Composite textures, created through a TEXTUREx or TEXTURES lump, use patches to build the finished textures. Furthermore, ZDoom does require patches to be properly namespaced in PK3 archives. A few old utilities however assume that the P_ markers are needed and can be relied upon.
In WAD files, patches are therefore, along with other graphics that are neither sprites nor flats, in the global namespace. Although the IWADs all make use of P_START/ P_END markers, the original engines do not actually use these markers. There exist therefore the need to make a distinction between the two different things that 'patch' may mean in ZDoom: the namespace and the picture format. ZDoom, however, features a texture manager that allows to use any of the supported image formats for any purpose. Since the original Doom renderer draws floors and ceilings horizontally (line after line), but walls and sprites vertically (column after column), the native Doom format for patches is a column-major format. In the original Doom engine, a patch is an image that is used as the building block for a composite texture (also called a multipatch texture). For more information on this article, visit the Patch page on the Doom Wiki.
