FOCS Scripting Tutorial

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This tutorial covers how to modify FreeOrion Content Script (FOCS) files. For details on all of the possible values, see Effects.

All FOCS files are plain text files, though some contain extended characters, especially the language files.
Template:FOCS Notepad Notice

When a reference is made to the default/ directory, this refers to the Resources Files directory.
This directory varies on different systems and can be manually changed.
If you are unsure where this directory is, or want to change it:

Start FreeOrion
select Options
select the tab Directories (next to last)
see Resource Files.

On Windows this is typically 'C:\Freeorion\default\'
Be aware if you change it, you should likely copy the contents of the original default directory to the new location.

Creating a new entry

Create a new file in the default/scripting/buildings/ directory, name it TUTORIAL_ONE.focs.txt
BuildingType
    name = "BLD_TUTORIAL_ONE"
    description = "BLD_TUTORIAL_ONE_DESC"
    buildcost = 15
    buildtime = 1
    icon = ""

It is good practice to make sure the file ends with a blank line.

This creates a very basic building type that could be built anywhere but has no effect.

No player would be able to build this building however, as their empire does not know how.
For now, we will just give the knowledge to everyone at the start of the game:

Edit default/scripting/starting_unlocks/items.inf
Add the following line at the top
Item type = Building name = "BLD_TUTORIAL_ONE"

If you start the game now and select the production screen at your home planet, you will see:

ERROR: BLD_TUTORIAL_ONE

Hover over that and the tooltip shows:

ERROR: BLD_TUTORIAL_ONE_DESC

This is because we have not told the game what our building should be labelled as, just to use the key reference of BLD_TUTORIAL_ONE.
Just like the filename, key references could be named anything, regardless of what label we want to use.
The name entry in the definition needs to be unique, but description can be shared among other entries if needed.

The key references are looked up based on the language selected, in one of the stringtables.
You can start with the file that suits you best, for this example we will use the english file.

Edit default/stringtables/en.txt
Search for BLD_COL_SUPER_TEST_DESC
On the next blank line enter the following
BLD_TUTORIAL_ONE
A new building type from the scripting tutorial.

BLD_TUTORIAL_ONE_DESC
This is a brand new building type we just created.

Make sure there are blank lines before and after these new entries.

If you were going to share this entry with others, create the same entries in each of the other stringtable files as well. Few people are fluent in all of these languages, so simply copy the same text into the same spot in each file. If you can provide a translated version, please do as it cuts down on work others would need to do.

You now have a very basic building in the game, though it has no purpose.

Entry Files

All of the FOCS entry files have a double extension of .focs.txt.
These files will be loaded regardless of the rest of their filename, or how deeply nested in the sub-directory they are.

Some special entry files have the extension .inf.
While most of these files can be freely edited, they can not be renamed or moved.

Any other file extension is not loaded into the game, unless an entry file specifically includes it.
The extension .macros is commonly used to denote scripting macros used in various entry files.
Entries that are not wanted in the game currently, but kept around for reference, are typically given the extension .disabled.

Entry files should never #include a file with another entry definition in it.

Directory Structure

Entry files are categorized by their type and should remain within the directory for that type(nested sub-directories are ok).
For example Tech entries can be anywhere in default/scripting/techs/, but should never be in default/scripting/fields/.
This only applies to the actual definition files, those with the extension .focs.txt.

The following directories within default/scripting are for .focs.txt entries:

alignments/ Alignment entries
buildings/ Building entries
empire_statistics/ Empire statistics entries
encyclopedia/ Encyclopedia topic entries
fields/ Field entries
monster_designs/ Ship loadout designs for space monsters
ship_designs/ Ship loadout design entries
ship_hulls/ Ship hull designs
ship_parts/ Ship part entries
specials/ Entries for specials
species/ Species entries
techs/ Tech entries

Required files

These are relative to default/scripting/:

keymaps.inf To Be Determined - Default keymap values
monster_fleets.inf Entries for monster fleets
starting_unlocks/buldings.inf Buildings pre-built on every starting homeworld.
starting_unlocks/fleets.inf Entries for fleets every player starts the game with.
starting_unlocks/items.inf Blueprints available at the start of the game to every player. For techs this means they are completed, for other types it allows the player to produce them.
techs/Categories.inf Categories that a tech must belong to. For now these should not be changed or added to, aside from possibly the graphic or colour definitions.

Additionally, definitions listed in any starting_unlocks/ file or monster_fleets.inf need to be avaiable.
The default AI may assume any or all of the default entries to exist.

Macros

A basic macro definition looks like this:

FIRST_ONE
'''2'''

The three apostrophies denote preformatted text, meaning any newlines are part of the macro.
Macro names should be in all uppercase, with underscores in place of spaces. They should also be uniquely named.

References to a macro are done by adding double brackets:

buildtime = [[FIRST_ONE]]

The game will end up seeing this as buildtime = 2

Macros may also use arguments:

NEW_MACRO
'''@[email protected] * @[email protected]'''
Multiplies the first argument by the second.
[[NEW_MACRO(2,3)]]
Results in 6 (2 * 3)

You can pass other macros for the arguments:

[[NEW_MACRO(FIRST_ONE,4)]]
Results in 8 (2 * 4)

Macros are mainly used to keep consistant values for multiple definitions.
When this is the case, it is best to have the macro definition in a file by itself, so other files can include it.
Sometimes macros are used for a complicated formula to help the readablity of the file. There is no need for these macro definitions to be separated if they are never used in another definition.

Including other files

Files are usually included for macro definitions.
You can include another file with the #include directive:

#include "some_file.macros"
Includes the file named some_file.macros

The directive should by on a line by itself, without any spaces before #include. There is no restriction on what files are included, however you should not include files containing another FOCS entry in it. This would lead to a conflict when the entry is loaded twice.

Troubleshooting

If the entry is in the game, but does not show the name or the description correctly, check the stringtable entry for your selected language.

Typically if there is a problem with the game parsing an entry, it will show the error in the console window. The error will also be in the log file freeorion.log, which is located in your user directory (Options > Directories > Save files (parent directory))

If there are no errors shown, you can make sure the file is loading by setting the log level to TRACE.
Either edit the config.xml file in your user directory or launch the game with the --log-level TRACE argument.
The client log file (freeorion.log) will now show each file as it was loaded in, as well as any files that were skipped.

If you need further help, post a question in the forums.