View source for SoC Ideas LuaAI 2011

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=Description=
<h2>Extend Wesnoth's Lua AI support and improve Wesnoth's AI</h2>

More info at [[SoC_Ideas_LuaAI_2011]]

It is very important for Wesnoth to have a way of scripting AI without modifying the c++ source code. Some time ago, it was possible to use Python to code AIs, but it was removed due to security issues. Now, we have added Lua as a new way to script AI. The  core capabilities were already added, but we need to integrate Lua AI scripts better.

Wesnoth AI consists of different components. Each component is a c++ object, which provides an interface to allow the ai to delegate part of the turn sequence to that c++ object. But, that c++ object can be a proxy for code written in different language, such as formula_ai or lua. So, we have a lua engine - a c++ class which is responsible with creating c++ proxies for lua code snippets. This lua engine must provide access to all the information that the c++ AI knows - caches like 'attacks' and 'possible moves', values of aspects such as 'aggression' and 'caution', etc. So, there's a large number of AI support functions which we need to expose to lua code.

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=Required knowledge=
The student has to know or learn:
* Lua C++ api (src/scripting/lua.cpp is the example file)
* Basic WML (Wesnoth Markup language)
* Basic Lua 
* Wesnoth game concepts. Gameplay experience is very important to have or gain.

=Implementation plan=
To quote from Alpha Centauri, "Technological advance is an inherently iterative process. One does not simply take sand from the beach and produce a Dataprobe. We use crude tools to fashion better tools, and then our better tools to fashion more precise tools, and so on. Each minor refinement is a step in the process, and all of the steps must be taken. ".
* So, we firstly want to expose existing c++ things to lua.
* Then, we want to build a lua-based 'wesnoth lua ai standard library', a library of functions useful to an ai developer.
* Then, we want to build a library of high-level functions which will be directly usable by scenario developer, with the level of complexity like 'drop this 1-line macro here, set this unit variable there, and voila - the unit is now controlled by lua ai according to your wishes'
* example of such behavior are 'patrol', 'retreat', and 'guard' behaviors
* then, we want to improve the ai directly, areas like recruiting with multiple leaders, actually ''defending'' something, handling concepts like leadership,skirmish, illuminate, and other, even, created-from-WML, concepts
* then, we want to make sure that multiple ais can coordinate between themselves, and stick to a certain strategy in battle,as determined by situation and whims of scenario creator

== First step: expose existing c++ things to lua ==
* we need to expose AI aspects to lua
* we need to expose AI movement maps to lua ( std::multimap<map_location, map_location> , four of them)
* we need to expose AI target lists to lua (target is a marker on the game map)

when exposing things, we should make sure we provide a accessor which does the converted version and caches the converted version.
== Second step: wesnoth lua ai standard library ==
* we need to check and document ways for the AI author to include lua ai code in the scenario. for that, we should provide ways for the code to be injected by scenario, by era, by race, etc.
* we need to ensure that our .lua library code can be easily loaded by the AI engine. preferably, ensure that each library is only loaded once.

=Useful links=

* [[Customizing_AI_in_Wesnoth_1.8]]
* [[AI_Module]]
* [[LuaAI]]
* [[LuaWML]]

=Definition of Done=
All information that is possible to use in c++ AI, is possible to use in Lua AI with relatively same level of complexity for AI author.

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

=Possible pre-gsoc tasks=
We want to make it easy to write Lua AI. The best way to ensure that is to try to write some AI components, and see what's easy, what's hard, and what's missing. So, here are a few things that can be done to get you started and to allow to code some useful lua/c++ code which can be included in wesnoth lua ai standard library.

* Write the AI which can complete Scenario 1 of the '''Heir to the Throne''' campaign on easy difficulty.
* Write the AI which can complete Scenario 1 of '''The Hammer of Thursagan''' campaign on easy difficulty.
* Write a recruitment procedure for the AI which uses with multiple leaders intelligently
* Write a system to attach 'behavior instructions written in lua' to specific units
* Write a patrol formula in Lua    (march 13, taken by vdaras)
* Write a basic attack routine which allows to inject a Lua 'rate attack combination' function into it.
* Write a peacefull mob AI (independant units that flee all other unit and graze peacefully when far enough)
* Re-implement useful formula ai functions in lua.