Jedi is a game engine developed primarily by Ray Gresko for LucasArts. It is extremely similar to the Build engine used in Duke Nukem 3D. While not a true 3D engine, it supported a three-dimensional environment with no limitations in the 3rd dimension (Z). In Doom, environments or levels were limited to existing in the X-Y plane only — levels were laid out two-dimensionally: while floor and ceiling heights could differ, areas could not overlap vertically. The Jedi Engine had support for areas or rooms (called "sectors") on top of one another, a trait that it shared with the Build engine. In the Dark Forces revision of the engine, the renderer could not display two rooms situated on top of each other at the same time. This capability was added for Outlaws.