Actors: Components, Content and Editors

This article extends on the basic primer by further explaining the concepts in the title and how to use some of the tools and best practices.

You are reading an old article for Unreal Engine 4 - it should still work for Unreal Engine 5 though!

Overview

Actors is what Unreal Engine generally classifies as any object that can be placed into a level and manipulated in 3D space, with a position, rotation and scale. Actors should be mainly thought of as empty containers that can hold one or many Components. Components then reference different types of Content, which can be created internally or externally, or come as part of a Component. Together, components build out an Actor.

For example, when considering a Lamp that will be placed in the level; a Lamp Actor will consist of a StaticMesh Component that will reference some externally imported geometry and will be assigned an internally created Material, and will also consist of a Light Component that consists of a light source.

This article will cover these concepts and the general different types of content in Unreal Engine.

Content Management

An important part of using a game engine is keeping files and the level editor tidy and easy to read. Common organisational techniques include:

Unreal Engine does not accept spaces in names. Use underscores (_) or camel-casing (thisIsAnExample) instead.
Name all objects following a convention based on the type of content that they are. For example, use the suffix SM for all static meshes (SM_Wall, SM_Door), or M for materials (M_Aluminium, M_TimberSlat)
Grouping like-objects together this means: organising like-Content into folders in the Content Browser and like-Actors into folders in the World Outliner. For example, a Static_Meshes folder to hold all geometry.

For a full list of conventions, refer to:

A new, community-hosted Unreal Engine WikiUnreal Engine Forums

Content

Content refers to all types of objects that can be found in the Content Browser. External Content is any content that has been created in an external application, like mesh geometry and rigs, and Internal Content can be Unreal-specific objects like Materials and Blueprints, as well as objects tied to components.

Externally Created

Static Meshes

Skeletal Meshes

Sounds

Skeletal Animations

Textures

Internally Created

Materials

Particle Systems

Cinematics

Blueprints

Blueprint Scripts

AI and Navigation

Physics

Lighting

Visual Effects

Volumes

Importing Content

Drag & Drop from your file explorer into the content browser, or alternatively use the [Import] button [1 below].

As aforementioned in 0.1 Content Management, use folders to organise your Content. Folders can be created using [RMB] or the green [Add New] button.

Moving Content Around

Content can be moved around the Content Browser by dragging objects around using the Sources Panel. The Sources Panel can be collapsed or expanded using the button indicated below in red.

Finding a Referenced Content in the Content Browser

When you need to quickly find where a piece of content is referenced by another piece of content, you can use the magnifying glass, which reveals that piece of content in the browser for you.

Actors & Components

Actors is what Unreal Engine generally classifies as any object that exists in a level and containers that can hold one or many Components.

Creating Actors

Actors refer only to when they exist in the Level, in other words, if it makes it to the level editor.

Empty/New Actors

Ensure that you are in using [Place] mode of the Level Editor. This is the default mode as the leftmost toggle in the Modes panel.
Using the Basic tab, empty, or primitive Static Meshes Actors can be inserted into the scene.

From Content

Simply drag and drop Content from the Content Browser into the Viewport and it will convert it into the relevant Actor for you if possible. For example, dragging in a mesh for a chair will create an Actor with Component Static Mesh attached to it, referencing your mesh.

Component Structure

To view an Actor's Component hierarchy, refer to the Actor's Details panel.

Reference

Aspect

Description

Actor and Components Details

This section of the Details panel describes the selected Actor's hierarchy of components.

Add Component

Opens up a search panel for adding Components

Component Root

The Component of the highest hierarchy (leftmost indentation) is the reference for the objects transform axis for moving and scaling. If an empty Actor is created, this defaults to a DefaultSceneRoot Component.

Components

Hierarchies

This sub-panel's contents can be manipulated as you would the World Outliner, [drag and drop]Components to that you which you want it to fall under.

Replacing the Root and DefaultSceneRoot

The Component Root can be replaced by dragging the desired new Root Component over the existing Root. This is how you can replace the DefaultSceneRoot of empty Actors as well.

Components Types

Components are the modular attachments to an Actor that may references Content in some way. Here are the most commonly used Components and the Content that they accept if any.

Component

External Content

Usage

Static Mesh

Geometry, Textures and materials

Adds to the Actor a reference to a piece of geometry that consists of static polygons. These can be layered with materials to affect their surface appearance.

Paper 2D

Sprite Textures

Adds to the Actor the utility to render and display 2D objects, it is a type of flat mesh.

Audio

Sound files, Music

Adds to the Actor the ability to play a sound.

Skeletal Mesh

Skeletal Meshes

Adds to the Actor a reference to Content that is structured meshes with a internal skeleton that is usually used with animations

Physics

n/a

Physics Components are a type of components that allows the actor to utilise the Physics Engine. Destructible for destruction effects, Constraints for connecting meshes together, Handle makes objects 'grab-able' and Forces for forces.

Camera

n/a

Adds a camera to the actor, usually used to add a camera to the to simulate the player's point of view.

Light

n/a

Adds light sources to the actor.

Working with Actors

Mobility

Mobility is a concept that applies to all content in the level and is relevant for two kinds of objects: lighting and everything else. It relates to the limits of how an object interacts with the scene during play; can it be moved, can its parameters be updated, how does it contribute to the lighting of the level. While the type of mobility needed is dependent on the function you require, do note that this is tied to the performance of the experience, as more dynamic actors mean more computational power.

State

Geometry

Light

Static

Does not update or move in anyway and will not be interacted with. Static Geometry will have their textures baked with lighting when building.

Least resource intensive.

For Lights, this means that it will contribute to the baking of lighting.

Least resource intensive.

Stationary

Cannot move, but can update during play, such as its properties. Lighting is not baked for these objects.

Stationary Lights will contribute to baked lighting. During play, can be updated, e.g their colour and range, but will only contribute to direct lighting.

Movable

Can move, update, and be added/removed during play. Shadows and lighting are calculated in real time.

These lights will only cast dynamic shadows during play, and will not contribute to baked lighting.

For some further details regarding lighting, refer to:

Lighting & Mobility

Manipulating Actors in the Level Editor

Actors are visible in scene upon creation, and can be found in the World Outliner.

Transforming Actors

The viewport toolbar in the top right features a host of transformation controls. When a object is selected, this changes the selection widget to a tool.

Tool

Shortcut

Move

Rotate

Scale

Using the Details Panel

An actor can also be manipulated through their details panel, along with their transform, all their other parameters are listed as well.

Actor and Component Details

When a Component is added to the Actor, this will also add to the Details panel of that Actor. For example, the image belows shows the common Static Mesh and Material parameters that get added by the StaticMesh Component.

By default, Actors will have access to common parameters, here are the main ones:

Physics and Collisions for turning Physics on/off and how it behaves when collided with.
Lighting parameters for how it deals with lightmaps (Lightmass System) and shadow casting.
Rendering for whether it appears in the game or not.
Tags for referencing in Scripting.
Actor settings for AI and gameplay.

Actor Visibility

As mentioned previously, Actors can be hidden via the World Outliner but this only applies to the Level Editor and they will still be visible and a part of the experience. To truly hide an Actor and all of its interactions, use the [Visible] toggle in the Actor's Details panel under Rendering.

Editor Modes

These modes in the Modes panel give access to additional tools, editors, interfaces that deal with content and actors

[Place] mode is the only editing mode that allows you to interact with all of the Actors in your scene, content browser and other editors. If you find that you are unable to edit an Actor or move something around, ensure that you are back in [Place] mode.

Tool

Description

Shortcut

Activates Place mode for placing and manipulating Actors in your scene.

Place allows for the creation of actors. Some of these actors contribute to the environment, like Lights and Visual Effects, while Basics and Volumes provides for interactivity. For an deeper look into some of the elements, refer to the section below on Content Types.

Shift + 1

Toggles Paint mode for painting vertex colors and textures on Static Mesh Actors directly in the viewport.

Allows you to paint on meshes.

Shift + 2

Toggles Landscape mode for creating Landscape terrains.

Allows for the creation of basic landscapes.

Shift + 3

Toggles Foliage mode for painting instanced foliage.

The foliage mode lets you 'paint' by distributing meshes along a surface, while this tool is named foliage, this tool will distribute any mesh geometry that you give it.

Shift + 4

Toggles Geometry Editing mode for modifying Brushes to geometry.

Provides basic geometry tools for unexpected mesh editing like flipping mesh faces, triangulation, mesh welding and optimisation. These processes should be carried out in your geometry-making program of choice.

Shift + 5

Controls

General controls for using any of the editors other than [Place] mode as they all use a brush tool

Control

Function

LMB

Paint

Shift+LMB

Erase

Content Types & Editors

Accessing Editors

Many content, whether external or internal, has a unique editor associated with them. These are usually accessed through the content browser by double-clicking on the content file.

Levels

Your project experience can be thought of as a collection of, or a single level. Levels themselves are collections of geometry, effects, lighting, interactive elements that work together to create the experience.

In Unreal Engine, levels are expressed as objects that are files that can be saved, operated on and opened like any other.

Static Meshes

Static Meshes refers to objects without a rig or pre-animated qualities. World geometry such as buildings components and future fit into this category.

Naming Convention: SM_(Object Name)

Best Practice:

Geometry must be a triangular mesh
Must be of the .fbx file type.
Keep it as simplified as possible
Upon creation in your preferred modelling software, ensure the origin of the geometry is appropriate, as this makes up the objects point of reference when transforming
Should be be prepared with UV unwrapping for both textures and lightmaps for most accurate representation of materiality.

Editor: Static Mesh Editor

[Access, what you can do here]

Materials & Textures

Materials are what you apply to surfaces to define what they look like and how they interact with light. They are formed by various properties that are given data through textures: images of various properties, numbers/data and mathematical calculations. These are layered in Unreal Engine's material editor.

Naming Convention:

Materials: M_(Material Type)
Textures: T_(Image Content)_(Material Input Type)

Best Practice:

Textures are accepted in wide range of image formats.
Use high quality textures where possible
Ensure UVs of the applicant object is suitable for the material.

Editor: Material Editor and Texture Editor

[Access, what you can do here]

For a more in-depth look into how Materials work and are created, refer to:

Materials & Textures

Lights

Lights are created internally through Components, there are different types of light for how they project light: point lights, spotlights, directional lights, rectangular lights and skylights.

For more information on lights, but mainly the concept of lighting, refer to:

Lighting & Mobility

Blueprints and Blueprint Scripting

Blueprints function like externalised Actors that you can access through the Content Browser. They are a product of the concept of 'prefabrications' that are completed hierarchies of components (like Actors,) as a way to manage modular content.

Naming Convention: BP_(Blueprint Description)

Blueprint Scripts refers to the Visual Scripting system found within Blueprints that allows interactivity to be programmed, usually referring to components in its Blueprint.

Editor: Blueprint Editor

For a more in-depth guide to both concepts as they are intrinsically linked, refer to:

Interactivity & Blueprints

Cameras

Cameras are the target for the Engine's rendering engine.

Player Camera

The player character will always have a camera attached. For more information on Player Cameras, refer to:

Player: VR and non-VR

Cinematic Cameras

Cinematic Cameras are Camera Actors based on real physical cameras to simulate traditional rendering cameras. This object created through Place mode. For more information, refer to:

Outputting Content

Visual Effects

Unreal Engine comes with a host of visual effects packaged as Actors. These objects are created through Place mode.

Post Process Volume

Post Process Volume is a volume, so an area of 3D space, that applys post-process image grading control, like hue and contrast to any cameras and player inside.

Fog

Fog adds atmospheric experience, it is available in two types:

Atmospheric Fog is a linear fog
Exponential Height Fog is [adjustable in such and such ways]

Sphere & Box Reflection Capture

Used to boost reflections for reflective materials. These actors act like a two-way mirrors for reflective materials near it. It captures a projection of what should be reflected in the material and projects it back to simulate reflections.

Volumes

Volumes are 3D spaces that have built-in functionality. The Post Process Volume is an example of this, other volumes include Sound Volumes and Nav Mesh Bounds Volumes that limits sound and navigable areas respectively. These are object created through Place mode.

Pawns & Characters

Pawns are Actor or Blueprint representations of players and other AI controlled ements in the experience. These are usually classified by their type.

Naming Convention:

Characters: CH_(Character)

Triggers

Triggers are Actors that can track when an element has been interacted with through Collisions, to allow for the sequencing or response of events.These objects are created through Place mode.

Triggers come in forms relevant to their type: Box, Sphere and Capsule.

For more information on how these are used:

Interactivity & Blueprints

Particle Systems

Unreal Engine has a Editor for particle systems called Cascade. Particle systems are used to create visual effects like fire, sparks and smoke. Particle systems are created through the Content Browser.

Naming Convention: PS_(Particle Effect)