The Unity Engine was initially released in 2005 for the purposes of democratizing the game development industry. Its goal was to provide professional but affordable game development tools aimed mainly at amateur game developers. Unity can create both 2D and 3D applications. The engine typically has a major version update every year with multiple smaller updates throughout the year. Unity is free for developers that bring in under $100,000 in revenue in a 12-month period. After that, there are 2 different pricing models. Though originally designed to build games, today Unity is used across multiple industries including automotive, architecture, engineering, construction, film, education, and retail.

Anatomy of a Unity Project Folder

When a new project is created, Unity creates several folders as a part of the project. Over the years and versions of Unity, this default folder structure has changed somewhat, but it now generally contains the following folders:

Assets

This is the folder where all game resources are stored, including scripts, textures, sound, and custom editor scripts. The organization of the folder can vary greatly from one project to another and from one organization to another. There can be numerous subfolders in the Assets folder, depending on how the project is organized. For example, there may be a folder for scenes, one for scripts, one for audio, or one for sprites. There is no limit to how deep the organization can be.

As a best practice, subfolders in the Assets folder should be created within Unity and not the computer's local file system. Likewise, assets should be added directly to the folders in the Unity Editor and not the file explorer as seen above. This is particularly important due to the way Unity constructs metadata for assets.

Unity reserves several special folder names under the asset folder. These folders are Editor, Editor Default Resources, Gizmos, Resources, Standard Assets, and Streaming Assets. Not every project will have all of these folders.

Assets/Editor — This folder is for custom editor scripts that extend the functionality of the Unity editor. These scripts will run in the editor but not in the project at runtime. Multiple Editor folders can exist in the Assets Folder. The execution of the editor scripts varies depending on where in the folder structure the editor file exists.

Assets/Editor Default Resources — This is where asset files used by Editor scripts are stored. There can only be one such folder and it must be placed in the Assets folder root. There can be subfolders in this folder.

Assets/Gizmos — Gizmos are graphics in the scene view which can help to visualize design details. This folder stores images used for gizmos. There can only be one folder and it must be placed in the Assets folder root. Gizmo examples are seen below with the red squares around them. The one on the left is the main camera’s position and rotation. The one on the right represents a light source. These two are Unity built in gizmos:

Assets/Resources — This folder stores resources so that they can be loaded on demand in a Unity project. There can be multiple resource folders. On demand loading is helpful for dynamically loading game objects that don’t have instances created by designers during design time. In other words, these resources may not have corresponding game objects placed in the scene at design time and can be loaded dynamically at run time.

Assets/Standard Assets — This folder stores any standard asset packages that have been imported into a project. There can be only one standard assets folder. Standard assets are free assets maintained by Unity.

Assets/Streaming Assets — This folder is for assets that will remain in their original format and later be streamed into the Unity application, instead of directly incorporating them into the project’s build. An example would be a video file from the filesystem. There can only be 1 streaming assets folder in the project.

Library

Moving on from the Assets folder, the next folder is Library. This is a local cache used by Unity for imported assets. It can be deleted and will be regenerated by unity automatically. All that is needed to recreate the folder are source assets and .meta files. If this folder is deleted, Unity will reimport all asset information and regenerate the folder the next time the project is opened in the editor. This folder should not be included in Version Control. These imported assets are used by Unity to save time when Unity is running.

Of special note in the Library folder is the package cache folder. This contains information about all the packages installed with the current project. Though this can be regenerated by Unity like the other items in the Library folder, for archival purposes, it is important that this file not be deleted. This is because it may be helpful to be able to see what packages are included in the project without having to regenerate the cache, which would require opening the project in its appropriate editor version.

Packages

This folder contains the manifest file in JSON format used to maintain the dependencies link between packages. The manifest file is used to regenerate the package cache in the library folder. It also contains a file listing the individual packages installed with the project. These are used by the Unity Package Manager. The package manager was added in Unity 2018.1. Prior versions of Unity will not contain the package manager and the packages folder will not exist in those cases.

Project Settings

This folder contains all project settings from the project settings menu. It also includes editor version number and build settings and a slew of other settings used by Unity systems. Editor version number, as a standalone file, was not added until Unity 5. For any version before that, the editor version number can be found in the project settings file.

Game engines are software development tools for creating interactive software. They package together libraries and software which simplify the development of interactive software. Game engines are a widely used tool in the creation of real-time 3D VR software, and many engines support VR production workflows out-of-the-box.

A modern game engine will typically include:

• A 3D or 2D renderer, which supports the rendering of a moving sequence in real-time.

• Physics simulation.

• Asset import and management.

• Scripting and programming tools to support dynamic, simulated and interactive elements.

• Sound processing.

• Extension through plugins and/or custom code.

There are numerous engines in use today. For real-time 3D rendering applications such as VR, Unity and Unreal Engine are currently the two most popular. Both are free to download and use non-commercially, which has contributed to their popularity.

An important implication of using an engine is that much programming has already happened before work on a project begins. The engines provides a toolset that can be used to realise the project and generate executable software, but as a creator you do not necessarily have full control or authorship of the code.

List of Engines

Resources

Adrian Courrèges (2020) Graphics Studies Compilation. URL: http://www.adriancourreges.com/blog/2020/12/29/graphics-studies-compilation/.

baldurk (n.d.). Graphics in Plain Language: An introduction to how modern graphics work in video games. URL: https://renderdoc.org/blog/Graphics-in-Plain-Language/Part-1.html.

Brown University VR Software Wiki. URL: https://sites.google.com/view/brown-vr-sw-review-2018/home

Godot Engine is a free open source 3D game engine for Android, Linux, Mac and Windows. A WebEditor is also available.

Some information with relevance to XR preservation, quote from the features list:

XR support

Godot makes cross-platform Augmented and Virtual Reality development easy.

• Works with many headsets including the Meta Quest, Valve Index, HTC Vive, Oculus Rift, all Microsoft MR headsets, and many more.

• Support for OpenXR, an emerging open standard that most hardware vendors are moving to.

• Plugins give access to various proprietary SDKs, such as OpenVR (SteamVR) and the legacy Oculus SDKs.

• WebXR can deliver AR/VR experiences via a web browser.

• ARKit allows creating AR apps for iOS.

Multi-platform editor

Create games on any desktop OS and Android.

• Works on Windows, macOS, Linux, *BSD and Android (experimental). The editor runs in 32-bit and 64-bit on all platforms, with native Apple Silicon support.

• Small download (around 35 MB), and you are ready to go.

• Easy to compile on any platform (no dependency hell).

Multi-platform deploy

Deploy games everywhere!

• Export to desktop platforms: Windows, macOS, Linux, UWP, and *BSD.

• Export to mobile platforms: iOS and Android.

• Consoles: Nintendo Switch, PlayStation 4, Xbox One via third-party providers (read more).

• Export to the web using HTML5 and WebAssembly.

• One-click deploy & export to most platforms. Easily create custom builds as well.

Unreal Engine 4 (UE4) is a real-time 3D engine developed by Epic Games. The first version of Unreal Engine was created during the development of the 1998 game Unreal, at which point Epic Game started licencing the engine to other developers. Version 4.0 was released in 2014, and has been followed by 27 subversions (the latest is 4.27). Unreal Engine 5, announced in 2020, is expected to supersede UE4 at some point in the near future. UE4 is not an open-source engine (see the EULA), but the engine source code is freely available via their GitHub repository.

Anatomy of a UE4 Project

A UE4 project consists of a collection of files and folders conforming to a well defined structure. A project folder typically contains the following at the top-level (more detail in the UE4 docs):

• Binaries: If the project has been compiled for a specific platform, this contains the files produced.

• Build: Contains files required to build the project for different platforms.

• Config: Contains project settings stored in plain text files with the .ini extension.

• Content: Contains the maps, assets (e.g. 3D models, materials, blueprints) and other custom content used by the project, including any third-party packages downloaded from the Unreal Marketplace.

• DerivedDataCache and Intermediate: Contain temporary files generated during the build process (e.g. shader compilation).

• Saved: Contains saved data created by the editor as it runs, including autosaves, crash reports and logs.

• A .uproject file: The project file with which the project can be launched. Actually a json file containing structured information describing the project, including the UE4 version, enabled plugins and target platforms.

Anatomy of a UE4 Build

A UE4 build consists of set of files and folders that allow the software to be run on a suitable host computer.

Some elements dependent on whether Development or Shipping option is selected prior to build, and other packaging options in UE4.

Preservation Considerations

Overview

• Has been updated an average of 4 times per year since first release in 2014. Updates can result in deprecation or removal of features, or incompatibility with plugins. Unreal Engine 5 was released in 2022, which may mean an end to UE4 updates.

• Free source code access via GitHub repository (note that the Unreal Engine EULA applies).

• Royalty payments only required with high product revenues, so unlikely to impact cultural heritage context.

• For custom C++ projects Visual Studio dependencies are difficult to manage from an archival perspective.

• Transforms imported assets to the poorly documented internal format (.uasset). More work is required to understand whether this transformation is lossless.

Access and Licencing

Export Formats

When an asset is imported to Unreal Engine 4 it is converted to the UE4 UASSET (.uasset) format. This format is not well documented, although there is some partial reverse engineering work here. A UASSET can be re-exported from the engine in a variety of formats depending on the asset type. To do so, you need to right click on the asset in the Content Browser, and navigate to Asset Actions -> Export.

The information below was derived from testing in Unreal Engine 4.27. Note that is simply a list of the export formats available and exports have not been tested against original import format.

3D Models (Static) Export Formats

Game Dependencies

Windows applications created using the UE4 editor have a set of dependencies similar to the editor. These are automatically packaged with an application when built from the editor, and are installed when the application is run by an installer program called UE4PrereqSetup_x64.exe. This can be located in the application directory: [UE4GameRootLocation]\Engine\Extras\Redist\en-us

Editor Dependencies

These dependencies are required to run the editor, or applications created using the editor.

Build Dependencies

These dependencies are required to build software from the editor for particular platforms.

UE4 Resources

• Epic Game, Unreal Engine 4.27 Glossary, URL: https://docs.unrealengine.com/4.27/en-US/Basics/Glossary/

• David Lightbown, 2018, Classic Tools Retrospective: Tim Sweeney on the first version of the Unreal Editor. URL: https://web.archive.org/web/20180823012812/https://www.gamasutra.com/blogs/DavidLightbown/20180109/309414/Classic_Tools_Retrospective_Tim_Sweeney_on_the_first_version_of_the_Unreal_Editor.php