Build engine

Build Engine is a first-person shooter engine created by Ken Silverman, author of ''Ken's Labyrinth'', for 3D Realms. Like the ''Doom'' engine, the Build Engine represents its world on a two-dimensional grid using closed 2D shapes called sectors, and uses simple flat objects called sprites to populate the world geometry with objects.

The Build Engine is generally considered to be a 2.5D engine since the basic world geometry is two-dimensional with an added height component, allowing each sector to have a different ceiling height and floor height. Playing the game shows that some floors can be lower and some can be higher; the same is true with ceilings (in relation to each other). Floors and ceilings can hinge along one of the sector's walls, resulting in a slope. With this information, the Build Engine renders the world in a way that looks three-dimensional, unlike modern game engines that create actual 3D environments.

Though the Build Engine achieved most of its fame as a result of powering the 1996 first-person shooter ''Duke Nukem 3D'', it was also used for many other games.

Technical features

Sectors

Sectors are the building blocks of a level's layout, consisting of a two-dimensional polygonal outline when viewed from above, with the top and bottom faces of the sector given separate altitudes to create a three-dimensional space. Hence, all walls are perfectly vertical—anything appearing otherwise is technically a sloped floor or ceiling. The word ''room'' can be used as a loose substitute to aid understanding, though one room in the game world can consist of many sectors, and parallaxed skies can give the illusion of being outdoors. Sectors can be manipulated in real-time; ''all'' of their attributes such as shape, height, and slope could be modified "on-the-fly" by games, unlike the earlier ''Doom'' engine. This allowed games to have destructible environments, such as those seen in ''Blood''. This technique is similar to the use of push walls in the earlier Apogee Software title '' Rise of the Triad'' which featured similar dynamic environments.

Developers of games based on the engine used special reserved "sprites" (game objects), often called "sector ", that, when given special tags (numbers with defined meanings), would allow the level designer to construct a dynamic world; similar tag information could be given to the sector walls and floor area to give a sector special characteristics. For example, a particular sector effector may let players fall through the floor if they walk over it and teleport them to another sector; in practice, this could be used to create the effect of falling down a hole to a bigger room or creating a body of water that could be jumped into to explore underwater. A sector could be given a tag that made it behave like an elevator or lift.

Sectors could overlap one another, provided they could not be seen at the same time (if two overlapping sectors were seen at the same time, a hall of mirrors effect resulted). This allowed the designers to create, for instance, air ducts that appeared to extend across the top of another room (however, doing so could be tricky for designers due to the 2D viewpoint used for much of the editing process). This allowed the designers to create worlds that would be physically impossible (e.g. a doorway of a small building could lead into a network of rooms larger than the building itself). While all these made the games using the engine appear to be 3D, it wouldn't be until later first-person shooters, such as '' Quake'', which used the ''Quake'' engine, that the engine actually stored the world geometry as true 3D information, making the creation of one area stacked atop another area in a single map very feasible.

Voxels

Later versions of Ken Silverman's Build Engine allowed game selected art tiles to be replaced by 3D objects made of voxels. This feature appeared too late to be used in ''Duke Nukem 3D'', but was seen in some of the later Build Engine games. ''Blood'' uses voxels for weapon and ammo pickups, power-ups, and eye-candy (such as the tombstones in the "Cradle to Grave" level, some chairs, and a crystal ball in "Dark Carnival"). ''Shadow Warrior'' makes even more advanced use of the technology, with voxels that can be placed on walls (all of the game's switches and buttons are voxels).

For several years, Ken worked on a modern engine based entirely on voxels, known as ''Voxlap''.

Room over room

One limitation of the Build Engine is that its level geometry is only capable of representing one connection between sectors for any given wall. Due to this, a structure as simple as a shelf with space both above and below it is impossible, though sometimes sprites or voxels can be substituted. Buildings with several floors are technically possible, but it is not possible for such a building to contain an external window directly above or below another window. In addition, some liberties will need to be taken with the staircases, elevators, and other methods of access for each floor.

Several Build Engine games (namely ''Shadow Warrior'', ''Blood'', and ''Redneck Rampage'') worked around this by displaying a "viewport" to another sector through an additional rendering pass. This technique, called ''room-over-room'' (ROR), appears seamless to the player. In addition to an expanded range of vertical construction, ROR was often used to give bodies of water translucent surfaces. ROR was never a feature of the Build Engine itself, but rather a "trick" that was created by game developers. A trick used in ''Duke Nukem 3D'' to get around this, as in the case of its opaque underwater sections, was to simply transport the player quickly to another region of the map made to mimic it, similar to the elevators from '' Rise of the Triad''.

In 2011, a feature was added to EDuke32 called ''true room over room'' (TROR), which allows multiple sectors to be stacked vertically so that each sector's wall has its own connection, enabling vertically-unrestricted structures. The difference between ROR and TROR is that TROR sectors physically overlap in the map data and editor (allowing for easy creation and visualization), rather than being drawn from separate locations using view portals, hence ''true'' room over room. TROR is a feature of the EDuke32 source port, not a game feature or trick.

List of Build Engine games

; Games that are built directly on the Build Engine
* ''Rock'n Shaolin: Legend of Seven Paladins 3D'' (1994) (only released in Taiwan and South Korea, illegally used an early version of the Build Engine)
* ''Witchaven'' (1995)
* ''William Shatner's TekWar'' (1995)
* ''Duke Nukem 3D'' (1996)
** ''Duke Nukem 3D: Plutonium PAK'' (1996)
** ''Duke Nukem 3D: Atomic Edition'' (1996)
** ''Duke!ZONE II'' (1997)
** ''Duke Xtreme'' (1997)
** ''Duke it Out in D.C.'' (1997)
** ''Duke Caribbean: Life's a Beach'' (1997)
** ''Duke: Nuclear Winter'' (1997)
* ''PowerSlave'' (''Exhumed'' in Europe and ''Seireki 1999: Pharaoh no Fukkatsu'' in Japan) (1996)
* '' Witchaven II: Blood Vengeance'' (1996)
* ''Blood'' (1997)
** ''Blood: Plasma Pak'' (1997)
** ''Blood: Cryptic Passage'' (1997)
* '' Shadow Warrior'' (1997)
** ''Shadow Warrior: Twin Dragon'' (1998)
** ''Shadow Warrior: Wanton Destruction'' (2005)

; Games that are based on the ''Duke Nukem 3D'' code
* ''Redneck Rampage'' (1997)
** ''Redneck Rampage: Suckin' Grits on Route 66'' (1997)
* ''Redneck Rampage Rides Again'' (1998)
* ''Redneck Deer Huntin''' (1998)
* '' Extreme Paintbrawl'' (1998)
* ''NAM'' (1998)
* ''Liquidator'' (1998) (only released in Russia, illegally used Build Engine and published by Akella