Build Engine

The Build engine is a first-person shooter engine created by Ken Silverman 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.

It is generally considered to be a 2.5D engine as the basic world geometry is two-dimensional, with an added height component, allowing each sector to have a different ceiling and floor height, and allowing them to be angled along one line of the sector. The engine renders the world in a way that looks three-dimensional; however, the sizing for perspective only depends on the horizontal distance. This is noticeable in that wall vertices are always straight vertical lines on screen, regardless of the angle of view. Therefore, with no vertical distance parameters (only horizontal), this can cause small size distortion when looking up and down but generally it is barely noticeable. However, this distortion can be severe if the player is looking at a structure that is very tall. As such, most Build games restrict objects' vertical height to a fairly limited range.