id Game Engine Source Code

The first 3D first-person shooter (FPS) game is generally accepted to be Castle Wolfenstein 3D (1992). Written by id Software of Texas for the PC platform, this game led the game industry in a new and exciting direction.

First-person games are typically some of the most technologically challenging to build. They aim to provide their players with the illusion of being immersed in a detailed, hyperrealistic world. It is not surprising that many of the game industry’s big technological innovations arose out of the games in this genre. Some of the complexities in FPS style games often include managing binary space partitioning (BSP) trees, portal-based rendering systems, frustum cull (i.e., removing objects that the camera cannot "see" to improve rendering time), spatial subdivision data structures, dynamic lighting systems and more.

Outdoor FPS games use other kinds of rendering optimizations such as occlusion culling, or an offline sectorization of the game world with manual or automated specification of which target sectors are visible from each source sector.

Digging into this technology, you can find the source code to Quake I, II, III, Doom, Wolfenstein and more id based games are freely available. The original Quake engines are reasonably well architected and “clean” (although they are of course a bit outdated and written entirely in C). These code bases serve as great examples of how industrial-strength game engines are built. The full source code to several id games are available on github at https://github.com/id-Software

You can actually build the code using Microsoft Visual Studio and run the game under the debugger using the real game assets from the disk. This can be incredibly instructive. You can set break points, run the game, and then analyze how the engine actually works by stepping through the code.

For a nice overview of the FPS genre, see http://en.wikipedia.org/wiki/First-person_shooter