Draft:Unreal Engine
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Original author(s) | Tim Sweeney |
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Developer(s) | Epic Games |
Stable release | 5.4
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Written in | C++ |
Operating system | Windows, Linux, macOS |
License | Source-available commercial software with royalty model for commercial use[1] |
Website | www |
Unreal Engine (UE) is a series of 3D computer graphics and game engines developed by Epic Games, first showcased in the 1998 first-person shooter video game Unreal. Initially developed for PC first-person shooters, it has since been used in a variety of genres of games and has been adopted by other industries, most notably the film and television industry. Unreal Engine is written in C++ and features a high degree of portability, supporting a wide range of desktop, mobile, console, and virtual reality platforms.
The latest generation, Unreal Engine 5, was launched in April 2022. Its source code is available on GitHub, and commercial use is granted based on a royalty model, with Epic charging 5% of revenues over US $1 million, which is waived for games published on the Epic Games Store. Epic has incorporated features in the engine from acquired companies such as Quixel, which is seen as helped by Fortnite's revenue.
In 2014, Unreal Engine was named the world's "most successful videogame engine" by Guinness World Records.[2]
History
[edit]First generation
[edit]Unreal Engine 1 was initially developed in 1995 by Epic Games founder Tim Sweeney for Unreal. Epic later began to license the Engine to other game studios.
Unreal Engine 2
[edit]Unreal Engine 2 transitioned the engine from software rendering to hardware rendering and brought support for multiple platforms like the PS2. The first game using UE2 was released in 2002 and its last update was shipped in 2005.
Unreal Engine 3
[edit]Unreal Engine 3 was one of the first game engines to support multithreading. It used DirectX 9 as its baseline graphics API, simplifying its rendering code. The first games using UE3 were released at the end of 2006.
Unreal Engine 4
[edit]Unreal Engine 4 brought support for physically based materials and the "Blueprints" visual scripting system . The first game using UE4 was released in April 2014.
Unreal Engine 5
[edit]Unreal Engine 5 was revealed in May 2020 and officially released in April 2022. Major features of Unreal Engine 5 include Nanite, a virtualized geometry system that allows game developers to use arbitrarily high quality meshes with automatically generated Level of Detail, and Lumen, a dynamic global illumination and reflections system that uses software and hardware ray tracing.
Scripting
[edit]UnrealScript
[edit]Paradigm | Object-oriented, generic |
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Developer | Tim Sweeney |
First appeared | May 1998 |
Typing discipline | Static, strong, safe |
OS | Cross-platform (multi-platform) |
Filename extensions | .uc .uci .upkg |
Website | docs.unrealengine.com |
Influenced by | |
C++, Java |
UnrealScript (often abbreviated to UScript) was Unreal Engine's native scripting language used for authoring game code and gameplay events before the release of Unreal Engine 4. The language was designed for simple, high-level game programming.[3] UnrealScript was programmed by Tim Sweeney,[4] who also created an earlier game scripting language, ZZT-OOP.[5] Deus Ex lead programmer Chris Norden described it as "super flexible" but noted its low execution speed.[6]
Similar to Java, UnrealScript was object-oriented without multiple inheritance (classes all inherit from a common Object class), and classes were defined in individual files named for the class they define. Unlike Java, UnrealScript did not have object wrappers for primitive types. Interfaces were only supported in Unreal Engine generation 3 and a few Unreal Engine 2 games. UnrealScript supported operator overloading, but not method overloading, except for optional parameters.
At the 2012 Game Developers Conference, Epic announced that UnrealScript was being removed from Unreal Engine 4 in favor of C++.[7] Visual scripting would be supported by the Blueprints Visual Scripting system, a replacement for the earlier Kismet visual scripting system.[8][9]
One of the key moments in Unreal Engine 4's development was, we had a series of debates about UnrealScript – the scripting language I'd built that we'd carried through three generations. And what we needed to do to make it competitive in the future. And we kept going through bigger and bigger feature lists of what we needed to do to upgrade it, and who could possibly do the work, and it was getting really, really unwieldy. And there was this massive meeting to try and sort it out, and try to cut things and decide what to keep, and plan and...there was this point where I looked at that and said 'you know, everything you're proposing to add to UnrealScript is already in C++. Why don't we just kill UnrealScript and move to pure C++? You know, maximum performance and maximum debuggability. It gives us all these advantages.'
Verse
[edit]Verse is the new scripting language for Unreal Engine, first implemented in Fortnite.[11] Simon Peyton Jones, known for his contributions to the Haskell programming language, joined Epic Games in December 2021 as Engineering Fellow to work on Verse with his long-time colleague Lennart Augustsson and others.[12] Conceived by Sweeney,[13] it was officially presented at Haskell eXchange in December 2022 as an open source functional-logic language for the metaverse.[14] A research paper, titled The Verse Calculus: a Core Calculus for Functional Logic Programming, was also published.[15]
The language was eventually launched in March 2023 as part of the release of the Unreal Editor for Fortnite (UEFN) at the Game Developers Conference, with plans to be available to all Unreal Engine users by 2025.[11]
Marketplace
[edit]With Unreal Engine 4, Epic opened the Unreal Engine Marketplace in September 2014. The Marketplace is a digital storefront that allows content creators and developers to provide art assets, models, sounds, environments, code snippets, and other features that others could purchase, along with tutorials and other guides. Some content is provided for free by Epic, including previously offered Unreal assets and tutorials.[16] Prior to July 2018, Epic took a 30% share of the sales but due to the success of Unreal and Fortnite Battle Royale, Epic retroactively reduced its take to 12%.[17]
Usage
[edit]Video games
[edit]Unreal Engine was originally designed to be used as the underlying technology for video games. The engine is used in a number of high-profile game titles with high graphics capabilities, including Hogwarts Legacy,[18] PUBG: Battlegrounds, Final Fantasy VII Remake, Valorant and Yoshi's Crafted World, in addition to games developed by Epic, including Gears of War and Fortnite.[19][20][21] Polish game developer CD Projekt is also planning to use the engine after retiring their in-house REDengine; their first game to use Unreal will be a remake of The Witcher.[22][23][24][25]
Film and television
[edit]Unreal Engine has found use in film making to create virtual sets that can track with a camera's motion around actors and objects and be rendered in real time to large LED screens and atmospheric lighting systems. This allows for real-time composition of shots, immediate editing of the virtual sets as needed, and the ability to shoot multiple scenes within a short period by just changing the virtual world behind the actors. The overall appearance was recognized to appear more natural than typical chromakey effects.
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Among the productions to use these technologies were the live action television series The Mandalorian and Westworld and the animated series Zafari and Super Giant Robot Brothers. Jon Favreau and Lucasfilm's Industrial Light & Magic division worked with Epic in developing their StageCraft technology for The Mandalorian, based on a similar approach Favreau had used in The Lion King.[26][27][28][29][30] Favreau then shared this technology approach with Jonathan Nolan and Lisa Joy, the producers for Westworld. The show had already looked at the use of virtual sets before and had some technology established, but integrated the use of Unreal Engine as with StageCraft for its third season.[31][32]
Orca Studios, a Spanish-based company, has been working with Epic to establish multiple studios for virtual filming similar to the StageCraft approach with Unreal Engine providing the virtual sets, particularly during the COVID-19 pandemic, which restricted travel.[33]
In January 2021, Deadline Hollywood announced that Epic was using part of its Epic MegaGrants to back for the first time an animated feature film, Gilgamesh, to be produced fully in Unreal Engine by animation studios Hook Up, DuermeVela and FilmSharks.[34] As part of an extension of its MegaGrants, Epic also funded 45 additional projects since around 2020 for making movies and short films in the Unreal Engine.[35] By October 2022, Epic was working with several different groups at over 300 virtual sets across the world.[36]
Other uses
[edit]Unreal Engine has also been used by non-creative fields due to its availability and feature sets. It has been used as a basis for a virtual reality tool to explore pharmaceutical drug molecules in collaboration with other researchers, as a virtual environment to explore and design new buildings and automobiles, and used for cable news networks to support real-time graphics.[37]
![](http://upload.wikimedia.org/wikipedia/commons/thumb/4/46/Unreal_Government_Network_logo.png/250px-Unreal_Government_Network_logo.png)
In March 2012, Epic Games announced a partnership with Virtual Heroes of Applied Research Associates to launch Unreal Government Network, a program that handles Unreal Engine licenses for government agencies.[38] Several projects originated with this support agreement, including an anaesthesiology training software for U.S. Army physicians, a multiplayer crime scene simulation developed by the FBI Academy, and various applications for the Intelligence Advanced Research Projects Activity with the aim to help intelligence analysts recognize and mitigate cognitive biases that might affect their work.[39][40] Similarly, the DHS Science and Technology Directorate and the U.S. Army's Training and Doctrine Command and Research Laboratory employed the engine to develop a platform to train first responders titled Enhanced Dynamic Geo-Social Environment (EDGE).[41]
Awards
[edit]The engine has received numerous awards:
- Technology & Engineering Emmy Award from the National Academy of Television Arts and Sciences (NATAS) for "3D Engine Software for the Production of Animation" in 2018[42]
- Primetime Engineering Emmy Award from the Television Academy for exceptional developments in broadcast technology in 2020[43]
- Annie Award from ASIFA-Hollywood for technical advancement in animation in 2021[44]
- Game Developer Magazine Front Line Award for Best Game Engine for 2004,[45] 2005,[46] 2006,[47] 2007,[48] 2009,[49] 2010,[50] 2011,[51] and 2012[52]
- Develop Industry Excellence Award for Best Engine for 2009,[53] 2010,[54] 2011,[55] 2013,[56] 2016,[57] 2017,[58] and 2018[59]
- Guinness World Record for most successful video game engine[2]
Legal aspects
[edit]The state of the Unreal Engine came up in Epic's 2020 legal action against Apple Inc. claiming anticompetitive behavior in Apple's iOS App Store. Epic had uploaded a version of Fortnite that violated Apple's App Store allowances. Apple, in response, removed the Fortnite app and later threatened to terminate Epic's developer accounts which would have prevented Epic from updating the Unreal Engine for iOS and macOS.[60] The court agreed to grant Epic a permanent injunction against Apple to prevent Apple from taking this step, since the court agreed that would impact numerous third-party developers that rely on the Unreal Engine.[61]
See also
[edit]- Procedural generation
- Make Something Unreal
- Epic Citadel
- The Matrix Awakens
- On-set virtual production
References
[edit]- ^ "Unreal Engine End User License Agreement". Unreal Engine. Archived from the original on August 26, 2018. Retrieved August 26, 2018.
- ^ a b "Most successful videogame engine". Guinness World Records. July 16, 2014. Archived from the original on December 22, 2015.
- ^ "UDK - Design Goals of UnrealScript". Unreal Engine Docs. Archived from the original on July 3, 2013. Retrieved June 26, 2013.
- ^ Busby, Jason; Parrish, Zak; Wilson, Jeff (July 21, 2009). Introduction to Unreal Technology. InformIT. Archived from the original on September 30, 2012. Retrieved February 22, 2022.
- ^ Thomsen, Mike (February 23, 2010). "History of the Unreal Engine". IGN. Archived from the original on July 12, 2017. Retrieved August 13, 2017.
- ^ Lightbown, David (October 23, 2018). "Classic Tools Retrospective: The tools that built Deus Ex, with Chris Norden". Game Developer. Archived from the original on June 29, 2019. Retrieved February 22, 2022.
- ^ Schultz, Warren. "Unreal Engine 4 - First Look". About.com. Archived from the original on May 24, 2012. Retrieved December 29, 2017.
- ^ Nutt, Christian (March 21, 2014). "Epic's Tim Sweeney lays out the case for Unreal Engine 4". Game Developer. Archived from the original on October 3, 2017. Retrieved February 22, 2022.
- ^ Grayson, Nathan (July 20, 2012). "Fortnite's Jessen Talks Minecraft, PC Gaming, UE4". Rock, Paper, Shotgun. Archived from the original on May 1, 2018. Retrieved May 1, 2018.
- ^ Wawro, Alex (March 1, 2017). "For Tim Sweeney, advancing Epic means racing into AR and VR". Game Developer. Archived from the original on July 20, 2017. Retrieved February 22, 2022.
- ^ a b "Dive into Epic's announcements from GDC 2023". Unreal Engine. March 23, 2023. Archived from the original on March 23, 2023. Retrieved March 23, 2023.
- ^ Peyton Jones, Simon (November 5, 2021). "An Epic future for SPJ". Haskell Community Discourse. Archived from the original on May 20, 2022. Retrieved May 4, 2022.
- ^ "Interview with Simon Peyton Jones". Haskell Foundation. March 25, 2022. Archived from the original on March 27, 2023. Retrieved March 27, 2023.
So Tim Sweeney is the founder and CEO of Epic and he is a computer scientist and has been interested in programming for a long time. So he knows about Haskell and loves Haskell actually. So I think that's why he thought of people like me and Lennart and was keen to have us. But Verse isn't a Haskell clone by any means. It's a language that Tim has been designing sort of in his head actually for – I don't really quite know how long, I should ask him – around a decade. So it's informed by functional programming and imperative programming and game programming and logic programming. There's a lot going on in Verse. Lennart's and my job is to sort of reverse engineer Verse out of tim's head and get it set down in a kind of formal semantics that everybody else can make make sense of.
- ^ "Beyond Functional Programming: The Verse Programming Language (Simon Peyton Jones)". YouTube. December 12, 2022. Archived from the original on December 12, 2022. Retrieved December 12, 2022.
- ^ Augustsson, Lennart; Breitner, Joachim; Claessen, Koen; Jhala, Ranjit; Peyton Jones, Simon; Shivers, Olin; Steele, Guy; Sweeney, Tim (March 2023). "The Verse Calculus: a Core Calculus for Functional Logic Programming" (PDF). Simon.PeytonJones.org. Archived (PDF) from the original on March 15, 2023. Retrieved March 27, 2023.
- ^ Brown, Fraser (September 4, 2014). "The Unreal Engine Marketplace is open for business". PCGamesN. Archived from the original on July 13, 2018. Retrieved July 12, 2018.
- ^ Chalk, Andy (July 12, 2018). "Fortnite is making so much money that Epic is giving Unreal Marketplace creators a big raise". PC Gamer. Archived from the original on July 13, 2018. Retrieved July 12, 2018.
- ^ Vergara, Nico (February 2, 2023). "Is Hogwarts Legacy on Unreal Engine 5?". VideoGamer. Archived from the original on February 2, 2023. Retrieved February 27, 2023.
- ^ Bradshaw, Tim; Kruppa, Miles (August 12, 2020). "Epic and Unity rev their engines for the next era of entertainment". Financial Times. Archived from the original on August 12, 2020.
- ^ Bradshaw, Tim; Kruppa, Miles (August 13, 2020). "Epic and Unity rev their engines for the next era of entertainment". Ars Technica. Archived from the original on December 5, 2021.
- ^ Dealessandri, Marie (January 16, 2020). "What is the best game engine: is Unreal Engine right for you?". GamesIndustry.biz. Archived from the original on November 17, 2021. Retrieved July 19, 2021.
- ^ "The Witcher - A New Saga Begins". March 21, 2022. Archived from the original on April 12, 2022. Retrieved April 7, 2022.
- ^ "CD Projekt will swap REDengine for Unreal Engine 5 to create the next Witcher saga". Game Developer. March 22, 2022. Archived from the original on April 5, 2023. Retrieved April 6, 2023.
- ^ Patel, Ashkay (September 9, 2022). "After Cyberpunk 2077's Disastrous Launch, CDPR Is Ditching REDengine For Unreal". The Gamer. Archived from the original on January 19, 2023. Retrieved April 6, 2023.
- ^ Nightingale, Ed (October 26, 2022). "CD Projekt Red announces remake of first Witcher game". Eurogamer. Archived from the original on May 21, 2023. Retrieved August 26, 2022.
- ^ Lodderhose, Diana (May 21, 2023). "Technologies Like AI & Unreal Engine Are A Having Big Impact On The Entertainment Business, But Where Will It Go From Here?". Deadline.com. Archived from the original on July 31, 2023. Retrieved July 31, 2023.
- ^ "Upcoming Animated Series 'Zafari' Is Being Rendered Completely With The Unreal Game Engine". Cartoon Brew. September 12, 2017. Archived from the original on February 14, 2018. Retrieved July 31, 2023.
- ^ Grubb, Jeff (November 19, 2019). "Why 'The Mandalorian' cites Fortnite dev Epic Games in its credits". Venture Beat. Archived from the original on January 5, 2022. Retrieved August 1, 2020.
- ^ Desowitz, Bill (February 20, 2020). "'The Mandalorian': How ILM's Innovative StageCraft Tech Created a 'Star Wars' Virtual Universe". Yahoo News. Archived from the original on January 5, 2022. Retrieved August 1, 2020.
- ^ Good, Owen (February 20, 2020). "How Lucasfilm used Unreal Engine to make The Mandalorian". Polygon. Archived from the original on November 13, 2020. Retrieved August 1, 2020.
- ^ Vary, Adam (March 12, 2020). "'Westworld' Showrunners on the Series' Bold New Direction for Season 3". Variety. Archived from the original on March 9, 2022. Retrieved August 1, 2020.
- ^ Failes, Ian (June 25, 2020). "'Westworld's' journey into the LED screen revolution". Befores & Afters. Archived from the original on January 5, 2022. Retrieved November 17, 2020.
- ^ Hopewell, John (June 3, 2020). "'Mandalorian'-Style Virtual Technology Sound Stage Orca Studios Opens in Spain". Variety. Archived from the original on May 7, 2021. Retrieved August 1, 2020.
- ^ Wiseman, Andreas (January 21, 2021). "'Fortnite' Creator Epic Games Makes Foray Into Movies With Animated Pic 'Gilgamesh'". Deadline Hollywood. Archived from the original on January 21, 2021. Retrieved January 21, 2021.
- ^ Takahashi, Dean (April 26, 2021). "Spire Animation Studios kicks off Epic Games' new Unreal Shorts animated film program". Venture Beat. Archived from the original on October 6, 2021. Retrieved April 26, 2021.
- ^ Giardina, Carolyn (October 22, 2022). "Too Much Volume? The Tech Behind 'Mandalorian' and 'House of the Dragon' Faces Growing Pains". The Hollywood Reporter. Archived from the original on February 4, 2023. Retrieved February 5, 2023.
- ^ Yee, Erica (December 14, 2018). "The real reason Epic landed a $15 billion valuation is not Fortnite's viral video game success". CNBC. Archived from the original on November 9, 2021. Retrieved July 19, 2021.
- ^ Robertson, Adi (March 28, 2012). "Epic licensing Unreal Engine 3 for FBI training sim and other 'serious games'". The Verge. Archived from the original on November 15, 2022. Retrieved November 15, 2022.
- ^ "Unreal games engine licensed to FBI and other US agencies". BBC. March 28, 2012. Archived from the original on July 4, 2017. Retrieved July 18, 2017.
- ^ Brightman, James (March 27, 2012). "Epic Games launches Unreal Government Network for serious games applications". GamesIndustry.biz. Archived from the original on August 22, 2016. Retrieved June 24, 2017.
- ^ Barrie, Allison (November 21, 2013). "Army, DHS join forces for virtual training tech for first responders". Fox News. Archived from the original on November 16, 2015. Retrieved June 29, 2017.
- ^ Cowley, Dana (November 15, 2018). "Unreal Engine Wins Technology & Engineering Emmy® for Animation Production". Unreal Engine. Archived from the original on November 17, 2018. Retrieved November 16, 2018.
- ^ "Engineering Emmy Winners Announced". Emmys.com. October 8, 2020. Archived from the original on February 4, 2022. Retrieved October 10, 2020.
- ^ Davenport, Chris (March 4, 2021). "Epic Games' Unreal Engine Will be Recognized at Annie Awards". Gamerant. Archived from the original on April 27, 2021. Retrieved March 7, 2021.
- ^ "Front Line Awards 2004". Game Developer Magazine. January 2005. p. 14.
- ^ "Front Line Awards 2005". Game Developer Magazine. January 2006. p. 17.
- ^ "Front Line Awards 2006". Game Developer Magazine. January 2007. p. 14.
- ^ "Front Line Awards 2007". Game Developer Magazine. January 2008. p. 24.
- ^ "Front Line Awards 2009". Game Developer Magazine. January 2010. p. 11.
- ^ "Front Line Awards 2010". Game Developer Magazine. January 2011. p. 19.
- ^ "Front Line Awards 2011". Game Developer Magazine. January 2012. p. 10.
- ^ "Front Line Awards 2012". Game Developer Magazine. January 2013. p. 13.
- ^ French, Michael (July 16, 2009). "Develop Awards: The Winners In Full". Develop. Archived from the original on July 22, 2016. Retrieved July 15, 2016.
- ^ Crossley, Rob (July 15, 2010). "Develop Awards: Unreal Engine wins tight race". MCV. Develop. Archived from the original on July 22, 2016. Retrieved July 15, 2016.
- ^ Hoggins, Tom (July 21, 2011). "Develop Industry Excellence Award winners announced". The Daily Telegraph. Archived from the original on July 22, 2016. Retrieved July 15, 2016.
- ^ French, Michael (July 10, 2013). "Game development stars honoured in Brighton". Develop. Archived from the original on July 22, 2016. Retrieved July 15, 2016.
- ^ Kayser, Daniel (July 14, 2016). "Unreal Engine 4 Wins Develop Industry Excellence Award for Best Engine". Unreal Engine. Epic Games. Archived from the original on July 22, 2016. Retrieved July 15, 2016.
- ^ Cowley, Dana (July 25, 2017). "Develop Industry Excellence Awards 2017: Best Engine". Unreal Engine. Archived from the original on August 5, 2017. Retrieved July 26, 2017.
- ^ Barton, Seth (July 12, 2018). "The Develop Awards 2018: All the winners!". MCV. Archived from the original on February 13, 2021. Retrieved July 18, 2018.
- ^ Bell, Elliot (August 14, 2020). "Daily Crunch: Apple removes Fortnite from the App Store". Archived from the original on June 5, 2021. Retrieved August 14, 2020.
- ^ Statt, Nick; Peters, Jay (October 9, 2020). "Epic judge permanently restrains Apple from blocking Unreal Engine, but won't force Fortnite". The Verge. Archived from the original on February 4, 2022. Retrieved October 9, 2020.
Further reading
[edit]- Kosak, Dave. "Talking with Tim Sweeney about the evolution of a game engine". GameSpy. Archived from the original on June 21, 2001. Retrieved June 21, 2001.
- Buecheler, Christopher. "Tim Sweeney discusses the Unreal Engine". GameSpy. Archived from the original on June 21, 2001. Retrieved June 21, 2001.
- Keighley, Geoffrey. "Blinded By Reality: The True Story Behind the Creation of Unreal". GameSpot. Archived from the original on May 19, 2001.
- Herz, J.C (December 2, 1999). "GAME THEORY; For Game Maker, There's Gold in the Code". The New York Times. Archived from the original on September 19, 2017. Retrieved December 20, 2017.
- Thomsen, Mike (February 2010). "History of the Unreal Engine". IGN. Archived from the original on July 12, 2017. Retrieved February 3, 2015.
- Bullis, Kevin (November 2011). "Epic Games Finds New Customers". MIT Technology Review. Archived from the original on May 2, 2019. Retrieved August 12, 2017.
- Horvath, Stu (May 2012). "The Imagination Engine: Why Next-Gen Videogames Will Rock Your World". Wired.
- Totilo, Stephen (June 2012). "How Unreal Engine 4 Will Change The Next Games You Play". Kotaku. Archived from the original on December 21, 2017. Retrieved December 19, 2017.
- Steiner, Brian (June 2013). "How The Unreal Engine Became A Real Gaming Powerhouse". Popular Mechanics. Archived from the original on April 27, 2021. Retrieved February 6, 2015.
- Harrington, Richard (November 2016). "The game is on: automotive product development in a new virtual world". Automotive World. Archived from the original on August 16, 2017. Retrieved August 16, 2017.
- Gaudiosi, John (March 2017). "Epic Games' Unreal Engine Is Opening Enterprise Business Doors In Automotive, And Other Industries". [a]listdaily. Archived from the original on June 23, 2022. Retrieved August 16, 2017.
- Batchelor, James (April 2017). "Sweeney: 'The future of the games industry? Make everyone a creator'". GamesIndustry.biz. Archived from the original on April 27, 2021. Retrieved August 30, 2017.
- Leif, Johnson (November 2017). "How Unreal Tournament mods created a wave of successful indie studios". PC Gamer.
- Yee, Erica (December 2018). "The real reason Epic landed a $15 billion valuation is not Fortnite's viral video game success". CNBC. Archived from the original on November 9, 2021. Retrieved December 21, 2018.
- Alba, Michael (March 2020). "Unreal Engineering: How a Game Engine is Playing in New Industries". Engineering.com. Archived from the original on November 17, 2020. Retrieved November 15, 2020.