The CRX game engine is an opensourced, cross platform program that was derived from id Software

Id Software

Id Software is an American video game development company with its headquarters in Richardson, Texas. The company was founded in 1991 by four members of the computer company Softdisk: programmers John Carmack and John Romero, game designer Tom Hall, and artist Adrian Carmack...

's GPL code releases by COR Entertainment. The engine is primarily used for the game CodeRED: Alien Arena

CodeRED: Alien Arena

Alien Arena is a free, stand-alone first-person shooter computer game based on source code released by id Software. Begun by COR Entertainment in 2004, the game combines a 1950s-era sci-fi atmosphere with gameplay similar to the Quake, Doom, and Unreal Tournament series...

. The engine makes use of Quake II

Quake II

Quake II, released on December 9, 1997, is a first-person shooter computer game developed by Id Software and distributed by Activision. It is not a sequel to Quake; it merely uses the name of the former game due to Id's difficulties in coming up with alternative names.The soundtrack for Quake II...

 data formats such as .md2 and the BSP map format as well as others such as the skeletal Inter-Quake Model(IQM), and ogg/vorbis audio. The engine runs on Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

, Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

, and FreeBSD

FreeBSD

FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...

. The engine has also been ported to MacOS by third-parties.

Technical specifications

CRX makes use of GLSL

GLSL

OpenGL Shading Language , is a high-level shading language based on the syntax of the C programming language...

 for per-pixel lighting, parallax mapping

Parallax mapping

Parallax mapping is an enhancement of the bump mapping or normal mapping techniques applied to textures in 3D rendering applications such as video games...

, normal mapping

Normal mapping

In 3D computer graphics, normal mapping, or "Dot3 bump mapping", is a technique used for faking the lighting of bumps and dents. It is used to add details without using more polygons. A common use of this technique is to greatly enhance the appearance and details of a low polygon model by...

, and specular highlights for the majority of its rendered surfaces as well as post processing effects. The engine supports the use of 32-bit TARGA

Truevision TGA

Truevision TGA, often referred to as TARGA, is a raster graphics file format created by Truevision Inc. . It was the native format of TARGA and VISTA boards, which were the first graphic cards for IBM-compatible PCs to support Highcolor/truecolor display...

 with alphamasking, as well as JPEG

JPEG

In computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....

 image formats. Stencil buffer shadows are used as simple planar shadows, as well as blurred stencil volumes. Dynamic shadows for all geometry are created by shadow mapping

Shadow mapping

Shadow mapping or projective shadowing is a process by which shadows are added to 3D computer graphics. This concept was introduced by Lance Williams in 1978, in a paper entitled "Casting curved shadows on curved surfaces"...

. Fog, weather effects, textured particles, lens flare

Lens flare

Lens flare is the light scattered in lens systems through generally unwanted image formation mechanisms, such as internal reflection and scattering from material inhomogeneities in the lens. These mechanisms differ from the intended image formation mechanism that depends on refraction of the image...

s, and light volumes are among some of the other renderer features. The audio is handled by OpenAL

OpenAL

OpenAL is a cross-platform audio API. It is designed for efficient rendering of multichannel three dimensional positional audio. Its API style and conventions deliberately resemble those of OpenGL.- History :...

 by Creative Labs, and supports effects such as Doppler. The Open Dynamic Physics Engine is used to handle the built in ragdoll physics

Ragdoll physics

In computer physics engines, ragdoll physics is a type of procedural animation that is often used as a replacement for traditional static death animations.-Introduction:Early video games used manually-created animations for characters' death sequences...

.

The netcode is based on the original Quake 2 source, with some changes such as antilag

Lag

Lag is a common word meaning to fail to keep up or to fall behind. In real-time applications, the term is used when the application fails to respond in a timely fashion to inputs...

 (backwards reconciliation) and packet prioritorization, and [Http] downloading of media content. A built-in server browser assists users in finding online games.

Critical acclaim

While CRX isn't as widely used as some other Quake-based gaming engines, it has received its share of press, mostly through tech reviews of CodeRED: Alien Arena

CodeRED: Alien Arena

Alien Arena is a free, stand-alone first-person shooter computer game based on source code released by id Software. Begun by COR Entertainment in 2004, the game combines a 1950s-era sci-fi atmosphere with gameplay similar to the Quake, Doom, and Unreal Tournament series...

and gaming engine tech articles.