Each slot requires at least one overlay set but usually receives a list of them. Overlays carries all the necessary textures to generate the final material(s) and might have extra information on how they are mapped. The first overlay in the list provides the base textures, and all other overlays included are combined with the first one, in sequence, generating the final atlas.
UMA standard uma material (UMA_Diffuse_Normal_Metallic) requires three textures provided by overlays, one texture for Albedo/Diffuse color, one texture for Normal map, and Metallic/Roughness.
Overlay Name - Name the UMA system will use to refer to this overlay. This should be unique!
Overlay Type - Normal or Cutout overlay type. This determines whether or not to use a cutout shader during the texture merging process.
Rect - (Optional/Empty) Destination rectangle for drawing overlay textures.
Alpha Mask - (Optional) Alpha mask, if alpha mask is not set the texture.alpha is used instead.
Texture List - Array of textures required for the overlay material.
Tags - (Optional) Use this to identify what kind of overlay this is and what it fits. Not used by UMA internally.
Material - The UMA Material this overlay uses.
Occlusion Entries - For use with UMA Powertools.
Each overlay can modify it’s color multiplicatively or additively. This can be used to tint overlays, such as having a skin texture that can be tinted to different skin tones. Overlays can be layered on top of each other to selectively color parts of the final output.
Multiple overlays on the same slot can work together by being layered on top of each other to achieve advanced effects.
For example, having a custom eye color. The color multiplier shouldn't change all of the eye, only the iris, so we have the base texture of the entire eye, and then layed over top of that is the iris texture where only the iris is opaque and the rest transparent (so the base texture is visible). Then the iris texture gets the color modification.
A new overlay asset can be created by right clicking and selecting “Create→UMA→Core→Overlay Asset”