the same reflection coefficient in all directions : it is a purely matte material, defined by the spectrum of the light it reflects. See the Spectrums section for more details on spectrums.
Examples of Lambert materials
Phong : the material is defined by a color (or a texture of colors) and an exponent that defines how glossy the material is. The higher the exponent is, the glossier the material will be (see example bellow).
Examples of textured Phong materials
Examples of Phong materials with varying exponents : from left to right, e=[0.1, 1, 8, 32, 64, 512]
Oren Nayar : the material is defined by an albedo that defines the diffuse aspect of the material, and a roughness that defines how glossy the material is.
Examples of Oren Nayar materials
Kubelka Munk : the material is defined by two constants (K and S) that define the absorption and the diffuse reflection of the material. See the Spectrums section for more details on spectrums.
Examples of Kubelka Munk materials
Shadow Catcher : the material is transparent but it will catch shadows induced by the environment in the scene. This can be useful to display shadows on the floor of a skybox for instance. The shadows induced by the Shadow Catcher will only be visible when looking at them directly : they won't be visible on the reflection of a mirror for instance.
The Shadow Catcher material only works when there is an HDRI environment in the scene. If there is no environment in the scene, the shadow catcher will be ignored and won't cast shadows.
The Shadow Catcher material has its own type because it is a very specific material : it does not model an actual diffuse material but only mimic shadows on a surface that should not exist otherwise.
In the Predictive Matter shaders, matte materials (Lambert, Oren Nayar, Kubelka Munk) and specular materials (Phong) are treated differently and correspond to 2 different shaders : "Matte" and "Phong".