Texture Usage in Materials
Most opaque Materials should only need BaseColor, Roughness, and Normal to come from textures. Specular should not be specified
and Metallic can be a constant. Given that base set of Material properties, most Materials that only have one layer should use
the following setup which only requires two textures:
BaseColor in RGB
Roughness in alpha
Normal map in RGB
Additional layers will need to use more textures, with the option of only layering in BaseColor + Roughness to avoid multiple normal map texture fetches.