Unreal Engine

The Unreal Engine is a game engine developed by Epic Games, first showcased in the 1998 first-person shooter game Unreal. Although initially developed for first-person shooters, it has been successfully used in a variety of other genres, including platformers, fighting games, MMORPGs, and other RPGs. Written in C++, the Unreal Engine features a high degree of portability, supporting a wide range of platforms.
The latest release is Unreal Engine 4, which launched in 2014 under a subscription model. Since 2015, it can be downloaded for free, with its source code available on GitHub. Epic allows for its use in commercial products based on a royalty model, typically asking developers for 5% of revenues from sales, though with the success of Fortnite, which has become a testbed for Unreal Engine for Epic, Epic waives this fee for developers that publish their games through the Epic Games Store. On May 13th, 2020, Epic announced that their portion of royalties for games developed in Unreal Engine are waived until developers have earned their first in revenue, retroactively applying to January 1st, 2020. Epic has announced Unreal Engine 5 to be released by late-2021.


First generation

The first-generation Unreal Engine was developed by Tim Sweeney, the founder of Epic Games. Having created editing tools for the shareware games ZZT and Jill of the Jungle, Sweeney began writing the engine in 1995 for the production of a game that would later become a first-person shooter known as Unreal. After years in development, it debuted with the game's release in 1998, although MicroProse and Legend Entertainment had access to the technology much earlier, licensing it in 1996. According to an interview, Sweeney "wrote 90 percent of the code in the engine." As with ZZT, he used the IBM Model M keyboard while programming.
written in Visual Basic.
Among its features were collision detection, colored lighting, and a limited form of texture filtering. The engine also integrated a level editor, UnrealEd, that had support for real-time constructive solid geometry operations as early as 1996, allowing mappers to change the level layout on the fly. Even though Unreal was designed to compete with id Software, developers of Doom and Quake, John Carmack complimented the game for the use of 16-bit color while remarking its implementation of ambient effects such as volumetric fog. "I doubt any important game will be designed with 8-bit color in mind from now on. Unreal has done an important thing in pushing toward direct color, and this gives the artists a lot more freedom," he said in an article written by Geoff Keighley for GameSpot. "Light blooms , fog volumes, and composite skies were steps I was planning on taking, but Epic got there first with Unreal," he said, adding: "The Unreal engine has raised the bar on what action gamers expect from future products. The visual effects first seen in the game will become expected from future games." Another notable feature was the introduction of real-time direct illumination in 1995.
At first, the engine relied completely on software rendering, meaning the graphics calculations were handled by the CPU. However, over time, it was able to take advantage of the capabilities provided by graphics cards, a process that required Sweeney to rewrite the core rendering algorithm several times. As a result, software and hardware rendering would coexist in the engine, with the latter focusing on the Glide API, specially designed for 3dfx accelerators. While supported, OpenGL and Direct3D reported a slower performance compared to Glide due to their deficiency in texture management. With regard to audio, Epic employed the Galaxy Sound System, a software programmed in assembly language that integrated both EAX and Aureal technologies, and allowed the use of tracker music, which gave level designers flexibility in how the soundtrack was played at a specific point.
Unreal was noted for its technical innovations, but Sweeney recognized in an interview with Eurogamer that many aspects of the game were unpolished, citing complaints about its high system requirements and online gameplay issues. The development of Unreal Tournament enabled Epic to address these points, incorporating several enhancements in the engine intended to optimize performance on low-end machines and improve the networking code, while refining the artificial intelligence for bots to display coordination in team-based environments. In addition to being available on Microsoft Windows, Linux, Mac and Unix, the engine was ported through Unreal Tournament to the PlayStation 2 and, with the help of Secret Level, to the Dreamcast.
By late 1999, The New York Times indicated that there had been sixteen external projects using Epic's technology, including Deus Ex, The Wheel of Time, and Duke Nukem Forever, the latter of which was originally based on the Quake II engine. Unlike id Software, whose engine business only offered the source code, Epic provided support for licensees and met with them to discuss improvements to its game development system. While it cost around $3 million to produce and licenses for up to $350,000, Epic gave players the ability to modify its games with the incorporation of UnrealEd and a scripting language called UnrealScript, sparking a community of enthusiasts around a game engine built to be extensible over multiple generations of games.

Unreal Engine 2

In October 1998, IGN reported, based on an interview with affiliate Voodoo Extreme, that Sweeney was doing research for his next-generation engine. With development starting a year later, the second version made its debut in 2002 with America's Army, a free multiplayer shooter developed by the U.S. Army as a recruitment device. Epic would later release Unreal Championship on the Xbox, with it being one of the first games to utilize Microsoft's Xbox Live.
Though based on its predecessor, this generation saw a notable advance in rendering terms as well as new improvements to the tool set. Capable of running levels nearly 100 times more detailed than those found in Unreal, the engine integrated a variety of features, including a cinematic editing tool, particle systems, export plug-ins for 3D Studio Max and Maya, and a skeletal animation system first showcased in the PlayStation 2 version of Unreal Tournament. Additionally, the user interface for UnrealEd was rewritten in C++ using the wxWidgets toolkit, which Sweeney said was the "best thing available" at the time.
Physical simulations, such as ragdoll player collisions and arbitrary rigid body dynamics, were powered by the Karma physics engine. With Unreal Tournament 2004, vehicle-based gameplay was successfully implemented, enabling large-scale combat. While Unreal Tournament 2003 had support for vehicle physics through the Karma engine, as demonstrated by a testmap with a "hastily-constructed vehicle", it wasn't until Psyonix created a modification out of Epic's base code that the game received fully coded vehicles. Impressed by their efforts, Epic decided to include it in its successor as a new game mode under the name of Onslaught by hiring Psyonix as a contractor. Psyonix would later develop Rocket League before being acquired by Epic in 2019.
A specialized version of UE2 called UE2X was designed for on the original Xbox platform, featuring optimizations specific to that console. In March 2011, Ubisoft Montreal revealed that UE2 was successfully running on the Nintendo 3DS via Tom Clancy's Splinter Cell 3D.

Unreal Engine 3

Screenshots of Unreal Engine 3 were presented in 2004, at which point the engine had already been in development for over 18 months. The engine was based on the first-generation, but contained new features. "The basic architectural decisions visible to programmers of an object-oriented design, a data-driven scripting approach, and a fairly modular approach to subsystems still remain . But the parts of the game that are really visible to gamers –the renderer, the physics system, the sound system, and the tools– are all visibly new and dramatically more powerful," said Sweeney. Unlike Unreal Engine 2, which still supported a fixed-function pipeline, Unreal Engine 3 was designed to take advantage of fully programmable shader hardware. All lighting and shadowing calculations were done per-pixel, instead of per-vertex. On the rendering side, Unreal Engine 3 provided support for a gamma-correct high-dynamic range renderer. The first games released using Unreal Engine 3 were Gears of War for Xbox 360, and RoboBlitz for Windows, which were both released on November 7, 2006.
Initially, Unreal Engine 3 only supported Windows, PlayStation 3, and Xbox 360 platforms, while iOS and Android were added later in 2010, with Infinity Blade being the first iOS title and Dungeon Defenders the first Android title. In 2011, it was announced that the engine would support Adobe Flash Player 11 through the Stage 3D hardware-accelerated APIs and that it was being used in two Wii U games, ' and '. In 2013, Epic teamed-up with Mozilla to bring Unreal Engine 3 to the web; using the asm.js sublanguage and Emscripten compiler, they were able to port the engine in four days.
Throughout the lifetime of UE3, significant updates were incorporated, including improved destructible environments, soft body dynamics, large crowd simulation, iOS functionality, Steamworks integration, a real-time global illumination solution, and stereoscopic 3D on Xbox 360 via TriOviz for Games Technology. DirectX 11 support was demonstrated with the Samaritan demo, which was unveiled at the 2011 Game Developers Conference and built by Epic Games in a close partnership with NVIDIA, with engineers working around the country to push real-time graphics to a new high point.

Unreal Development Kit

While Unreal Engine 3 was quite open for modders to work with, the ability to publish and sell games meant using UE3 was restricted to licensees of the engine. However, in November 2009, Epic released a free version of UE3's SDK, called the Unreal Development Kit, that is available to the general public.
In December 2010, the kit was updated to include support for creating iOS games and apps. OS X compatibility followed in the September 2011 release.

Unreal Engine 4

Development on Unreal Engine 4 began in 2003, according to Mark Rein, the vice-president of Epic Games. In early 2008, Sweeney revealed in an interview that he was basically the only person working on the engine, although he stated the research and development team would expand over time, designing the engine in parallel with the efforts by the UE3 team. In February 2012, Rein said "people are going to be shocked later this year when they see Unreal Engine 4"; Epic unveiled UE4 to limited attendees at the 2012 Game Developers Conference, and a video of the engine being demonstrated by technical artist Alan Willard was released to the public on June 7, 2012, via GameTrailers TV.
One of the major features planned for UE4 was real-time global illumination using voxel cone tracing, eliminating pre-computed lighting. However, this feature, called Sparse Voxel Octree Global Illumination, has been replaced with a similar but less computationally expensive algorithm due to performance concerns. UE4 also includes the new "Blueprints" visual scripting system, which allows for rapid development of game logic without using code, resulting in less of a divide between technical artists, designers, and programmers.
On March 19, 2014, at the Game Developers Conference, Epic Games released Unreal Engine 4 through a new licensing model. For a monthly subscription at, developers were given access to the full version of the engine, including the C++ source code, which could be downloaded via GitHub. Any released product was charged with a 5% royalty of gross revenues. The first game released using Unreal Engine 4 was Daylight, developed with early access to the engine and released on April 29, 2014.
On September 4, 2014, Epic released Unreal Engine 4 to schools and universities for free, including personal copies for students enrolled in accredited video game development, computer science, art, architecture, simulation, and visualization programs. On February 19, 2015, Epic launched Unreal Dev Grants, a $5 million development fund aiming to provide grants to creative projects using Unreal Engine 4.
In March 2015, Epic released Unreal Engine 4, along with all future updates, for free for all users. In exchange, Epic established a selective royalty schedule, asking for 5% of revenue for products that make more than $3,000 per quarter. Sweeney stated that when they moved to the subscription model in 2014, use of Unreal grew by 10 times and through many smaller developers, and believed that they would draw even more uses through this new pricing scheme.
In an attempt to attract Unreal Engine developers, Oculus VR announced in October 2016 that it will pay royalty fees for all Unreal-powered Oculus Rift titles published on their store for up to the first $5 million of gross revenue per game.
To prepare for the release of its free-to-play battle royale mode in Fortnite in September 2017, Epic had to make a number of Unreal Engine modifications that helped it to handle a large number of connections to the same server while still retaining high bandwidth, and to improve the rendering of a large open in-game world. Epic said it would incorporate these changes into future updates of the Unreal Engine.
With the opening of the Epic Games Store in December 2018, Epic will not charge the 5% revenue fee on games that use the Unreal Engine and released through the Epic Games Stores, absorbing that cost as part of the base 12% cut Epic is taking to cover other costs.
Effective May 13, 2020, and retroactive to January 1, 2020, the royalty exemption amount is increased to $1,000,000 USD in lifetime gross revenue per title.

Supported platforms

Unreal Engine 5

Unreal Engine 5 was revealed on May 13, 2020 with expected launch in late-2021, supporting all existing systems including the next-generation consoles PlayStation 5 and Xbox Series X. Work on the engine started about two years prior to its announcement. Among its major features include Nanite, an engine that allows for high-detailed photographic source material to be imported into games. The Nanite virtualized geometry technology allows Epic to take advantage of its past acquisition of Quixel, the world's largest photogrammetry library in 2019. The goal of Unreal Engine 5 was to make it as easy as possible for developers to create detailed game worlds without having to spend excessive time on creating new detailed assets, allowing the engine software to handle these factors. Nanite can import nearly any other pre-existing three-dimension representation of objects and environments, including ZBrush and CAD models, allowing the use of film-quality assets. Nanite automatically handles the levels of detail of these imported objects appropriate to the target platform and draw distance, a task that an artist would have had to perform otherwise. Lumen is another component described as a "fully dynamic global illumination solution that immediately reacts to scene and light changes". Lumen eliminates the need for artists and developers to craft a lightmap for a given scene, but instead calculates light reflections and shadows on the fly, thus allowing for real-time behavior of light sources. Additional components include Niagara for fluid and particle dynamics and Chaos for a physics engine.
With potentially tens of billions of polygons present on a single screen at 4k resolution, Epic also developed the Unreal Engine 5 to take advantage of the upcoming high-speed storage solutions with the next-generation console hardware that will use a mix of RAM and custom solid-state drives. Epic had worked closely with Sony in optimizing Unreal Engine 5 for the PlayStation 5, with Epic helping Sony with the console's storage architecture, which Sweeney said is "far ahead of anything you can buy on anything on PC for any amount of money right now." To demonstrate the ease of creating a detailed world with minimal effort, the May 2020 reveal of the engine showcased a demo called "Lumen in the Land of Nanite" running on a PlayStation 5 that was built by mostly pulling assets from the Quixel library and using the Nanite, Lumen, and other Unreal Engine 5 components to create a seemingly-realistic cave setting that could be explored. Epic affirmed that Unreal Engine 5 would be fully supported on the Xbox Series X as well, but had been focused on the PlayStation 5 during the announcement as a result of their work with Sony in the years prior. Epic plans to use Fortnite as a testbed for Unreal Engine 5 to showcase what the engine can do to the industry, with the game expected to use the engine by mid-2021. Ninja Theory's will also be one of the first games to use Unreal Engine 5.
Unreal Engine 5 will retain the current royalty model, with developers returning 5% of gross revenues to Epic Games, though this fee is forgiven for those that release their games on the Epic Games Store. Further, Epic announced alongside Unreal Engine 5 that they will not take any fee from games using any version of Unreal Engine for the first in gross revenue, retroactive to January 1, 2020.


UnrealScript 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. The UnrealScript interpreter was programmed by Sweeney, who also created an earlier game scripting language, ZZT-oop.
Similar to Java, UnrealScript was object-oriented without multiple inheritance, 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++. Visual scripting would be supported by the Blueprints Visual Scripting system, a replacement for the earlier Kismet visual scripting system.


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. 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%.