Editing Build (game engine) (section)

== 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 [[face (geometry)|faces]] of the sector given separate [[altitude]]s to create a three-dimensional space.<ref name=Retroact2>{{cite magazine |last=Rule|first=Duncan |url=https://issuu.com/retroaction/docs/retroaction_issue_2|title=Building Classics |magazine=Retroaction|issue=2|date=Summer 2009|pages=8–15|access-date=26 December 2021}}</ref> 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 [[parallax]]ed 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|''Doom'' engine]]. This allowed games to have destructible environments, such as those seen in ''[[Blood (video game)|Blood]]''.<ref name=Retroact2/> 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 {{sic|effectors}}", 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).<ref name="rpshobeauty">{{cite web |last=Zak |first=Robert |date=13 April 2016 |title=The Beauty of the Build Engine |url=https://www.rockpapershotgun.com/2016/04/13/build-engine-duke-nukem-blood-shadow-warrior/ |publisher=[[Rock, Paper, Shotgun]]}}</ref> 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 (video game)|Quake]]'', which used the [[Quake engine|''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 [[voxel]]s. 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.