Callback: Industry availability

Industry availability (22)

Called when TTDPatch needs to know if a given industry type is available.

This callback is intended for limiting your type as a whole, so you can't access any industry-specific variables, just the global ones. A good example for the use of this callback is a nuclear power plant that isn't allowed to appear before 1970.

GRFv7 For GRF version 7 and below the callback should return zero to make your type available, or any nonzero value to disable it.

GRFv8 For GRF version 8 and above the callback should return one of these values:

0000	Disallow construction
0001..00FF	Allow construction, and use the returned value as probability for appearance on the map. (Instead of using property 17 or 18.)
0100	Allow construction; use the appearance probability from property 17 resp. 18.

During this callback, variable 18 (extra callback info 2) can contain the following values:

Variable 18	Meaning
0	TTD is generating a map and needs to know if your type can appear.
1	TTD decided to build a new random industry during regular gameplay and needs to know if it can choose your type.
2	The user tries to build/prospect for your industry via the new industry window. TTD needs to know if the player is allowed to do this.