Attention: Here be dragons
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Exporting packs, patches, and mods
Use cases
Oftentimes, one would like to add functionality to one's game after it has been deployed.
Examples of this include...
Downloadable Content: the ability to add features and content to one's game.
Patches: the ability to fix a bug that is present in a shipped product.
Mods: grant other people the ability to create content for one's game.
These tools help developers to extend their development beyond the initial release.
Overview of PCK/ZIP files
Godot enables this via a feature called resource packs (PCK files,
with the .pck extension, or ZIP files).
Advantages:
incremental updates/patches
offer DLCs
offer mod support
no source code disclosure needed for mods
more modular project structure
users don't have to replace the entire game
The first part of using them involves exporting and delivering the project to players. Then, when one wants to add functionality or content later on, they just deliver the updates via PCK/ZIP files to the users.
PCK/ZIP files usually contain, but are not limited to:
scripts
scenes
shaders
models
textures
sound effects
music
any other asset suitable for import into the game
The PCK/ZIP files can even be an entirely different Godot project, which the original game loads in at runtime.
It is possible to load both PCK and ZIP files as additional packs at the same time. See PCK versus ZIP pack file formats for a comparison of the two formats.
See also
If you want to load loose files at runtime (not packed in a PCK or ZIP by Godot), consider using Runtime file loading and saving instead. This is useful for loading user-generated content that is not made with Godot, without requiring users to pack their mods into a specific file format.
The downside of this approach is that it's less transparent to the game logic, as it will not benefit from the same resource management as PCK/ZIP files.
Generating PCK files
In order to pack all resources of a project into a PCK file, open the project and go to Project > Export and click on Export PCK/ZIP. Also, make sure to have an export preset selected while doing so.
Another method would be to export from the command line
with --export-pack. The output file must with a .pck or .zip
file extension. The export process will build that type of file for the
chosen platform.
Note
If one wishes to support mods for their game, they will need their users to create similarly exported files. Assuming the original game expects a certain structure for the PCK's resources and/or a certain interface for its scripts, then either...
The developer must publicize documentation of these expected structures/ interfaces, expect modders to install Godot Engine, and then also expect those modders to conform to the documentation's defined API when building mod content for the game (so that it will work). Users would then use Godot's built in exporting tools to create a PCK file, as detailed above.
The developer uses Godot to build a GUI tool for adding their exact API content to a project. This Godot tool must either run on a tools-enabled build of the engine or have access to one (distributed alongside or perhaps in the original game's files). The tool can then use the Godot executable to export a PCK file from the command line with OS.execute(). The game itself shouldn't use a tool-build of the engine (for security), so it's best to keep the modding tool and game separate.
Opening PCK or ZIP files at runtime
To load a PCK or ZIP file, one uses the ProjectSettings singleton. The following
example expects a mod.pck file in the directory of the game's executable.
The PCK or ZIP file contains a mod_scene.tscn test scene in its root.
func _your_function():
# This could fail if, for example, mod.pck cannot be found.
var success = ProjectSettings.load_resource_pack(OS.get_executable_path().get_base_dir().path_join("mod.pck"))
if success:
# Now one can use the assets as if they had them in the project from the start.
var imported_scene = load("res://mod_scene.tscn")
private void YourFunction()
{
// This could fail if, for example, mod.pck cannot be found.
var success = ProjectSettings.LoadResourcePack(OS.get_executable_path().get_base_dir().path_join("mod.pck));
if (success)
{
// Now one can use the assets as if they had them in the project from the start.
var importedScene = (PackedScene)ResourceLoader.Load("res://mod_scene.tscn");
}
}
Warning
By default, if you import a file with the same file path/name as one you already have in your project, the imported one will replace it. This is something to watch out for when creating DLC or mods. You can solve this problem by using a tool that isolates mods to a specific mods subfolder.
However, it is also a way of creating patches for one's own game. A PCK/ZIP file of this kind can fix the content of a previously loaded PCK/ZIP (therefore, the order in which packs are loaded matters).
To opt out of this behavior, pass false as the second argument to
ProjectSettings.load_resource_pack().
Note
For a C# project, you need to build the DLL and place it in the project directory first.
Then, before loading the resource pack, you need to load its DLL as follows:
Assembly.LoadFile("mod.dll")
Troubleshooting
If you are loading a resource pack and are not noticing any changes, it may be due to the pack being loaded too late. This is particularly the case with menu scenes that may preload other scenes using preload(). This means that loading a pack in the menu will not affect the other scene that was already preloaded.
To avoid this, you need to load the pack as early as possible.
To do so, create a new autoload script and
call ProjectSettings.load_resource_pack()
in the autoload script's _init() function, rather than _enter_tree()
or _ready().
Summary
This tutorial explains how to add mods, patches, or DLC to a game. The most important thing is to identify how one plans to distribute future content for their game and develop a workflow that is customized for that purpose. Godot should make that process smooth regardless of which route a developer pursues.