What are Layer Variables

Output and input layer variables that connect a LayerShader to the layer system.

Layer variables are the variables that connect a LayerShader to the layer system. They're divided into two groups:

Output variables: written by the shader to pass material properties up the chain - LAYER_OUT_ALBEDO, LAYER_OUT_ROUGHNESS etc.
Input variables: read from other layers in the chain - LAYER_BELOW_* reads the layer below, LAYER_BLEND_* reads the Blend layer in a mask.

Each LayerShader type has its own set of variables. See the SurfaceShader, MaskShader, OverlayShader and DataShader references for the full lists.