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Unreal Engine 4 Terminology

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This page is dedicated to describing the commonly used terms when working with Unreal Engine 4. For example, if you find yourself asking questions like "What is an Actor", "What is a Component", or "What is a Pawn", this page will highlight and provide descriptions for those types of questions and more. Once you have an understanding of what each term means, links are provided for more documentation and guidance on working with them.

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Projects

A Project is a self-contained unit that holds all the content and code that make up an individual game and coincides with a set of directories on your disk. For example, in the image below the Hierarchy Tree of the Content Browser contains the same directory structure found inside your Project folder on your disk.

Click image for full view.

Although a Project is often referenced by the .uproject file associated with it, they are two separate files that exist alongside each other. The .uproject is a reference file used to create, open, or save a file, whereas the Project contains all of the files and folders associated with it.

You can create any number of different Projects which can all be maintained and developed in parallel. Both the Engine (and Editor) can easily switch between them which will allow you to work on multiple games at once or have several test projects in addition to your main game Project.

For more information, see: Unreal Game Projects

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Objects

The base building blocks in the Unreal Engine are called Objects and contain a lot of the essential "under the hood" functionality for your game assets. Just about everything in Unreal Engine 4 inherits (or gets some functionality) from an Object. In C++, UObject is the base class of all objects; it implements features such as garbage collections, metadata (UProperty) support for exposing variables to the Unreal Editor, and serialization for loading and saving.

For more information, see: Unreal Projects and Gameplay , Gameplay Programming

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Classes

A Class defines the behaviors and properties of a particular Actor or Object used in the creation of an Unreal Engine game. Classes are hierarchical, meaning a Class inherits information from its parent Classes (the Classes it was derived or "sub-classed" from) and passes that information to its children. Classes can be created in C++ code or in Blueprints.

For more information, see: Blueprint Class , Gameplay Classes , Class Creation Basics

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Actors

An Actor is any object that can be placed into a level. Actors are a generic Class that support 3D transformations such as translation, rotation, and scale. Actors can be created (spawned) and destroyed through gameplay code (C++ or Blueprints). In C++, AActor is the base class of all Actors.

There are several different types of Actors, some examples include: StaticMeshActor, CameraActor, and PlayerStartActor.

For more information, see: Actors and Geometry

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Components

A Component is a piece of functionality that can be added to an Actor. Components cannot exist by themselves, however when added to an Actor, the Actor will have access to and can use functionality provided by the Component.

For example, a Spot Light Component will allow your Actor to emit light like a spot light, a Rotating Movement Component will make your Actor spin around, or an Audio Component will make your Actor able to play sounds.

For more information, see: Components , Components Window , Components in Code

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Pawns

Pawns are a subclass of Actor and serve as an in-game avatar or persona, for example the characters in a game. Pawns can be controlled by a player or by the game's AI, in the form of non-player characters (NPCs).

When a Pawn is controlled by a human or AI player, it is considered as Possessed. Conversely, when a Pawn is not controlled by a human or AI player it is considered as Unpossessed.

For more information, see: Pawn , Possessing Pawns

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Characters

A Character is a subclass of a Pawn Actor that is intended to be used as a player character. The Character subclass includes a collision setup, input bindings for bipedal movement, and additional code for movement controlled by the player.

For more information, see: Character , Character Setup , How To - Character Movement

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PlayerController

The PlayerController Class is used to take player input and translate that into interactions in the game and every game has at least one PlayerController in it. A PlayerController often possesses a Pawn or Character as a representation of the player in a game.

The PlayerController is also the primary network interaction point for multiplayer games. During multiplayer play, the server has one instance of a PlayerController for every player in the game since it must be able to make network function calls to each player. Each client only has the PlayerController that corresponds to their player and can only use their PlayerController to communicate with the server.

For more information, see: PlayerController

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AIController

Just as the PlayerController possesses a Pawn as a representation of the player in a game, an AIController possesses a Pawn to represent a non-player character (NPC) in a game. By default, Pawns and Characters will end up with a base AIController unless they are specifically possessed by a PlayerController or told not to create an AIController for themselves.

For more information, see: AIController

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Brushes

A Brush is an Actor that describes a 3D volume that is placed in a level in order to define level geometry (referred to as BSPs) and gameplay volumes. Typically you will use BSP Brushes to prototype or block-out your levels for gameplay testing.

Volumes on the other hand have several uses depending upon the effects attached to them such as: Blocking Volumes (which are invisible and used to prevent Actors from passing through them), Pain Causing Volumes (which causes damage over time to any Actor that overlaps it) or Trigger Volumes (which are used as a way to cause events when an Actor enters or exits them).

For more information, see: Geometry Brush Actors , Geometry Editing Content Examples

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Levels

A Level is a user defined area of gameplay. Levels are created, viewed, and modified mainly by placing, transforming, and editing the properties of the Actors it contains. In the Unreal Editor, each Level is saved as a separate .umap file, which is also why you will sometimes see them referred to as Maps.

For more information, see: Levels , Level Editor , Level Design Content Examples

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World

A World contains a list of Levels that are loaded. It handles the streaming of Levels and the spawning (creation) of dynamic Actors.

Direct interaction with a World is not necessary, but it does help provide a specific reference point within the game structure (ie: mentioning World directly means you are not speaking about Levels, Maps or the game).

For more information, see: World Composition User Guide

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GameModes

The GameMode Class is responsible for setting the rules of the game that is being played. The rules can include how players join the game, whether or not a game can be paused, and level transitions, as well as any game-specific behavior such as win conditions.

You can set the default GameMode in the Project Settings, but can override it on a per-Level basis. Regardless of how you choose to implement the GameMode, there is always only one GameMode present per-level. In a multiplayer game, the GameMode only exists on the server and the rules are replicated (sent) to each of the connected clients.

For more information, see: GameMode , Setting Up a Game Mode in Blueprints

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GameStates

The GameState contains the information that you want replicated to every client in a game, or more simply it is 'The State of the Game' for everyone connected.

It often contains information about game score, whether a match has started or not, how many AI to spawn based upon the number of players in the world, and other game specific information.

For mutliplayer games, there is one instance of the GameState on each player's machine with the server's instance being the authoritative one (or the one that clients get their updated information from).

For more information, see: GameState

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PlayerStates

A PlayerState is the state of a participant in the game, such as a human player or a bot that is simulating a player. Non-player AI that exists as part of the game world would not have a PlayerState.

Example data that would be appropriate in a PlayerState include player name or score, their current level or health, or whether they are currently carrying the flag in a Capture the Flag game.

For multiplayer games, PlayerStates for all players exist on all machines (unlike PlayerControllers) and can replicate data from the server to the client to keep things in sync.

For more information, see: Gameplay Framework Quick Reference