Callback: Station availability

Station/Rodstop availability (13)

This sets whether a station/roadstop can be constructed or not, i.e. whether it can be selected in the station construction window.  Returning 1 as callback return indicates the station can be built, and a return code of 0 removes the station from the selection.

GRFv≤7 Note that GRF versions 7 and lower only distinguished zero and non-zero return values.