Why keep the errant subtract-by-one? Zero is a legitimate value for FOF opacity, but as far as I can tell outside of one instance in P_FadeFakeFloor 256 isn't (and I think that's just a typo).
P_FadeFakeFloor and all its Specials do operate on the 1-256 range, so i just kept this inplace
However as far as i can see SRB2 did change those too at some point to be in 0-255 range
But i can remove the subrtract by one if wished
sorry somehow forgor about fixing this, but hope this should be fine now.
changed so P_FadeFakeFloor also operates on the 0-255 range so everything should (hopefully) be consistent now
