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[TOC] ¶

Some initial help for creating a scenario, either for creating a complete campaign or as a standalone scneario. If you have reached the end of this tutorial you will have some basic knowledge on how to create a scenario. We can't provide a full explanation of the Lua language, nor all the possibilities of the Lua interface that widelands provides in this tutorial. Please also note that there are sometimes different ways to archive the same thing. ¶

What you should know before reading on: ¶

* [First steps for a scenario]( ¶
* Make sure to use a plain text editor when writing scripts, e.g. [notepad++](, [Geany]( or [dig through wikipedia articles about text editors]( ¶
* You may also take a look in the scripting files of the implemented campaigns, which you can find in the data directory of your widelands installation. Look into the folder data/campaigns. This article follows the same structure of filenames. ¶

To follow this example, create an empty map with only one player set at position 0,0 . To find this position watch the values at the bottom right in the editor. This values represents: (x position, y position, height). Make sure you have set the tribe 'Empire' in the menu 'Set Player'. ¶

## init.lua ¶

You have read that the file `your_map/scripting/init.lua` is the main entry for your scenario. So this file is the starting point and should contain necessary global settings. This file contains usually different parts: ¶

### Including some helpers ¶

~~~~ ¶
include "scripting/coroutine.lua" ¶
include "scripting/messages.lua" ¶
include "scripting/ui.lua" ¶
include "scripting/richtext.lua" ¶
~~~~ ¶

The files which get included here contain functions which you may need in your project. E.g. the file _'coroutine.lua'_ contain a function `sleep(time)`. Those files (and their functions) are described in [Auxiliary Scripts]( Please take a look at the includes above and look into the corresponding auxiliary scripts documentation to get knowledge about their functions. Don't worry if you don't understand that much at the moment. Later on we will see how to use them. ¶

### Global variables ¶

In this part of the file _'init.lua'_ we define variables which we want to
bhave available each time. That's why they are called 'global' variables. This global variables are shortcuts and prevent writing each time the same: ¶

~~~~ ¶
plr = wl.Game().players[1] ¶
map = wl.Game().map ¶
plr_sf = map.player_slots[1].starting_field ¶
~~~~ ¶

What this code does: ¶

* `plr = wl.Game().players[1]`: This reads the first defined player of the map (the one you have set) and assign it to the variable 'plr'. If you have set more players to the map, they can be accessed by increasing the value in the brackets, so `.players[2]` is the second player. ¶
* `map = wl.Game().map`: The variable 'map' gives you now access to many properties of the map itself, e.g. to the function `get_field()` in [Map]( This will be the most used function in your scenario. ¶
* `plr_sf = map.player_slots[1].starting_field`: You have set a player in the map editor on a field, so this assigns this field to the global variable 'plr_sf'. Note that we use here already the variable 'map' which we have defined one line above. Also note that there is a point between 'map', 'player_slots' and 'starting_field'. I tell you later why this is important. ¶

### Including the script to load starting conditions ¶

Now we are ready with initialization and can work on to get the story alive. To split of initialization and other stuff, we include another file in the last line in our `init.lua` : ¶

~~~~ ¶
include "map:scripting/starting_conditions.lua" ¶
~~~~ ¶

The file _'startin
dg_conditions.lua'_ will contain initial settings for the scenario. The include at the end of the file _'init.lua'_ makes sure all other initialization is done and all defined global variables are available in each further included file. ¶

## starting_conditions.lua ¶

The map you have created is empty by default. You have set a player, but no buildings at all. It is our part to place buildings. ¶

### Place buildings ¶

First we place the headquarters for player 1. Do you remember you have set the global variables `plr` and `plr_sf`? Here we use them: ¶

~~~~ ¶
local hq = plr:place_building("empire_headquarters", plr_sf, false, true) ¶
~~~~ ¶

We call the function [place_building()](/docs/wl/autogen_wl_bases/#wl.bases.PlayerBase.place_building) with the needed arguments (the entries in the brackets). The first argument for the function is a string (enclosed in double quotation marks). You could find the correct string in the corresponding init.lua of the building in the subfolders of _'data/tribes/buildings/'_. You need the string of the _'name'_ attribute here. ¶

The above function returns a reference to the created buildings. In this example this is stored in the __local__ variable `hq`. ¶

__Importand remark about local:__ Whenever you assign variables with values, you should do it this way: `local name_of_variable = value`. The keyword _local_ makes sure that this variable is only valid in this scope (file or function). The only exception: If you really know that you will use this variable elsewhere, you can omit the keyword `local`. But in this case you should give the variable a name which is absolutely clear! ¶

Note the colon between `plr` and the functions name. Do you remember that we had already a point as a separator? Time for a small explanation about the difference between point and colon: ¶

Consider to have an object like a car. This car has a property: color. But this car has also some functions: drive_straight(), drive_left(), drive_right(). If you want to get the color, you want to access the property: `clr = car.color.` If you want to drive the car you need to call the functions: `car:drive_straight(100 meter)`. Do you see the difference? Accessing a property needs a point, calling a function needs a colon! If you go through the documentation you may notice that some entries have brackets, and others not. The entries with brackets are functions, other are properties. Examples: ¶

* Properties (can be accessed through a point): [](, [Map.width](/docs/wl/autogen_wl_map/
* Functions (must be called with a colon): [Player:sees_field(f)](, [Map.get_Field(x,y)](/docs/wl/autogen_wl_map/ ¶

Now its time for a first test. Run: ¶

~~~~ ¶
./widelands --scenario=/full/path/to/the/map.wmf ¶
~~~~ ¶

You should see the placed headquarters after loading is complete. Look at the stock... the headquarters is empty, no wares and workers are in it. We should change that. ¶

### Fill buildings ¶

The function [place_building()]( returns a reference to the created building. We have assigned this reference to the local variable `hq`. ¶

Now we can use this variable and the function [set_wares()]( to fill the building: ¶

~~~~ ¶
hq:set_wares("log",10) ¶
hq:set_wares("planks",10) ¶
hq:set_wares("granite",10) ¶
~~~~ ¶

Because setting wares is a common task, there is a shortcut by passing a table to set_wares(): ¶

~~~~ ¶
hq:set_wares({ ¶
log = 10, ¶
planks = 20, ¶
granite = 20, ¶
marble = 5, ¶
}) ¶
~~~~ ¶

Same goes for setting workers and soldiers: ¶

~~~~ ¶
hq:set_workers({ ¶
empire_builder = 5, ¶
empire_carpenter = 2, ¶
empire_lumberjack = 5, ¶
}) ¶

hq:set_soldiers({0,0,0,0}, 45) ¶
~~~~ ¶

Like with the buildings name you will find the right names for wares and workers in the corresponding _'init.lua'_ in the subfolders of _'data/tribes/'_. Add as many wares and workers as you like. After your'e done you should make a test run again. ¶

Now its time to crea
ete our main control script. It is usually called _'main_thread.lua'_ ¶

## main_thread.lua and texts.lua ¶

The file _'main_thread.lua'_ contains all the logic for the scenario. The file _'texts.lua'_ contains
all the xts for message boxtes that our scenario needs. This chapter explains the usage of this files. ¶

### Message boxes ¶

You may have seen that our scenarios have some message boxes to inform the player about the story. In our _'init.lua'_ we have included 'messages.lua'. This file contains convenient functions for messages. We are using [campaign_message_box()]( and add it to the new file _'main_thread.lua'_:

~~~~ ¶
campaign_message_box({title = "This is the title", body = p("Hi, this is my first scenario")}) ¶
~~~~ ¶

We give the function a table (enclosed with curly braces {}). The 'body' must be formatted with the richtext system,
soand we warape using the function ap() for p-taghis. See [richtext.lua]( for further formatting functions. ¶

The fi
ele _'main_thread.lua'_ must be loaded, so add an _include_ as last line in _'ini.lua'_: ¶
~~~~ ¶
... ¶
include "map:scripting/starting_conditions.lua" ¶
include "map:scripting/main_thread.lua" ¶
~~~~ ¶

Run a test.
The message box should be shown after loading has finished.

You may have more than one message box in your campaign. For better readability of your main script in _'main_thread.lua'_ it is ususally better to put the table(s) of text in an extra file. The built in campaigns have them usually in a file called _'texts.lua'_ which get included in the [
after including the blostarting_ck of your inditions.lua](/#including-the-script-tome-helpeoad-starting-conditions) or at the beginning of _'main_thread.lua'_. This will look then like: ¶

File _'texts.lua_': ¶

-- Store the table in the variable 'first_message'

first_message = { ¶
title = "This is the title", ¶
body = p("Hi, this is my first scenario")
} ¶
~~~~ ¶

File _'main_thread.lua'_: ¶
~~~~ ¶
-- Including tables of text ¶
include "map:scripting/texts.lua" ¶

campaign_message_box(first_message) ¶
~~~~ ¶

The first line
s in the above examples (beginning with two hyphens) is are comments. You should comment your code as musch as possible but not more than needed. When

ycould alstarto modify thie mes scenario thge fbollowingx, willby happelyin: ¶

g The pradditiogrnaml valookues ftor a filthe ctalbled in _'scripting/iniexts.lua'_: ¶
~~~~ ¶
-- Store the table
in the mvapriable d'firecsto_message' ¶
ry.st_message = { ¶
If title = "This preis then title",
lboady = p("Hi, t: ¶
his Readings _'my first scenit.lua'_ friom"), ¶
top to So= 1, ¶
all functiponsy of= includ1, ¶
} ¶
~~~~ ¶
ede fil[mes sand ge_box()](/docs/wl/autobagen_wl v_gariabme/#wles .garme .Ploadyedr. Thme lssast linge_box) include four file _'main_thr ead.xplua'_ snation. th

ise: will be

rePlad ¶
y Rearounding fwileth _'main_thre vad.lua'_es ofrom to_p to bottom. Heresx_ we ianclude _'textpos.lua'y_
Chand allge tablhes willdth be loadend. Thenight showf the message box.


### Triggering events - adding logic ¶

For now we have some basics, but we need some events to make the campaign alive. Such events are the most important things in campaigns. They offer functionality like: ¶

* Show message boxes when things happens ¶
* Running out of building material ¶
* The player has reached a specific point on the map ¶
* A specific building has been build ¶
* Add objectives a player has to solve ¶
* and so on ¶

Usually an event is combined with an objective, but we leave creating objectives for now and concentrate on programming an event. In this example we create an event if the player reaches a specific point on the map. There are two possibilities to get this work: ¶

* Checking the return value of the function [Player:sees_field()]( ¶
* Checking the property [Field.owner]( ¶

Both possibilities needs a field to work with. So the first thing is to get a field. Fields are part of the map and can be accessed through `wl.Game().map`. We have assigned this to the variable `map` in the [global variables section of init.lua](#global-variables). Now we use this variable and call the function [map:get_field(x,y)]( This function needs the x and y coordinates of the map, so add the following to _'main_thread-lua'_ below the call to campaign_message_box: ¶

~~~~ ¶
-- Get the field at position x=10, y=0 and store it in the variable 'field' ¶
local field = map:get_field(10,0) ¶
print("Field: ", field , "Owner: ", field.owner) ¶
~~~~ ¶

If you run the scenario the field
coordinates and the owner of that field (currently the value is 'nil') will be printed in the console. Note that the print statement is only executed after clicking "OK" in the message box. ¶

What we need further is a mechanism to check if the owner of that field changed. We need a loop that runs the same code over and over until the owner has changed. The problem with such loops is that they can't be run as a standalone loop in lua. This is where coroutines comes in. A coroutine is started with the
functiommand [run(name_of_function)]( ThWe function _run()_ needs a function, so we wrap the loop inside a function and call `run(name_of_function)` with the functions name as argument at the end of _'main_thread.lua'_. Replace the previous added code with this one, note the moved message box: ¶

~~~~ ¶
function check_field_owner() ¶
local field = map:get_field(10,0) ¶
while true do ¶
print("Field: ", field , "Owner: ", field.owner) ¶
sleep(1000) ¶
end ¶
end ¶

run(check_field_owner) ¶

campaign_message_box(first_message) ¶
~~~~ ¶

Run the scenario
. ¶

and loowk into thev console output. Aftery loading ise condmplete, the field coordinates and the field owner is printed ofut exactly one time. Then the message box appears. If you click on "OK" the print statement is further called every second. The important thing with this observation pis: ¶

The co
routine get called (`run(name_of_funtion)`) and executed, but the scoript runs further. All code after the call to `run()` will be executed also. In this case: The message box is shown ¶

The row `sleep(1000)` is __really__ important. If you forget that, this loop prevents every interaction between you and the program itself: ¶

* A player can't do anything else while the
lcoroputine is executed ¶
* The only way to stop it is to kill the whole program either by clicking on the 'X' of the window, or with your taskmanager ¶

Ok, now it's time for some magic: Run your scenario and explore into the direction of the field (to the right). As soon the field is owned by you, the output will change. Why is this magic? The variable _field_ is defined outside of the loop so it is initialized only once. One could think that the fields state (the owner in this case) is also only initialized once, but this is not the case. That is because the variable _field_ is a __reference__ to the field. Whenever this field
owner changes the changes are also reflected in the variable _field_! ¶

The loop created here will never end. We change that now by adding a condition to the loop.
AllYou wemay have seen in tohe dco ins toles comutput, thart the `_field.owner_ has changed to `Player(1)`. wWe have assithgned ou`player[1]` to the global variable `plr` (which we have setn [_'in [Git.lua'_](#global -variables](#), so we compare `field.owner` with our global- variables) `plr`. To check that the loop is really endet, we add also another message box: ¶
~~~~ ¶
function check_field_owner() ¶
local field = map:get_field(10,0) ¶
while field.owner ~= plr do ¶
sleep(1000) ¶
end ¶
{ {title = "Field fouwned", body = p("WThis field haveis now reachowned theby fimeld")} ) ¶
end ¶

run(check_field_owner) ¶
~~~~ ¶

cloop rundis now untionl `field.owner ~= plr` means:(= `field.owner __not equal__ plr`). Such a comparison returns either 'true' or 'false'. See also [Rational Operators]( for other types. For other types of loops see [Control structures]( ¶

As soon the message box appears, we can be sure that the loop has been ended. Now, as an exercise, try to add a new function plr_sees_field() and use [Player:sees_field()]( for the condition. You have to choose another field though, one which is outside the area the player sees, for testing purposes i have used field 15,10. Move also the table of the message box into the file _'texts.lua'_ and make the corresponding changes. Run the new function by adding an additional `run()` command. ¶

When running the scenario, you should see at least two message boxes popping up: One after the first loop has ended, and the new one after the second loop has ended. ¶

If you can't get it to work,
look[here ins the chapter [Solutions](#sadd-anolther-functions). ¶

Note that both loops will end (the message boxes appear) without any delay. That means both functions are running simultaneously. This is the magic of coroutines, when running the functions with the command `run(function)`. The function will be loaded and executed, but the program turns immediately back and executes the additional function of the second call to `run()`. ¶

There is one drawback with coroutines: If you save the game, the coroutines and the state of their variables are saved also. This means you can't run a game, save it, change the logic of a coroutine, and reload the saved game to check the new logic of the coroutine. The new logic will not be part of the loaded save game, because it uses the old logic. The only way to test the new logic is to start a new game. This makes working on scenarios a bit hard, especially for beginners. At the end of this article are [some tips for testing coroutines](#tips-for-testing-coroutines) ¶

### Conclusion ¶

If you have reached this point of this tutorial you have learned a lot. Here are the main things: ¶

* Split logic and texts und leave logic in _'main_thread.lua'_ whereas put texts in other files ¶
* Include each other file either from _'init.lua'_ or at the beginning of _'main_thread.lua'_ ¶
* Use always the keyword `local` when defining variables, except in _'init.lua'_ ¶
* Add events as functions and call them with `run(function)` ¶
* Don't forget to use `sleep()` in loops ¶
* To verify variables you can always add a `print()` statement ¶
* Changing logic of coroutines have only affect if you start a new game ¶

## Objectives and objectives.lua ¶

If you have played some of our scenarios you have seen that there are objectives a player has to fulfill. Let's add an objective and also some other stuff: ¶

1. If the field is seen by the player, scroll automatically to that field ¶
2. Show a message box to the player ¶
3. If the player clicks ok in the message box, scroll back to the previous location ¶
4. Add an objective saying that he should build a forester, a woodcutter and produce at least 5 logs ¶
5. Show a message box if the objective is done ¶

The related function to get wares in stock is: [Player:get_wares()]( But for now we implement the automatic scrolling. The used functions are part of [ui.lua]( which we have [included in ini.lua](#including-some-helpers) and are called _scroll_to_field()_ and _scroll_to_map_pixel()_. _scroll_to_field()_ returns the center pixels of the current view. We store this in the local variable `scroll_field` and use this variable to give it _scroll_to_map_pixel()_ later on: ¶

~~~~ ¶
function check_field() ¶
local field = map:get_field(15,0) ¶
while not plr:sees_field(field) do ¶
sleep(1000) ¶
end ¶
local scroll_field = scroll_to_field(field) ¶
campaign_message_box(field_reached) ¶
scroll_to_map_pixel(scroll_field) ¶
end ¶
~~~~ ¶

## Solutions

### Play with message box attributes ¶

~~~~ ¶
-- Store the table in the variable 'first_message' ¶
first_message = { ¶
title = "This is the title", ¶
body = p("Hi, this is my first scenario"), ¶
posx = 1, ¶
posy = 1, ¶
w = 200, ¶
h = 200, ¶
} ¶

### Add another function ¶

Does your solution look like this one? ¶
~~~~ ¶
-- Added function to check sees_field() ¶
function check_sees_field() ¶
local field = map:get_field(15,0) ¶
while plr:sees_field(field) ~= true do -- See below ¶
sleep(1000) ¶
end ¶
campaign_message_box(plr_sees_field) ¶
end ¶

run(check_field) ¶
-- Additional run() command ¶
run(check_sees_field) ¶
~~~~ ¶

The condition for the loop could also be written this way to improve readability: ¶
~~~~ ¶
while not plr:sees_field(field) do ¶
~~~~ ¶

## Tips for testing coroutines ¶

* scriptconsole F6 ¶
* dofile("filename") ¶
* commenting coroutines ¶