Callback: Station slope check
Land slope check (149/157)
This callback is called for each tile where the new station part will be built. It can return zero to accept the current tile or one to make the station building fail with the "Land sloped in wrong direction" error message. Other return values are reserved for future use, don't use them for now.
Since the station isn't built yet, no 8x variables can be accessed. Only variables 43 and 67 will work from the 4x and 6x variables. You get the following information, though:
- variable 18:
| bit numbers | Meaning |
|---|---|
| 0..7 | offset of current tile on the platform, 0 is the northmost tile |
| 8..15 | bits 8..15: current platform number, 0 is the northmost platform |
| 16..23 | total length of station being built |
| 24..31 | total number of platforms being built |
- variable 10:
| bit numbers | Meaning |
|---|---|
| 4..7 | Slope info of the current tile:
|
| 0..3 | the same information, but "mirrored" (bit 0 and 2 swapped) if the station is built in the NW-SE orientation. This allows you to check slopes without checking the orientation explicitly. |
| other bits | reserved for future use |
The callback is called only after the normal checks TTD does for slopes, so it's not possible
to allow a slope that isn't allowed by default; you can only narrow the set of allowed slopes. If the callback fails, the tile will be accepted. It is, however, called for flat tiles, so you can force your station to sloped land. You can't access the station info even if the platform is added to an existing rail station or is overbuilding station tiles. That's because TTD will decide this later in the code, after the slope is already accepted.
This is called if available just before object construction, it does not require that any flags be set in the action0.
Please note that for Objects only the low byte of variable 18 is valid (Offset from north tile (origin), stored as YX) and that variable 10 does not have the reversed version, and bits 0 - 3 contain the actual raised corners (same order as bits 4 - 7).
