Add mod-support to your Unreal Engine 4 Game

Introduction

I will be running you through the process of setting up a mod (or “User Generated Content”) for your Unreal Engine 4 game. I’ve created a sample FPS project with a simple mod included, it’s available for download on GitHub. As a base I used the Blueprint FPS Template. The mod changes the weapon behavior by shooting three balls in an arc instead of one. The Mod source contains a gamemode, map and custom player character.

Mods are handled as Plugins by the engine, so I recommend reading up on how plugins are handled by the editor before moving on.

This guide and the mod sample on Github were built using UE 4.9 Preview 4. There are some issues with cooking & packaging in earlier releases.

Warning: This procedure is intended for early adopters only! The pipeline may change and will receive improvements as it’s still work-in-progress.

The Project

The full example project is available for download on GitHub. It’s based on the FPS Blueprint Template with a ./Plugins/MyFirstMod folder containing our custom content.

mods_header_narrow

Creating the mod

To create a mod, you must create a Plugin. As mods (or UGC – “User Generated Content”) are handled as Plugins by the engine. Below is the folder layout for ModSampleGame. The ./Plugins/MyFirstMod/ contains a /Content/ folder and a .uplugin descriptor file. The descriptor is loaded by the editor and can be hand-edited using any text editor. The /Saved/ folder is created by the cooking process.

mods_pluginsfolder

Plugin Descriptor

The contents of the descriptor can be edited manually, here is an example of its contents:

{
"FileVersion" : 3,
"FriendlyName" : "MyFirstMod",
"Version" : 1,
"VersionName" : "1.0",
"CreatedBy" : "Tom Looman",
"CreatedByURL" : "http://www.tomlooman.com",
"EngineVersion" : "4.9.0",
"Description" : "My First Mod",
"Category" : "User Mod",
"EnabledByDefault" : true,
"Modules" :
[
],
"CanContainContent" : true
}

You can use this example and paste it into a new .uplugin file for creating your own mods.

Plugin Content

To view and edit UGC or mod content, make sure you enable “Show Plugin Content” in your Content Browser under “View Options” in the bottom right corner. In the sample project from GitHub you should see MyFirstMod as one of the listed Plugins.

mods_contentbrowsersettings

Setup Launcher Profiles

mods_projectlauncheroverview

To open the launcher (for packaging of the game and mod) go to Window -> Project Launcher. At the bottom of the Project Launcher window click the “+” symbol to create your new custom profile. We will need two profiles, one for the base game build, and another for our user mod.

Important note: As of right now the profiles don’t ship with the project files, but are stored in AppData/Local/UnrealEngine/4.9/Saved/Launcher/. Please use the guide below to setup the profiles.

Full Game Profile

First we must create a base game build. Mod creators would not need this profile, this is only intended for the developer of the game.

The project is set to “ModSampleGame”, using the default AnyProject works just fine too. The “Do you wish to build?” is checked and build configuration for this example is set to “Development” for testing purposes. Normally you’d want to set this to Shipping, however we need to have console commands available to try out our mod. Please keep this in mind for your own project profiles.

mods_fullgamecook_01

First set the cooking dropdown to “By the book” to enable the other options for the Cooking category. For this example we only cook for WindowsNoEditor, using the “en”-culture. We’re making a game release so we check “Create a release version of the game for distribution” with the release name of “1.0”. Please make sure the other checkboxes match from the image below.

mods_fullgamecook_02

We don’t need to deploy and/or remotely store our package:

mods_fullgamecook_03

Now you have setup your full game profile, make sure to add an appropriate name such as “FullGame Release v1.0” with an accurate description. We won’t be running the profile just yet as we will first setup our MyFirstMod profile.

MyFirstMod Profile

This profile is only slightly different from the full game profile. With “build dlc” enabled instead of a new game release. Each mod would have a different profile to package its contents.

The first part is equal to the FullGame:

mods_firstmod_01

As you can see, there are some changes to the Cook options below. The “build dlc” is a little confusingly labeled as it’s looking for content in the /Plugins/ folder. Make sure you enter the name for the mod to build, this must be the same as the folder name of your /Plugins/<ModName>, in the case in our example MyFirstMod. The option “Include engine content” must be disabled. We only want to include whatever is inside our mod folder, if you need engine content you should copy over the content to the Plugins/ModName/ folder instead.

mods_firstmod_02

The third section is the same as the full game, we do not copy to any repository and don’t deploy to a device.

mods_firstmod_03

Cooking your first mod

First cook our FullGame profile, and repeat the process for the MyFirstMod profile by pressing the Launch key for both, pressing “Done” after the run completes, and repeating for the second profile.

mods_cookprofiles

FullGame cook is located at: ModSampleGame/Saved/StagedBuilds/ You can move this anywhere on your disk.

MyFirstMod is located at: ModSampleGame/Plugins/MyFirstMod/Saved/StagedBuilds/WindowsNoEditor/ModSampleGame/Content/Paks/

You can rename the .pak file of the mod so we can move it to our full game ModSampleGame/Content/Paks/ folder. For an example see the included packaged project source from GitHub: PackagedSampleGame/ModSampleGame/Content/Paks/

Loading a mod

By default additional .pak files are automatically loaded by the game when placed in the /Content/Paks/ folder of your cooked game. You can use a sub-folders (for example “./Content/Paks/Mods/”) to organize your custom content. They will still be loaded automatically. In the example below I manually renamed the generated .pak file from the MyFirstMod profile to “MyFirstMod.pak”.

mods_cookedpakfolder

To test if our mod was loaded successfully, open the console window using Tilde (~) and type “open modexamplemap” you should now be respawned into our custom level, with our custom player that fires three projectiles instead of one when firing the weapon using the left-mouse button.

mods_modexample

Done!

Now you’ve seen the process of setting up your first mod for an Unreal Engine 4 game! The pipeline is still a work in progress and will be smoothed out in upcoming engine releases. Now you have a basic pipeline to get you started for UGC support in your own project.

Please leave your feedback! We’re in the process of improving the pipeline and adding more features to make modding with Unreal Engine 4 as awesome as it can be, leave your comments.

References

21 Comments

  1. In the code you can use something like this:

    TArray<TSharedRef > Plugins = IPluginManager::Get().GetDiscoveredPlugins();

    for (int32 i = 0; i < Plugins.Num(); i++)
    {
    const TSharedRef &Plugin = Plugins[i];

    const FPluginDescriptor& PluginDescriptor = Plugin->GetDescriptor();
    if (PluginDescriptor.Category == TEXT(“User Mod”))

    but there is another question, how to find cooked levels in a plugin? So far I think it is impossible without external mod descriptor.

    • Interesting thanks! Although that is very prone to user error since categories are not enforced by the engine. I’m following up with the team at Epic to improve the pipeline, I’ll forward these two issues as well.

      Cheers,

      Tom

    • It would be nice if engine has ability to create mod plugins with predefined settings same as you wrote in this tutorial.
      This can be achieved in a SNewPluginWizard, the SNewPluginWizard can be expanded with new FPluginTemplateDescription.

    • You should check Engine\Programs\AutomationTool\Saved\Logs\ directory, there are usually more info about potential problems with AutiomationTool.

  2. Awesome article, thank you! As I understand, we have to:
    1. Enable plugin before build game;
    2. Restrict maps by adding [AllMaps] section to DefaultEngine.ini.
    for this approach to work.

    Is there any way do the same thing when game builds without knowledge of any plugin, and plugin builds later so dlc pak-file goes to end-user who already have basic game build? I’ve downloaded your example, and ModSampleGame-WindowsNoEditor.pak contains reference to MyFirstMod.uplugin. Does it means that we can’t build DLCs after game release was shipped?

    • Hi Alex,

      Hmm that must be an issue on the packaging end I bet, you should absolutely be able to do DLC/plugins later, not sure why it maintained that reference to the .uplugin (may be a side-effect of it loading by default? I’m not sure). One recommendation I have heard (for DLC) is to keep all DLC content in your base game (maintained with updates) and only use DLC pak’s to ‘unlock’ that content, it’s the easier way to prevent a build hell with maintaining tons of builds and patches for different DLCs etc. as it all becomes one.

      – Tom

    • Not in the foreseeable future I’m afraid. Perhaps when I get far enough into a project to tackle those issues myself 🙂

      – Tom

  3. thank you for this tutorial
    i have a problem,my pak file could not load by game autoly,
    i tried to put your pak file to Content\Paks directory.your file was loaded.i guess there must be something i missed
    could you help me?

  4. Great article, thanks! Tom, I’m looking for a way to load maps (and content) from pak files at run-time, in mobile devices. Do you think this approach could be used to achieve that?

    • You could load maps at runtime from separate .pak files yes. I remember UE3 had a feature to automatically download new map files during load screens, I don’t know if this exists for UE4 as well unfortunately.

      – Tom

  5. Hello Tom, Thanks for your tutorial, i want to ask a question in case that we have two or more .pak file, how we can manage mounting order ? (I know in launcher it’ll replace _p.pak and it’s included previous .pak)…
    For example : I’ve separated textures, materials and meshes .pak file, i want to mount them in order of textures first and then materials and finally meshes.

    Thank you again

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