Action2/Vehicles
Introduction
Defining set-IDs for vehicles.
For features 0, 1, 2 and 3 (vehicles), Action2 is mainly used to define sets of sprites that show one vehicle in various states of load for one particular type of cargo.
Do not skip an Action2 using Action9 (unless it skips the whole file). Action2 must not be skipped by Action9 or TTDPatch will most likely crash. Skip or modify Action3 instead. Skipping an Action2 with an Action7 has no effect.
If there is only one load type, it is shown for all loads.
If there are two load types, the first is shown below 50%, the other above 50%. If there are three load types, they are shown above/below 33% and 66%. If there are four load types, they are shown above/below 25%, 50% and 75%, etc.
1.2 
Since OpenTTD r23080 you can use variable 10 to display different sprites in the GUI and on the map. Currently these cases are available:
| Lowest byte of variable 10 | Meaning |
|---|---|
| 00 | Vehicle is drawn in a viewport, i.e. on the map. |
| 01..0F | reserved |
| 10 | Vehicle is drawn in the depot GUI. |
| 11 | Vehicle is drawn in the vehicle details GUI. (This includes the refit GUI.) |
| 12 | Vehicle is drawn in the vehicle list. |
| 13..1F | reserved for other future GUIs. |
| 20 | Vehicle is drawn in the purchase list. (This includes the autoreplace GUI.) |
| 21 | Vehicle is drawn in the exclusive preview GUI or in the advertisement news. |
| 22..2F | reserved for other future GUIs with non-purchased vehicles. |
| 30..FF | reserved |
The other bytes of variable 10 are reserved, and must be masked. The cases 20..2F are called using the purchase-list chain (cargotype FF), the other cases are called for actual vehicles.
Syntax
For vehicles, the data looks as follows:
<Sprite-number> * <Length> 02 <veh-type> <set-id> <num-loadtypes> <num-loadingtypes> <loadtypes...>
| Element | Size | Description |
|---|---|---|
| <Sprite-number> | dec | A sequential sprite number |
| <length> | dec | The total number of bytes used in this action |
| 02 | B | Defines an action2 |
| <veh-type> | B | For what type of vehicle should the following sprites be used? |
| <set-id> | B | Set-ID of this action2 |
| <num-loadtypes> | B | Number of different states while moving |
| <num-loadingtypes> | B | Number of different states while loading/unloading |
| <loadtypes> | W | Sets from the most recent action1 to use for various states of loading. |
Description
Sprite-number
This is just the number you are at.
Length
Count the number of bytes in this action.
veh-type
This sets the type of vehicle that you wish to change. Set it to
00 for trains
01 for road vehicles
02 for ships
03 for planes
Set-id
This is the number that you give this set of sprites. You can choose any value between 00 and FF, and you can reuse them within a grf file at a later point (if being equal to an existing set-ID, the existing one is overwritten and the new one is used).
num-loadtypes
This is the number of different graphics that the vehicle has while it's not loading or unloading, depending on the amount of cargo it carries. For example, if it has two states, full or empty, this would be 02. If it has three states, full, half full or empty, this would be 03.
num-loadingtypes
Same as num-loadtypes, except this is used while the vehicle is loading or unloading. For example if the vehicle is closed, it might only have one state when moving (i.e. num-loadtypes is 01), but show several load states when it is being loaded or unloaded and thus open.
Neither num-loadtypes nor num-loadingtypes may be zero, there must be at least one state for each.
loadtypes
The sprite sets to use for the states of load. Each entry is a WORD value in little endian format, and refers to the most recent action1 sets. For example, action1 sets 4, 5 and 7 would be encoded as 04 00, 05 00 and 07 00, respectively. Note the additional 00 which is needed because it must be a word value here.
The first entries of these are used when not loading. There have to be num-loadtypes of these. After this follow the sets to use while loading/unloading, and there must be num-loadingtype of those.
Note that you can share action1 sets between several action2 entries. For example, you might have a wagon that can hold coal or iron ore, and it would look the same if it's empty. Then the empty sprite set could be shared by the action2 entries for iron ore and coal.
Example
Something to go here
