CryEngine

Last updated
CryEngine
Developer(s) Crytek
Initial releaseMay 2, 2002;22 years ago (2002-05-02) [1]
Stable release
5.7.1 [2] / May 19, 2022;2 years ago (2022-05-19)
Written in C++ (Qt), Lua, C#
Platform
License Source-available commercial software with royalty model for commercial use
Website www.cryengine.com

CryEngine (stylized as CRYENGINE) is a game engine designed by the German game developer Crytek. It has been used in all of their titles with the initial version being used in Far Cry , and continues to be updated to support new consoles and hardware for their games. It has also been used for many third-party games under Crytek's licensing scheme, including Sniper: Ghost Warrior 2 and SNOW . Warhorse Studios uses a modified version of the engine for their medieval RPG Kingdom Come: Deliverance . Ubisoft maintains an in-house, heavily modified version of CryEngine from the original Far Cry called Dunia, which is used in their later iterations of the Far Cry series. The Dunia engine would in turn be further modified and used in games such as The Crew 2 . [7]

Contents

According to various anonymous reports in April 2015, CryEngine was licensed to Amazon for $50–70 million. [8] Consequently, in February 2016, Amazon released its own reworked and extended version of CryEngine under the name of Amazon Lumberyard. [9] [10]

Features

Versions

This diagram illustrates the development history of CryEngine game engine versions. Cryengine tree.svg
This diagram illustrates the development history of CryEngine game engine versions.

CryEngine 1

CryEngine 1 was first made and used for the first-person shooter video game Far Cry . It was originally developed by Crytek as a technology demo for Nvidia and, when the company saw its potential, it was turned into a game. When video cards with support for 3.0 pixel and vertex shaders were released, Crytek released version 1.2 of the engine which used some of the capabilities for better graphics. Later the company developed CryEngine version 1.3, which added support for HDR lighting. The engine has been licensed to NCsoft for their MMORPG, Aion: The Tower of Eternity . [22] On March 30, 2006, Ubisoft acquired all intellectual property rights to the Far Cry franchise and a perpetual license to use the Far Cry edition of CryEngine, known as the Dunia Engine. [23]

CryEngine 2

CryEngine 2 is used in Crytek's game Crysis , and an updated version in Crysis Warhead , a side story of Crysis. It was first licensed out to French company IMAGTP who specializes in architectural and urban-planning communication. The purpose of licensing the engine was to create a program to allow clients to see exactly what a building or other structure would look like before any actual construction was started. As of March 7, 2011, Simpson Studios has licensed CryEngine 2 out to use on a Massively Multiplayer Virtual World (MMVW) that takes place on a terraformed Mars. [24] On May 11, 2007, Crytek announced that they would be using the engine to create a game based on their new “intellectual property”. It is also confirmed that it would not be a part of Crysis and in fact may not even be a first-person shooter. On September 17, 2007, Ringling College of Art & Design became the first higher education institution in the world to license CryEngine 2 for educational purposes.

CryEngine 3 (3.0–3.5)

Crytek introduced CryEngine 3 at the 2009 Game Developers Conference, held from March 25 to March 27 and demonstrated it on the Xbox 360 and PlayStation 3 consoles. The new engine was being developed for use on Microsoft Windows, PlayStation 3, Xbox 360, and Wii U. As for the PC platform, the engine is said to support development in DirectX 9, 10, and 11. [25] [26] As of June 1, 2009, it was announced that Crysis 2 would be developed by Crytek on their brand-new engine. [27] CryEngine 3 was released on October 14, 2009. [28]

Family tree illustrates the history of CryEngine versions. Cryengine Family Tree 2016.svg
Family tree illustrates the history of CryEngine versions.

On March 1, 2010, a new tech demo of the engine was released for the i3D 2010 symposium, which demonstrates 'Cascaded Light Propagation Volumes for Real Time Indirect Illumination'. [29] On June 11, 2011, the Australian Defence Force revealed that Navy personnel would train on a virtual landing helicopter dock ship made using the CryEngine 3 software. [30] As of July 1, 2011, the Mod SDK version of CryEngine 3 specifically to create custom maps, mods and content for Crysis 2 is available on Crytek's website. Crytek also released a free-to-use version of the CryEngine for non-commercial game development. It was released as of August 17, 2011 under the name CRYENGINE® Free SDK. [31] [32]

Crytek announced on September 9, 2011, that they would be using CryEngine 3 to bring the original Crysis to consoles. [33] It was released for Xbox Live and PlayStation Network on October 4, 2011. [34]

CryEngine (3.6–4)

On August 21, 2013, Crytek rebranded CryEngine (starting from version 3.6.0) to simply "CryEngine", and announced that their next CryEngine would not be advertised with a version number. The reason for this decision was the claim that this new engine bears almost no similarity to previous CryEngine versions. However, the development kits available to licensees still use version numbers. [35] The new CryEngine version adds support for Linux [36] [37] and consoles such as the PlayStation 4, Xbox One, and Wii U. [38] Subsequent appearances at events have also featured the use of CryEngine on virtual reality systems, at GDC 2015 Crytek brought a demonstration 'Back To Dinosaur Island' to the event to showcase such. [39]

CryEngine V

On March 22, 2016, Crytek announced a new version of CryEngine, called CryEngine V. Additionally, a new licensing model was introduced with a "pay what you want" model for usage and access to the source code. [40] [41]

On September 21, 2017, CryEngine 5.4 was released, [42] adding the Vulkan API renderer as a beta, substance integration, [43] and other features including new C# templates, asset system updates, and new anti-aliasing techniques.

On March 20, 2018, Crytek changed the licensing from "pay what you want" to a 5% revenue-sharing model. [44]

In 2022 5.7 version was released with few new features as the features claimed to be in 5.7 were scrapped and moved to new CryEngine 6. 5.7 included Scaleform 4 support. The developers have stated that this will be the last version of CryEngine 5 and confirmed they are working on new iteration of CryEngine. The previous versions (before 5.7) were deprecated and can't be downloaded.

Development

The CryEngine software development kit (SDK), originally called Sandbox Editor, is the current version of the level editor used to create levels for CryEngine by Crytek. Tools are also provided within the software to facilitate scripting, animation, and object creation. It has been included with various Crytek games (including, but not limited to, Crysis and Far Cry ), and is used extensively for modding purposes. The editing style is that of the sandbox concept, with the emphasis on large terrains and a free style of mission programming. The editor can also construct indoor settings.

As opposed to editors like UnrealEd, which use a "subtractive" editing style that takes away areas from a filled world space, the Sandbox has an "additive" style (like Quake II ). Objects are added to an overall empty space. The Sandbox's concentration on potentially huge (in theory, hundreds of square kilometers) terrain, means that it uses an algorithmic form of painting textures and objects onto the landscape. This uses various parameters to define the distribution of textures or types of vegetation. This is intended to save time and make the editing of such large terrains feasible while maintaining the overall "real world" sandbox free roaming style. This is different from some editing styles that often use "fake backdrops" to give the illusion of large terrains.

In a fashion somewhat comparable to the 3D Renderer Blender, which can be used for game design, the Sandbox editor has the ability, with a single key press, for the editor to jump straight into the current design (WYSIWYP, "What You See Is What You Play" Feature). This is facilitated without loading the game as the game engine is already running within the editor. The "player" view is shown within the 3D portion of the Editor. The Editor also supports all the CryEngine features such as vehicles and physics, scripting, advanced lighting (including real time, moving shadows), Polybump technology, shaders, 3D audio, character inverse kinematics and animation blending, dynamic music, Real Time Soft Particle System and Integrated FX Editor, Deferred Lighting, Normal Maps & Parallax Occlusion Maps, and Advanced Modular AI System. [45]

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References

  1. "Crytek GmbH: Crytek announces its Game Engine CryENGINE". Wayback Machine . 2008-11-15. Archived from the original on 2008-11-15. Retrieved 2016-10-30.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
  2. "UPDATE Hotfix Today: CRYENGINE 5.7.1 LTS is here". Crytek. Archived from the original on 2022-06-06. Retrieved 2022-05-19.
  3. Wales, Matt (February 17, 2020). "Free-to-play first-person shooter Warface is now available on Switch". Eurogamer. Archived from the original on August 31, 2020. Retrieved February 17, 2020.
  4. "CryENGINE® 3 Equipped for Development on Sony Computer Entertainment's PlayStation®4". Crytek. 2013-07-06. Archived from the original on 2013-06-09. Retrieved 2013-07-24.
  5. "Wii U gets Crytek support with CryENGINE". ComputersAndVideoGames.com. 2011-06-14. Archived from the original on 27 December 2014. Retrieved 2012-09-08.
  6. "Crytek's CryENGINE® 3 Already Primed for Xbox One Development". Crytek. 2013-05-21. Archived from the original on 2013-06-08. Retrieved 2013-07-24.
  7. "Q&A: Inside the tools and techniques used to build The Crew 2's open world" . Retrieved 2024-09-15.
  8. Schreier, Jason (6 April 2015). "Sources: Amazon Spent Big Bucks On Crytek's Engine". Kotaku. Archived from the original on 2016-02-16. Retrieved 2016-02-10.
  9. Neltz, András (9 February 2016). "Amazon Releases Its Own Game Engine For Free". Kotaku. Archived from the original on 2016-12-12. Retrieved 2016-02-10.
  10. "Welcome to the Amazon GameDev Blog! | Amazon GameDev Blog". aws.amazon.com. 9 February 2016. Archived from the original on 2016-03-08. Retrieved 2016-02-10.
  11. 1 2 3 4 5 6 7 8 9 10 11 "CryENGINE 3 Technology". Archived from the original on 2012-03-01.
  12. 1 2 3 4 5 6 7 "CryENGINE 3 Technology". Archived from the original on 2012-10-04. Retrieved 2012-02-16.
  13. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 "CryENGINE 3 Technology". Archived from the original on 2012-04-22.
  14. 1 2 3 4 "CryENGINE 3 DX11 upgrade" (PDF). Archived from the original (PDF) on 2013-05-14. Retrieved 2012-02-16.
  15. 1 2 3 4 5 6 "CryENGINE 3 Technology". Archived from the original on 2012-03-15.
  16. 1 2 3 4 5 "CryENGINE 3 Technology". Archived from the original on 2012-03-26.
  17. 1 2 3 4 "CryENGINE 3 Technology". Archived from the original on 2012-01-01.
  18. 1 2 3 4 5 6 "CryENGINE 3 Technology". Archived from the original on 2012-03-01.
  19. "Water Volume Caustics". Archived from the original on 2017-01-01. Retrieved 2015-09-06.
  20. "UV Mapping Editor". Archived from the original on 2017-01-01. Retrieved 2015-09-09.
  21. "PBR". cryengine.com. Crytek. Archived from the original on 4 March 2016. Retrieved 21 December 2015.
  22. "NCSoft - AION". Crytek. Archived from the original on 2012-10-04. Retrieved 2012-08-09.
  23. "Ubisoft Acquires Far Cry IP and perpetual license of CryEngine". Archived from the original on 2009-01-07.
  24. "Welcome to Crytek". Archived from the original on 2008-04-22.
  25. "Crytek Announces CryENGINE 3". Crytek. 2009-03-11. Archived from the original on 2009-03-23. Retrieved 2009-03-12.
  26. Plunkett, Luke (2009-03-11). "PC Gaming Getting New Crytek Engine (Time To Upgrade)". Kotaku. Archived from the original on 2015-07-17. Retrieved 2009-03-12.
  27. "Crysis 2 teaser trailer". Crytek. 2009-06-01. Archived from the original on 2015-09-29. Retrieved 2009-06-08.
  28. "Crytek releases CryENGINE 3". Crytek. 2009-10-14. Archived from the original on 2013-04-27. Retrieved 2009-11-21.
  29. "Crytek 'i3D 2010' Tech Demo". Shacknews. 2011-02-10. Archived from the original on 2012-02-19. Retrieved 2012-09-08.
  30. "Avatars train on Navy's future ship". Australian Defence Force. 2011-06-11. Archived from the original on 2011-08-31. Retrieved 2011-06-11.
  31. "Free CryENGINE". MCV. develop online. 2010-04-12. Archived from the original on 2013-03-25. Retrieved 2010-04-12.
  32. "Crytek Releases CryENGINE®3 SDK Free-of-Charge". Crytek Official Website. 2011-08-17. Archived from the original on 2012-10-15. Retrieved 2011-08-25.
  33. "CRYTEK AND EA BRING CRYSIS TO CONSOLES". Crytek. Archived from the original on 2011-10-07. Retrieved 2011-10-10.
  34. "EA AND CRYTEK DELIVER CRYSIS TO CONSOLES TODAY". Crytek. Archived from the original on 2011-10-07. Retrieved 2011-10-10.
  35. "Public Release Notes". Crytek. Archived from the original on 2018-05-19. Retrieved 2015-03-15.
  36. "CRYENGINE adds Linux Support". Crytek. 2014-03-11. Archived from the original on 2021-01-13. Retrieved 2014-03-11.
  37. Peckham, Matt (2014-03-12). "Crytek Adding Linux Support for CryEngine Bodes Well for Steam OS". Time . US. Archived from the original on 2019-07-13. Retrieved 2014-08-13.
  38. Makuch, Eddie (August 21, 2013). "New CryEngine revealed". Gamespot. Archived from the original on September 25, 2013. Retrieved March 13, 2015.
  39. Eva, Kevin. "Crytek Unveils CryEngine Updates, Back To Dinosaur Island Demo". VRFocus. Archived from the original on 4 March 2016. Retrieved 4 March 2015.
  40. Schreier, Jason (2016-03-15). "Crytek's Video Game Engine Is Now Free". Kotaku. Archived from the original on 2016-05-10. Retrieved 2016-05-13.
  41. Prescott, Shaun (March 16, 2016). "CryEngine V releases today on a pay-what-you-want basis". PC Gamer . Archived from the original on May 18, 2016. Retrieved May 13, 2016.
  42. "CRYENGINE 5.4 Major Release". 2017-09-21. Archived from the original on 2018-12-12. Retrieved 2017-10-15.
  43. "5.4 Feature - Substance Import". CRYENGINE. 23 November 2017. Archived from the original on 2021-12-12. Retrieved February 18, 2020.
  44. "Crytek adopts royalties model as CryEngine 5.5 arrives". 2018-03-20. Archived from the original on 2018-09-13. Retrieved 2018-09-12.
  45. "What is the best game engine: is CryEngine right for you?". gamesindustry.biz. 16 January 2020. Archived from the original on 2021-10-28. Retrieved 2021-10-13.