id Tech 2, popularly known as the Quake II engine, upgraded from Quake engine, is a game engine developed by id Software for use in their games, most notably Quake II. Since its release, the Quake II engine has been licensed for use in several other games.
One of the engine's most notable features was out-of-the-box support for hardware-accelerated graphics, specifically OpenGL, along with the traditional software renderer. Another interesting feature was the subdivision of some of the components into dynamic-link libraries. This allowed both software and OpenGL renderers, which were switched between by loading and unloading separate libraries. Libraries were also used for the game logic, for two reasons:
id could release the source code to allow modifications while keeping the remainder of the engine proprietary.
Since they were compiled for a native platform, instead of an interpreter, they could run faster than Quake's solution, which was to run the game logic (QuakeC) in a limited interpreter.
The level format, as with previous id Software engines, used BSP. The levels were lit through a lightmap method, in which light data for each surface is precalculated (this time, via a radiosity method) and stored as an image in the level file, which is then used to determine how much lighting intensity each model should receive, but not its direction.