The Substrate documentation says that only the Slab and Clear Coat BSDFs can use the Substrate Operator nodes. However the Unlit BSDF seems to work correctly with the Coverage Weight Operator. Is this how Unlit Transparent materials should be made? The Coverage Weight Operator isn’t required to get the same output, but it’s a more intuitive way of making the material translucent.
For example if I want to create a simple material with an alpha along the U gradient, I can use only the Unlit BSDF, but I have to invert the mask before passing it into the Transmittance Color:
Additionally, if I want the emissive color to use the same alpha, I have to explicitly multiply it by the inverted alpha before passing it into Emissive Color:
Otherwise it will not respect the intended alpha:
Using the Coverage Weight operator simplifies all of this because all I have to do to define the translucency is plug my alpha into the coverage weight, and define my material without the alpha on the Unlit BSDF (keeping Transmittance Color 0):
The Substrate stats window shows that the Coverage Weight material has a higher cost than the BSDF alone, but there is no difference in the “Fully Simplified” section, which has stats identical to the BSDF-only material.
Coverage Weight material:
BSDF-only material:
If this means that ultimately they compile down to the same thing then using Coverage Weight simply makes the material more intuitive to create because it works like a classic opacity value; the alpha doesn’t have to be inverted, and it works on all properties of the BSDF. However, it makes the Transmittance Color useless, so I’m wondering what the intended approach is for creating simple materials like this.