View source for SoC Ideas Persistent Gameworld

{{Template:SoC2010Idea}}
=Description=
<h2>Implement persistent storage of gameworld data between semi-related scenarios</h2>
Page for the idea: [[SoC_Ideas_Persistent_Gameworld]]

Allow WML authors to store/access persistent data 'in context' of a specific campaign/add-on/group of addons/ group of games. This will allow things like 'achievements' or 'massive multiplayer campaigns' to work.

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=Additional information=
Right now, WML can store/load information inside a save game. a save game is a single thread of play through one or multiple scenarios.

We would like to make it possible to store (save/load) information inside a different context, such as 'shared data for all games played locally on a particular map/campaign/addon/wesnoth installation'. This will allow WML authors to implement many interesting things like 'achievements' system for their campaign, or additional replayability things.

Also, we would like to make it possible to store such information for MP games. This will allow things like 'massive multiplayer' games with persistent gameworld - where each MP game changes some data for one of  'global' massive multiplayer campaigns.

'''Example:'''
Imagine a game where there's a 'game master' - who creates a scenario, where you, for example, as a captain of a royal army, play for loyalists vs orcs. and then, if you win, the 'game master' changes the 'geopolitical map' to represent the fact that the border was defended, and orcs were defeated. Or imagine several games played in parallel, where you can transition from one game to another 'right-in-the-middle' (e..g, the gamemaster can store your units in one game and spawn them in another). and, it will not be hardcoded in c++ code. Every rule, every fantasy, can be achieved in wml, if we give a 'language' for it and implement engine support.

=Definition of Done=
WML authors are able to store and load WML snippets in their core campaigns/addons/groups of addons/groups of games. It is possible to use this system for displaying per-addon 'Achievements'. 'massive multiplayer' games with persistent gameworld are possible to code using WML and possible to host using stock wesnoth multiplayer server.

=WML Syntax=
 [get_global_variable]
  side=1
  namespace=my_addon
  from_global=my_variable_name
  to_local=foo
 [/get_global_variable]

 [set_global_variable]
  side=1
  namespace=my_addon
  from_local=my_variable_name
  to_global=foo
 [/set_global_variable]

 [clear_global_variable]
  side=1
  namespace=my_addon
  global=foo
 [/clear_global_variable]

Notes:

There might be need for a [global_variable] tag for use in an [if] (similarly to how [variable] works there)

=Whom to ask about this=
Ask Crab_ on #wesnoth-dev