Mixer is built upon the Physically-Based Rendering (PBR) process.

Differentiating PBR from other rendering processes, it ensures energy conservation, is based on the microfacet surface model, and uses a physically-based BRDF (bidirectional reflectance distribution function).

  • Energy must be conserved – the amount of light reflected off the object must be lower or equal to the amount of light that hit the object.
  • The idea behind the microfacet surface model is that surfaces are generally not completely smooth, and hence have microfacets that affect the reflection of light.
  • The BRDF is a function that defines how a ray of light interacts with a surface based on its component maps.

In the context of Mixer’s implementation of PBR, Mixer supports one workflow for now i.e Metalness. Mixer will convert your project made in specular workflow previously into metalness workflow. However Mixer provides you the ability to convert maps made in metalness workflow into specular. You can also view specular workflows maps like diffuse, gloss and specular in the render mode.

Maps

Each material has a set of maps that the BRDF uses to determine how a ray of light will interact. Each map’s values are used differently.

Albedo Used in the metalness workflow, this map contains the color information of the surface.
Metallic Used in the metalness workflow, this greyscale map contains the metallicity of the surface. A metallic surface’s specular reflection is created with color information from the Albedo map. A nonmetal will use color information from the light. The more metallic a surface, the higher the intensity of specular reflections.
Diffuse Used in the specular workflow, this map contains the color information for diffuse reflections. While often similar to or the same as the albedo map, this can sometimes also contain baked shadows.
Specular Used in the specular workflow, this map contains the color and intensity information for specular reflections.

Gloss/Roughness

A greyscale map that determines how rough or smooth a surface is. Both maps contain the inverses of the same information. A rough surface will have a larger specular reflection width, where a smoother surface would have a sharper specular reflection.

It is important to note that metallicity and glossiness are not the same. There can be rough metals, and smooth non-metals. The following image illustrates this:

Brian Karis,
Brian Karis, "Real Shading in Unreal Engine 4". Epic Games, 2013.

Additional Maps

There are also other maps that are commonly used and are supported by Mixer.

Normal

The normal map holds the normal vector for each pixel on the surface. This is used for light reflection calculations. This is often used to create imperfections on the surface, simulating lighting without changing the geometry of the surface.

Displacement

A greyscale map that determines how much the surface is displaced along the normal. Used alongside the normal map, this can be used by engines or renderers to actually displace the geometry for more realistic depth.

Occlusion

A greyscale map that holds information for occluded areas to create shadows. These shadows add extra detail to the darker areas of your surface.

Curvature:

A curvature map stores the convexity/concavity of the mesh. Also called Concavity, Convexity, Pits & Peaks, Worn Edge.

For more information on PBR, see the following links:

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