Defining graphics set IDs.
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.
In general, the data looks as follows. Some features use a different syntax though (see table below).
<Sprite-number> * <Length> 02 <feature> <set-id> <num-ent1> <num-ent2> <entries...>
|<Sprite-number>||dec||A sequential sprite number|
|<length>||dec||The total number of bytes used in this action|
|02||B||Defines action 02|
|<feature>||B||For what type of feature should the following sprites be used?|
|<set-id>||B||What set-ID this action 2 defines|
|<num-ent1>||B||First number of entries, depends on feature|
|<num-ent2>||B||Second number of entries, depends on feature|
|<entries...>||W||Entry numbers, depends on the feature|
This is just the number you are at.
Count the number of bytes in this action.
This sets the type of feature that you wish to change. Set it to:
|07||Houses (special Sprite Layout format)|
|09||Industry Tiles (special Sprite Layout format)|
|0A||Industries (special Production Callback format)|
|0C||Sound Effects (callback failure only)|
|0E||Signals (callback failure only)|
|0F||Objects (special Sprite Layout format)|
|11||Airport Tiles (special Sprite Layout format)|
This defines the ID of the current action 2. This ID will later be referred to by action 3, or a variational/random action 2.
You can reuse action 2 IDs, and there's no restriction on the order in which they are defined.
Each feature has two different graphics ranges, but their exact meaning differs from feature to feature. For example, for vehicles, the first set is used while moving, and the second while loading/unloading in a station.
This is the list of action 1 sets to use, first num-ent1 for the first range, then num-ent2 entries for the second range.