id Tech 4

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id Tech 4, frequently known as the Doom 3 engine, is a computer game engine developed by id Software and first used in the PC game Doom 3. The engine was designed by John Carmack, who also created previous engines such as those for Doom and Quake, which are also generally recognized as marking significant advances in the field.

[edit] History

The Doom 3 engine began as an enhancement to id Tech 3. Originally it was planned to be a complete rewrite of the engine's renderer, while still retaining other subsystems, such as file access, and memory management. After the new renderer was functional, however, the decision was made to switch from C to the C++ programming language, necessitating a complete restructuring and rewrite of the rest of the engine; today, while the Doom 3 engine contains code from id Tech 3, much of it has had to be rewritten.

Like its predecessors, id Tech 4 will eventually be released as open source. At the QuakeCon 2007, John Carmack the lead graphics engine developer at id, said to LinuxGames: "I mean I won't commit to a date, but the Doom 3 stuff will be open source." ^[1]

[edit] Hardware

A disadvantage of id Tech 4 was that it needed a high-end graphics processing unit (GPU), which was at least DirectX 8.0 compliant with fully programmable vertex and pixel shaders, such as the Nvidia GeForce 3 or ATI Radeon 8500, with at least 64 MB of VRAM. By E3 2002, the recommended GPU was the Radeon 9700 with 128 VRAM; while its DirectX 9.0 features are not necessary to render the game, its advanced architecture, 256-bit memory bus, and efficiency were needed to run Doom 3 at high detail and playable speed.[1]

id Tech 4 resulted in the obsolescence of DirectX 7.0 graphics chips such as the widespread GeForce 2 and Radeon 7200, as well as DirectX 6.0 chipsets such as RIVA TNT2 and Rage 128, and software rendering (with an integrated Intel GMA). Until the advent of id Tech 4, a powerful CPU was able to somewhat compensate for an older video card. While John Carmack initially warned gamers not to purchase the GeForce 4 MX (which casual consumers often confused with the DirectX 8.0 GeForce 4 Ti, though it was at best an improved DirectX 7.0 GeForce 2), its somewhat widespread adoption compelled id Software to enable Doom 3 to run on these cards, making it the only DirectX 7.0 chip capable of doing so. There have been cases of enthusiasts forcing Doom 3 to run on unsupported graphics chips, such as the long obselete Voodoo 2, but these are unable to render the per-pixel lighting and bump mapping.[2]

[edit] Features

The shadowing effects of the Unified lighting and shadowing engine are shown on the face and body of the zombies in this screenshot of Doom 3

[edit] Graphics

The Doom 3 engine added several new graphical features absent in its predecessor, id Tech 3. These included bump mapping, normal mapping, and specular highlighting. More features were added in the development of successive games, and in yet unreleased games using the Doom 3 engine, new features have been added or are planned to be added soon.

The primary innovation of the Doom 3 engine was its use of entirely dynamic per-pixel lighting, whereas previously, 3D engines had relied primarily on pre-calculated per-vertex lighting or lightmaps and Gouraud shading. While dynamic effects had been available before (such as dynamic moving lights), this effect merely changed the brightness of the vertices of the polygon with the pixels being simply interpolated between the three colours. The approach used in Doom 3 permitted more realistic lighting and shadows^[2] that just had been introduced in video games^[3].

[edit] Games using or licensing the Doom 3 engine

Unlike the preceding and widely-used id Tech 3 (Quake III Engine) and id Tech 2 (Quake II Engine), the Doom 3 engine has had somewhat less success in licensing to third parties. This is especially apparent in comparison to its closest competitor, the Unreal 3 engine. The unexpected long development time going into id Tech 4 did not help, as between 2002-2004, id Software had no equivalent to the Unreal 2 engine. Many who licensed the Unreal 2 engine were thus able to make the switch to Unreal 3 more easily.

While id Tech 4 had taken a new direction with its dynamic per-pixel lighting, this unconventional feature had steeper hardware requirements and was initially only useful in "spooky games" (until the MegaTexture addition), whereas an increasing number of developers preferred conventional engines that could render large outdoor areas. Aside from its dynamic lighting, id Tech 4 was still a DirectX 8 engine, while other rivals (such as the CryEngine, Lithtech Jupiter EX, and Source Engine) supported DirectX 9 features such as High dynamic range rendering, facial animations, and High Level Shader Language. Also notable was id Tech 4's relative lack of scalability compared to competing FPS engines which would have limited its potential audience; the Source Engine could still run on the older widespread DirectX 7 GPUs albeit without shaders being used.

• Doom 3 – id Software
  • Doom 3: Resurrection of Evil – Nerve Software
• Quake 4 – Raven Software
• Resident Evil: The Umbrella Chronicles – Capcom
• Prey – Human Head Studios
• Enemy Territory: Quake Wars – Splash Damage
• Return to Castle Wolfenstein II – Raven Software

[edit] MegaTexture rendering technology

The original version of the Doom 3 engine was criticized for its perceived inability to handle large outdoor areas. The MegaTexture technology addresses this issue by introducing a means to create expansive outdoor scenes. By painting a single massive texture (32,768×32,768 pixels, though it has been extended to larger dimensions in recent versions of the MegaTexture technology) covering the entire polygon map and highly detailed terrain, the desired effects can be achieved. The MegaTexture can also store physical information about the terrain such as the amount of traction in certain areas or indicate what sound effect should be played when walking over specific parts of the map. i.e. walking on rock will sound different from walking on grass.^[4] It is expected that this will result in a considerably more detailed scene than the majority of existing technologies, using tiled textures, allow. Currently, the only game that utilizes MegaTexture based on the Tech 4 engine is Enemy Territory: Quake Wars.

[edit] Techniques used in the Doom 3 engine

• Unified lighting and shadowing
• Shadow volume

[edit] See also

• First person shooter engine
• id Tech 2
• id Tech 3
• id Tech 5
• List of game engines
• Quake engine
• Quake (series)

[edit] References

• CNN - Life after "Doom"
• Gamespy article from which some information on MegaTexture was derived
• Article detailing some features of the Doom 3 engine
• [3]

[edit] External links

• Official MOD support website for the Doom 3 engine
• Technical Help Forum & Custom Content Creation
• Doom 3 engine reference material
• id Tech 4's ModDB page containing mod listing, tutorials, and more