UE5 Mod Example

This project is a proof of concept for implementing modding support to an unreal engine project. This is by no means foolproof and meant as a POC. Type of modding may include custom assets, maps, and other assets. A good way to imagine it is like a DLC for your project. (As that is essentially what is happening) Project SDK can be found here: https://github.com/Ji-Rath/ModingExampleSDK

Creating a Mod

• Open the SDK project (If you are really picky, it can just be a blank project)
• Create a normal plugin
• Add any content that you would like (ensure the content is isolated and doesnt reference stuff like engine content)
• Package the plugin like DLC
• Find the .pak file in {ProjectName}/Plugins/{PluginName}/{Saved}/{StagedBuilds}/... (Keep on opening folders till you reach .pak file)

Where to Place Pak Files

Once the mod has been packaged into a .pak file, you must place it in the {ProjectName}/Plugins folder as that is where files are scanned. It has not been tested whether you can get away with placing them somewhere else.

Behind The Scenes

After our mod has been packaged into a .pak file, we can begin to import it into the project. This is done by using MountPakFile and RegisterMountPoint. An example is shown below:

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Accessing Assets

Currently, if you have packaged a map into a .pak and already mounted it, you can open it by using the console command: open /ModExternal/MapName (Assuming you have used the example above)

Additional Notes

• When creating a SDK of your project, consider leaving key blueprint files in the content folder so that modders may use them. Even better if you just give them the whole project.
• There are some specific settings you must follow when packaging (Both the mod and main game). Consider watching this video to ensure you are packaging correctly: https://www.youtube.com/watch?v=ndHNdUSRpho
• SDK Project needs to have Share Material Shader Code set to false in order for materials to work properly.
• Relevant classes: UPluginManager, UGameFeaturesSubsystem, IFileManager, UPakFileSubsystem

Planning

• Experiment with game features plugin
• Add examples which include spawning/replacing assets
• Add UI to load/unload specific mods

Research Notes

Game Feature Modding

• Using the Game Features plugin and placing mods in the exact path {ProjectName}/Plugins/GameFeatures makes things easier. This means you only have to mount the pak files in the plugin, register the mount point, and call UGameFeaturesSubsystem::LoadAndActivateGameFeaturePlugin.
  • This is because the project SDK where the mod is packaged is following the same path.
• Using the Game Features plugin to create modular plugins makes mounting much more difficult when not following the exact path. (For example, I want to place mods in {ProjectName}/Extensions rather than {ProjectName}/Plugins/GameFeatures). This is because when using UGameFeaturesSubsystem::LoadAndActivateGameFeaturePlugin, it tries to mount the plugin on its own. This results in the mount path being incorrect.
  • To solve this issue, disable ExplicitlyLoaded in the mod's .uplugin file.
  • Manually mount the plugin yourself. Then, mount the pak file, which will then take priority. Finally, call UGameFeaturesSubsystem::LoadAndActivateGameFeaturePlugin

Useful Sources

https://forums.unrealengine.com/t/inside-unreal-modular-game-features/242614/3 https://buckminsterfullerene02.github.io/dev-guide/ModSupport.html