The tutorial covers: A custom shader in Mari that replicates our in-game physically based shader nearly identically. Paint diffuse, normal, specular, and roughness to describe any type of material simultaneously by using shared mask layers. Everything gets baked down to one material draw call.
Adjusting the brightness of the paint’s roughness map on the fire hydrant will transition through mips in the specular cubemap, effectively “blurring” the reflection. This can be seen more clearly on the example using the chrome sphere. Using the mask of rust as an input to the bump channel, painting rust will also affect the final normal map.