Slope

Slopes are an editing feature supported by some Doom source ports which allows the designer to make surfaces that are at angles other than horizontal or vertical. Sloped surfaces in a 2.5D system have issues that are mostly irrelevant in true 3D engines such as Quake.

In a 2.5D map system, depending on the implementation, it can be either floors or walls that are sloped: for example, in Duke Nukem 3D, the slopes are applied to the walls. Doom source ports however usually prefer to slope the floors and ceilings, as it is technically more efficient. Regardless of the implementation, the greater the angle between the surface and its "normal" (horizontal or vertical) alignment, the more stretched its texture. Source ports may provide mechanisms to alleviate the problem, for example the Sector_Set*Scale specials in ZDoom.

A full implementation of sloped surfaces includes changes to both the renderer and the physics code. The former is relatively simpler than the latter, since even slight changes in the physics code risk breaking demo compatibility.

Ports with slopes

 * EDGE (renderer only)
 * Eternity Engine (renderer only)
 * GZDoom
 * Skulltag
 * Vavoom
 * ZDoom