Editing Startbox API

== Start boxes ==

Each team has a defined starting area in which its players can spawn their commanders—these are called '''start boxes'''. Map makers can define how these areas look by including a configuration file inside their map archive.

== The config file ==

The file that you need to include is
 mapconfig/map_startboxes.lua

It consists of Lua code which returns 2 tables: one with the start box layout for the current match and one that contains possible box counts.

For [[#Examples|examples]] see the bottom of this page.

== Box counts ==

Let's start from the last table because it is the simplest. This is just a list of how many teams the map is designed for.

Let's take [http://zero-k.info/Maps/Detail/8162 Throne] map as an example. It has an outer ring with 7 starting areas, so it can be played as a 7-team <abbr title="free for all">FFA</abbr>. There are also rings with 3 and 5 areas so 3- and 5-team FFAs are also possible setups. Finally, you could play a duel between any two positions from the same ring. (The real Throne config is a fair bit more complicated than that, but you get the idea.)

Thus, the possible team counts are 2, 3, 5, and 7. Let's define a Lua table for that:
<syntaxhighlight lang="lua">local playercounts = {2, 3, 5, 7}</syntaxhighlight>

This is mostly important for fancy FFA maps. Simple duel/teamgame maps will usually just have 2 as the only value here:
<syntaxhighlight lang="lua">local playercounts = {2}</syntaxhighlight>

== The boxes ==

Now, the most tedious part. The boxes do not need to actually be boxes, they can be any arbitrary shape (even concave or disjoint). This is achieved by having the boxes defined as a set of polygons.

There is a widget which lets you draw the polygons in-game, it's called "Startbox Editor" and is under the "For Developers" section in the widget list (press {{key combo|Alt|F11}} to open the list, and don't touch anything else in there unless you know what you're doing).

To draw a polygon using the left mouse button—either drag a line or click points:

[[File:Startbox API 1.jpg]]

Once you draw a full loop, press the right mouse button to close it. Make sure the line does not cross itself. Finished polygons are a bit darker.

[[File:Startbox API 2.jpg]]

Now you can add another polygon if you want. These will all be a part of the same team.

[[File:Startbox API 3.jpg]]

If you want to delete the last created polygon, press {{key press|D}}.
Once you are satisfied with the area, press {{key press|S}}. Now you can draw the area for another team.

Once you create all the boxes, go to your Spring directory and find the infolog. There you will see a bunch of code like
<syntaxhighlight lang="lua">boxes = {
     stuff
},</syntaxhighlight>

Each of those tables is a team's start box. The config is an array of each team's start box data. The box data from the generator will go to a team's config entry. Like this:
<syntaxhighlight lang="lua">local main_config = {
     {
         boxes = {
             stuff
         },
         -- more entries will go there later!
     },
     
     -- another team's box data
     {
         boxes = {
             stuff
         },
     },
}</syntaxhighlight>

The layout is a normal Lua table so you can use all the usual table manipulation methods. For example, you could add more areas based on how many people there are, or generate them dynamically.

== The recommended start points ==

This sub-table defines recommended start points within each box. These are points on which CAI bots will spawn. The first point is special: human players who did not pick start position will also spawn here and so will any extra CAI if there are more of them than the spots; as such having at least one start point in each box is mandatory. These points are also marked on people's UI as circles.

Defining these is very simple. It's very similar to how start areas were defined. In game, you can hold Space over a point to see its coordinates. These are written down for boxes similarly to the areas:
<syntaxhighlight>local main_config = {
     {
         boxes = {
             stuff
         },
         startpoints = {
             {123, 456}, -- X, Z
             {654, 321},
             -- as many as you want, it's good if there are as many as you want people per team
         },
     },
     {
         boxes = {
             stuff
         },
         startpoints = {
             {789, 789},
             {987, 987},
         },
     },
}</syntaxhighlight>

Of course, the start positions should match the areas, though they don't have to.

== Team names ==

You can give each team a name, alongside a shorter backup if the first one is too large. Here's how:

<syntaxhighlight lang="lua">{
     boxes = { stuff },
     startpoints = { stuff },
     nameLong = "Southwest",
     nameShort = "SW",
}</syntaxhighlight>

It serves to identify the team, so while it's good to use something that describes placement, you can get creative. For example:
* "North", "Southeast"
* "5 o'clock"
* real-world style maps could have names like "Russia" or "America"
* asymmetric maps can use landmarks, for example "Lake" vs "Desert"
* for missions, it's good to use storyline names, e.g. "Empire" vs "Dynasty"

== Summary ==

Now just return the ''config'' table and the ''playercounts'' table.
<syntaxhighlight lang="lua">return main_config, playercounts</syntaxhighlight>

The exact format for the config table that should get returned is

<syntaxhighlight lang="lua">{
     { -- a single team's data
         boxes = {
             { -- a polygon
                 {123, 456}, -- a vertex of the polygon. X, Z.
                 {234, 567}, -- another vertex
                 {345, 678},
                 -- more vertices
             },
             { -- another polygon
                 -- vertices
             },
             -- more polygons
         },
         startpoints = {
             {123, 456}, -- X, Z
             {654, 321},
             -- more points
         },
         nameLong = "longer string with team name",
         nameShort = "short",
     },
     { -- another team's data
         boxes = { ... },
         startpoints = { ... },
         nameLong = "...",
         nameShort = "...",
     },
     -- more teams
}</syntaxhighlight>

== Advanced stuff ==
The config has access to Spring Lua API, so it is possible to do a lot of dynamic things. In particular, you can use <syntaxhighlight lang="lua" inline>math.random</syntaxhighlight> without worry.

You can make stuff dependent on the game mode. There are functions which return the game type, such as "<syntaxhighlight lang="lua" inline>Spring.Utilities.Gametype.is1v1()</syntaxhighlight>".<!-- The full list USED TO BE here: https://github.com/ZeroK-RTS/Zero-K/blob/master/LuaRules/Utilities/teamFunctions.lua#L74-->

An important thing is that <syntaxhighlight lang="lua" inline>#Spring.GetAllTeams()</syntaxhighlight> will return a wrong value due to fake technical teams and Gaia. Instead, use <syntaxhighlight lang="lua" inline>Spring.Utilities.GetTeamCount()</syntaxhighlight> to get the real number of teams.

== Examples ==

* [https://github.com/ZeroK-RTS/Zero-K/blob/master/LuaRules/Configs/StartBoxes/SpeedMetal.lua SpeedMetal] - the simplest layout, just two squares.
* [https://github.com/ZeroK-RTS/Zero-K/blob/master/LuaRules/Configs/StartBoxes/DeltaSiegeDry.lua DSD] - huge polygons, but otherwise very simple.
* [https://github.com/ZeroK-RTS/Zero-K/blob/master/LuaRules/Configs/StartBoxes/Sever%201.lua#L343 Sever] - shows an example of smaller boxes for 1v1 and larger for teams.
* [https://github.com/ZeroK-RTS/Zero-K/blob/master/LuaRules/Configs/StartBoxes/Isle%20of%20Grief%200.2.lua Isle of Grief] - shows a smart approach, one of the boxes is not defined rigidly but is a mirror of the other (only really feasible for rough boxes or perfectly symmetrical maps).
* [https://github.com/ZeroK-RTS/Zero-K/blob/master/LuaRules/Configs/StartBoxes/Aum_1.1.lua Aum] - another small trick, this time 5-way radial symmetry.
* [https://github.com/ZeroK-RTS/Zero-K/blob/master/LuaRules/Configs/StartBoxes/Throne%20v1.lua Throne] - multiple boxes defined, with a system to pick some of them based on how many teams there are.
* [https://github.com/ZeroK-RTS/Zero-K/blob/master/LuaRules/Configs/StartBoxes/Speed_Ball_10x10.lua Speedball] - shows boxes that are generated completely algorithmically.
* [https://github.com/ZeroK-RTS/Zero-K/blob/master/LuaRules/Configs/StartBoxes/Mearth_v4.lua#L6 Middle-Earth] - interesting team names.
* [https://github.com/ZeroK-RTS/Zero-K/blob/master/LuaRules/Configs/StartBoxes/Adansonia%20v2.lua Adansonia v2] - shows synchronizing boxes across map versions.
* [https://github.com/ZeroK-RTS/Zero-K/blob/master/LuaRules/Configs/StartBoxes/duck.lua Duck] - boxless config for silly maps where everybody can start anywhere.

[[Category:Development]]{{Navbox manual}}