Hey Cyclopropinon,
Sodium has its own code for defining the transparency of each block, so the opacity changes that Wurst makes to the vanilla / Indigo renderer have no effect when using Sodium. I have looked into this and it seems like there is no place in Sodium's code that I could target with a mixin without adding Sodium as a dependency of Wurst.
Mixin support for non-dependencies (i.e. code that might not actually exist at runtime) is extremely limited. I would basically need to find a method in Sodium that can access the rendered BlockPos and BlockState, as well as the color of the currently rendered quad, while not relying on any Sodium-specific objects (not even that same quad that it needs to manage the color). As far as I can tell, this is impossible.
What I could try is to make a separate Sodium-Wurst compatibility mod, which would have both Sodium and Wurst as dependencies. This mod could then mixin into Sodium's BlockRenderer without any limitations and make Opacity X-Ray work, as long as Fabric API, Wurst, Sodium, and that compatibility mod are all installed in the mods folder.
I'm not sure how many people would use this compatibility mod, as it makes the installation process a bit more complicated, but it could be an interesting experiment to just make it and see what happens.
