For Alpha 5, there will be a random map generator integrated with the engine. This document describes the interaction between the engine and the random map scripts.

= Generating the Map =

When loading a scenario, the CMapReader class simply reads an XML file (with map settings, list of entities, and other textual data) together with a binary file called a PMP (which specifies height map and terrain textures). For a random map, there is obviously no predefined map data to load. Instead, the engine uses a new CMapGenerator class. The CMapGenerator needs the name of a random map script and some settings, such as number of players and their civs. These are selected during game setup.

== Engine-script interface ==

The CMapGenerator provides a minimal interface to the random map scripts. One is a global variable `g_MapSettings` which specifies all the map settings as created by game setup. CMapGenerator also exposes some JavaScript functions:
 * `RMS.LoadLibrary(name)` - load a library, choosing the API to which a random map script will have access, e.g. "rmgen".
 * `RMS.ExportMap(data)` - return generated map data from the scripts to the engine.
 * `RMS.SetProgress(percent)` - set the map generation progress percentage, so the loading screen progress bar can be updated. Percentage must be an integer 1-100.
 * `RMS.MaybeGC()` - possibly run the garbage collector.

== Data format ==
The data from a random map script must be in an exact format, independent of the methods used to generate it. This format can be specified in JSON as follows:
{{{
{
  "size": 128,
  "height": [ 1000, ... ]
  "seaLevel": 20.0,
  "textureNames": [ "medit_grass_field_a", ... ]
  "tileData": [ { "idx" : 0x0001, "priority" : 0 }, ... ]
  "entities": [ { "id" : 100, "name" : "units/hele_support_female_citizen", "x" : 102.4, "z" : 64.8, "angle" : 0.86}, ... ]
}
}}}
 * `size`: Integer. This is the size of the map in tiles.
 * `height`: Array of 16-bit unsigned integers. This is the height data for each tile of the map.
 * `seaLevel`: Float. This is the height of the sea, the value in the heightmap for which all lower terrain will be under water.
 * `textureNames`: Array of strings. This is the terrain textures used. They must be in the order in which they were defined (as they are referenced by tile data).
 * `tileData`: Array of tile descriptor objects. Tile descriptors reference the terrain texture(s) for a given tile.
 * `entities`: Array of entity objects. Entities specify something like a tree, unit, or building in the game.

=== Tile descriptor format ===
{{{
{
  "idx" : 8,
  "priority" : 0
}
}}}
 * `idx`: Integer. Texture ID to be used (value is referenced from `textureNames` array).
 * `priority`: Integer. Optional priority for texture blending (value of 0 is default). Considering adjacent tiles, the texture with higher priority will be blended on top of the tiles with lower priorities.

=== Entity format ===
{{{
  "id": 1034,
  "name": "units/hele_support_female_citizen",
  "x": 102.4,
  "z": 64.8,
  "angle": 0.86
}}}
 * `id`: Integer. Unique ID of this entity, used by the engine to identify each instance.
 * `name`: String. Template name of the entity, usually specifies faction and unit/building type for players, or special gaia templates.
 * `x`, `z`: Float. Position of the entity on the map (in XZ map coordinates; 4.0 map units = 1.0 tile unit).
 * `angle`: Float. Rotation of the entity about y-axis (vertical), in radians.

CMapReader is responsible for parsing this data and creating the map, in a process very similar to that for scenarios.