NML:Block syntax
Vehicles, Stations, Canals, Bridges, Towns, Houses, Industries (Tiles), Cargos, Airports+Tiles, Objects, Railtypes, Roadtypes, Tramtypes, Terrain
Syntax
In the description of the individual block types you'll often see a word enclosed by the less-than and greater-than symbols. These words should not be written literally, instead they reference to another block/item you should put there. The following words will be used:
- <literal-string>
- A string enclosed by quotes, for example
"this is a literal string" - <string>
- A string defined in the language file, for example
string(STR_GRF_NAME) - <expression>
- An expression, this can be a computation or single value constructed using <number>, <float>, <parameter>, <variable>, <function-call>
- <ID>
- The name of an item or block. IDs should start with a letter or underscore. The rest of the ID may consist of letters, underscores and numbers.
If something is enclosed by square brackets [] it's optional.
Available block types
Railtypetable / Roadtypetable / Tramtypetable
Overriding vehicles in other NewGRFs
Sorting vehicles in the purchase list
An example block
NML files are mainly composed from blocks. A block starts with the type of the block, optional arguments and then the contents enclosed by curly braces. Nearly all NML files will start with a grf-block. The grf-block takes no parameters and is one of the simplest blocks there is. Following is an example grf-block.
grf {
grfid : "AB\02\03";
name : string(STR_GRF_NAME);
desc : string(STR_GRF_DESCRIPTION);
version: 10;
min_compatible_version: 5;
}
Let's look at this code line for line.
grf {
This block is a grf-block. A grf-block has no parameters. The '{' is the start of the block content.
grfid : "AB\02\03";
This line sets the grfid of the resulting grf. The value is the letters AB followed by a byte with value 2 and then another one with value 3. The semicolon marks the end of the statement.
name : string(STR_GRF_NAME);
The name of the grf. In NML nearly all strings are put in language files. The format of the language files is described in another section. For now just assume a string with the name STR_GRF_NAME exists. To reference a string from the language file you use string(<stringname>) where <stringname> should be replaced by the actual name of the string.
desc : string(STR_GRF_DESCRIPTION);
This looks a lot like the previous line, only it sets the description instead of the name.
version : 10;
For a new grf you should set the version to 1. Every time you release a new version you should increase the version field by at least 1.
min_compatible_version : 5;
For a new NewGRF you should set the min_compatible_version to 1. Every time you change something in your newgrf which makes it incompatible to previous versions, you should set min_compatible_version to the current version. Changes which make a NewGRF incompatible to previous versions are most functional changes to existing behaviour, among others: changing vehicleIDs as well as some of their properties, changing industry layouts, railtype compatibility, changing (de-)activation conditions... Adding new, additional things and expanding existing behaviour (without changing the current one) is mostly considered safe).
}
This marks the end of the last-opened block, in this case the grf-block.
