Cataclysm DDA uses a shifting coordinate system.

This means that when the player moves to a new submap, the (0, 0) coordinate moves from one submap to another, and the coordinates of all entities on the map are shifted to accommodate this.

Furthermore, the map is split into a hierarchical structure. At the top-level there are "overmaps", which are very large chunks of the gameworld. The overmap is split into overmap tiles. When you use 'm' to view the map in-game, what you see are overmap tiles. Each overmap tile is then again split into two submaps. See overmap and submap.

Parallel to this, there is the mapbuffer. The mapbuffer manages and stores all submaps. Note that this is separate to the overmap, which stores overmap tiles. The mapbuffer simply loads all submaps that have ever been created into memory and keeps them there in a list. It does not "sort" them into overmaps or anything like that.

Again parallel to this, there is map and g->m. A map contains a 2D pointer-array of submaps, for instance 11x11 submaps. These are usually centered around the player, which is the reason the coordinate system shifts. For all these submaps, it also caches additional data, such as lighting, scent, etc. This is basically where all the "on-screen" processing happens. Most of the source code modifies terrain, monsters and so on only by creating a map instance and using its methods.

Related Classes