Modular Game Features: What you need to know

The Modular Game Feature system is a new addition to Unreal Engine 4.27 and Unreal Engine 5 that allow developers to author standalone features for their projects.

These standalone features help compartmentalize Unreal projects, thus keeping the codebase clean and readable. And due to the nature of a modular game feature, these will help avoid accidental dependencies.

The essential aspects of this system are —

• Easily inject new content into an existing project
• The core game is entirely unaware of its existence
• Dynamically loadable and unloadable without breaking the game

In this article, I will be going over what you need to know to get up and running with the Modular Game Feature system in Unreal Engine.

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Requirements

Important notes

Here are critical aspects to know when you're implementing a new Game Feature —

• Game Features are essentially project-specific plugins
• Game Features can be moved to other projects
• Game Features should reference plugins it requires
• Game Features should not be referenced by the base game itself
• Game Features can contain content and/or code
• Game Features are required to be placed under /{ProjectName}/Plugins/GameFeatures/*
• Game Features can be configured via the Data Asset found within the root folder of the Game Feature
• Game Features will activate for everyone within a multiplayer session

C++ Notes

Important notes that are C++-specific

• #include "GameFeaturesSubsystem.h" is the required include
• GameFeatures must be included in the Build.cs file for the project or plugin

using UnrealBuildTool;
 
public class UDR_ModularGameplay : ModuleRules
{
	public UDR_ModularGameplay(ReadOnlyTargetRules Target) : base(Target)
	{
		PCHUsage = PCHUsageMode.UseExplicitOrSharedPCHs;
 
		PublicDependencyModuleNames.AddRange(new string[] {
			"Core",
			"CoreUObject",
			"Engine",
			"InputCore",
			"GameFeatures"
		});
 
		PrivateDependencyModuleNames.AddRange(new string[] {  });
	}
}

Creating a Game Feature plugin

1. Enable the Required Plugins

Before you can create a Game Feature, you must enable the following two required plugins —

• Game Features
• Modular Gameplay

Once these two plugins have been enabled, restart the editor.

2. Add entry to PrimaryAssetTypesToScan

Once the editor has been restarted, you will receive a message in your message log stating the following —

Adding this entry is required for the engine to acknowledge the Primary Asset Type associated with the Game Modules.

To fix this issue, follow either the automated or manual method below.

Note: If this message doesn't appear in your Message Log, you can skip this step

3. Creating the Plugin

Opening the Game Feature configuration window

The Game Feature configuration window automatically opens after it has been created. To find and open the configuration window manually —

Configuring the Game Feature

With the Game Feature configuration window opened, you will find three primary categories —

1. Feature State
2. Actions
3. Game Feature

Each of these plays a vital role in setting up and defining the game feature itself.

Feature State

The Feature State category controls the initial and current state of the Game Feature. The state of a Game Feature is divided into four options – Installed, Registered, Loaded, and Active.

Actions

The Actions category defines what actions occur when the Game Feature is enabled or disabled.

Here are the actions that are currently available as of Unreal Engine 5 Early Access 2 —

Add Cheats

The Add Cheats action allows developers to easily add their own debug commands via registering a Cheat Manager Extension with the game.

Cheats are purely for debugging and will not be included in shipping builds.

Add Components

The Add Components action will add a component to the designated actor class if it has been registered to receive components via the Game Framework Component Manager.

There are four options within the action —

Adding an actor as a Receiver

By default, actors have to be added as receivers to receive Game Feature Components. This step is generally done via BeginPlay.

Depending on the component and needs, consider using C++ to add the receiver during an earlier phase.

BlueprintC++

Removing an actor as a Receiver

It is ideal to clean up and remove the actor from being a Game Feature Component receiver during the Destroyed or EndPlay events.

Note: **When an actor is removed as being a receiver, it will automatically remove the Game Feature Components added. There is no need to do that manually.

BlueprintC++

Add Data Registry

The Add Data Registry Action will add a Data Registry to your project.

Add Data Registry source

The Add Data Registry Source will add a data source that will stream intoa Data Registry.

• Each configures the path to each data source must be configured

Custom Actions

An example of what other actions can be added manually via C++. Some, if not all, will be available when Unreal Engine 5 fully releases.

You can find these in the Valley of the Ancients demo.

• Add Abilities
• Add Attributes Defaults
• Add Input Mapping
• Add Level Instances
• Add Spawned Actors
• Add World Systems

Asset Manager

The Asset Manager category is utilized to tell the engine that new assets are available. For example, introducingnew weapons or items to your game.

Setting a Game Feature state during runtime

Game Features can be dynamically enabled and disabled during a runtime session.

BlueprintC++

As of Unreal Engine 5 Early Access 2, there are no native blueprint nodes that allow you to toggle on or off Game Features. Thankfully, Epic has exposed that functionality through console commands. Simply utilize the following two commands with the Execute Console Command blueprint node.

As of Unreal Engine 5.0.3, the console commands do not work in Shipped Builds.

Deactivate a game feature

DeactivateGameFeaturePlugin

Load & activate the game feature

Unload the game feature

Example

For this example, I have a Coin Collection Game Feature. When the green button is stepped on, the feature is toggled on. When the red button is stepped on, the feature is cleaned up and toggled off.

The Coin Collection Feature spawns collectible coins randomly and attaches a coin counter to the player's viewport.

Frequently Asked Questions

A list of frequently asked questions regarding this feature, and their answers.

When should I use this feature?

Module Game Features should be utilized when you need to update or create new features over the life of your project without the project specifically depending on them. You can also use them baseline for compartmentalizing both code and assets.

What are some usage examples?

With Game Features not being referenced by core gameplay, they can be utilized to control aspects of gameplay, memory management, and more on the fly.

For example, the Fortnite dev team utilizes Game Features for their vehicles. This allows them to enable or disable them for the different game modes easily.

Here are some other example use cases —

• Compartmentalizing code and/or assets
• Weapon Unlocks
• Ability Unlocks
• Level Instances
• Items
• NPCs
• FX
• Dialog
• Weather Effects
• Cutscenes

Just remember that feature-specific Game Features should be self-contained, and disabling them should not affect the core game.

My game feature isn't activating; why is that?

Make sure that you set your Game Feature state to Active when you want to enable it. Likewise, make sure to put it to Loaded or Registered to disable it.

If it still doesn't activate, check your logs. There is likely a warning or error that will help you pinpoint the issue.

Why is it recommended not to have the core game depend on a Game Feature?

When you take away something the engine is expecting to be there, it can cause a whole host of issues, such as —

• Game Crashes
• Errors
• Warnings
• General bugs

Links

Check out the following resources to learn more about the subject.

• Modular Game Features in UE5: plug n' play, the Unreal way
• Modular Game Features | Inside Unreal
• Valley of the Ancients Sample