Since this is an enum, the added material should be added at the end i think, to not change the enumerations of the others.

How about `TILE_MATERIAL_OPAQUE` because it is closely related to `TILE_MATERIAL_LIQUID_OPAQUE`? Opaqueness is also the reason it is being added.

The default for alpha is 255, but i'm not sure any mod nodes other than liquids use the 'alpha' nodedef, they seem to use 'use texture alpha' instead. Also, semi-translucency is buggy in MT so not really usable on normal nodes. So perhaps this check is not needed?

maybe change `NDT_NODEBOX` as well?

why remove this?

This case could be combined with `case TILE_MATERIAL_LIQUID_OPAQUE:` a few lines below.