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A Base Material is required. But the next layer does not need to be in sequence. In other words, you could connect a layer to Layer 2 without connecting to Layer 1. This adds flexibility for the look development workflow should you need to add/remove or re-order layers.
Connect a PxrLayer that is for the base layer. This is your base or bottom layer like glass, metal, skin, wood, etc. Other layers are on top of this base layer.
This turns the layer on and off. If off, this layer will not render.
Connection to a PxrLayer that is for layer 1. This is where you connect your material layer like glass, label, dirt, etc.
Layer 1 Mask
Mask for this layer 1. Values closer to zero will apply less of this layer. A value of 0.0 is off or invisible while 1.0 is on or completely visible.
Layers 2 to 4
These use the same controls as described above.