How to make levels for Dungeon Crawl Stone Soup
-----------------------------------------------

Part IV:   TRIGGERABLES
           ============

Contents:  A. Introduction
           B. Sample syntax
           C. Examples of usage
           D. Convenience functions
           E. List of triggerers
           F. Master and slaves

This document describes the usage of Triggerables, a modular, extensible and
highly flexible Lua marker system used for making vaults. For more general
syntax and other advanced Lua topics, see introduction.txt, syntax.txt and
advanced.txt.

A.   Introduction
=================

Triggerables are an event-driven framework that can be used to further randomise
Dungeon Crawl Stone Soup maps, specifically at runtime. They can be used in
every-day minivaults, portal vaults, branch endings and more.

You've probably already used Triggerables in vaults, or seen them in action:
FogMachines are a randomised Triggerable, while many altar and trap vaults use
Triggerables to take some action when the player comes into view or steps on a
specific square. These often-used Triggerables may be wrapped in convenience
functions (see section D).

However, Triggerables can be combined with pre-defined Lua functions to achieve
extremely complicated game mechanics: in the "Collapsing Caverns" Volcano vault,
they are used to randomly close cave entrances, while in the "Overflow" Volcano
vault, they are used to increase and decrease the amount of lava present.

Triggerables are usually only limited by the amount of triggers (see
the list in section E), and Lua wrappers available. As these are constantly
increasing, you are really only limited by imagination and vault design ethics.

Sections B and C cover customised Triggerables (using examples from the Volcano
portal vaults), while section D covers convenience functions (using examples
from Branch ends).

B.   Sample syntax
==================

Customised Triggerers usually use the non-abstracted TriggerableFunction
mechanic. Consider this (trimmed) example from the Volcano portal vault (see
dat/volcano.des for the full vault):

-----------------------------

{{
-- Function in .des file prelude:
function callback.collapse_doorways (data, triggerable, triggerer, marker, ev)
  if triggerer.type ~= "turn" or triggerer.sub_type ~= "countdown" then
    return
  end

  [Doorway collapse code]

  -- Don't collapse same doorway twice.
  triggerable:remove(marker)
end
}}

{{
-- Code in the actual vault:
local collapse_marker = TriggerableFunction:new (
  {
    func="callback.collapse_doorways",
    repeated=true,
    props = {
      -- Only collapse one doorway at a time, randomly.
      single_random_slave="true"
    }
  }
)

collapse_marker:add_triggerer(DgnTriggerer:new {
  type="turn",
  delay_min=50,
  delay_max=200
})

}}

-----------------------------

As you can see, a TriggerableFunction consists of three parts: firstly, the
function that is to be triggered, which is provided five parameters:

  * data, a pre-defined Lua table which can be used for persistent data storage.
  * triggerable, the instance of the Triggerable that is triggering the
        function.
  * triggerer, the instance of the DgnTriggerer that has fired
  * marker, the marker object
  * ev, the event object

In most instances, the used parameters are "data", "triggerer" and "marker". The
first of these allows for the storage of any function-required data persistently
(such as the number of doorways already collapsed, the number of doorways left
to collapse, etc).

Note that the function to be triggered must be defined as a global
function in the .des file prelude (or in a .lua file in dat/dlua that
is required() by the .des file prelude), and that the function must be
specified by its global name.

"Triggerer" is regularly used in randomised functions to determine whether or
not the function is actually being fired. For example, if the Triggerer is not
of the "turns" type and "countdown" subtype; see the WarningMachines in
dat/dlua/lm_fog.lua for examples of functions being triggered randomly, and
being triggered a certain number of turns before a FogMachine is fired).

Finally, "marker" is usually used to determine the position of the Triggerable
by colling the "marker:pos()" function.

-----------------------------

The second part of the TriggerableFunction is the actual marker. In this case,
it is an instance of TriggerableFunction, called via TriggerableFunction:new.
This requires the "func" parameter, the name of the function that is to be
called.

It also optionally takes the following parameters: "repeated" which defaults to
'false': a non-repeated Triggerable will be removed after its first firing, and
will not be subsequently fired.

"props". A table consisting of one or more properties. In this instance takes
the "single_random_slave" parameter, which is linked into Master and Slave
mechanics (see Section F).

"data". A table consisting of data used by the function. This defaults to a
blank table, but can be specified with on creation of the marker. (See the
"Overflow" Volcano map in dat/volcano.des).

-----------------------------

The third and final part of the Triggerable is the actual trigger itself: this
is an instance of DgnTriggerer, and is added to the marker with the
"add_triggerer" function. See section E, "List of triggerers" for more
information.

-----------------------------

In our example, all of this combined creates a Triggerable which does the
following (ignoring the master/slave mechanics):

1. Randomly every "50" and "200" "turns"[1]
2. Pick a random slave
3. Trigger the function "collapse_doorways" at the slave
4. Remove the triggerer from that slave.

This is repeated until all of the triggerers have been removed, or the player
leaves the level.

[1]: "Turns" are a misnomer. The countdown operates off the value of ev:ticks(),
     a value which may be, but is not always, "10" for every turn. In practise,
     for randomised functions, you can times your values by 10 to roughly get
     a "turns" value: therefore, "50" ~= every 5 turns, "200" ~= every 20 turns.

The following section will provide some annotated examples of customised
TriggerableFunctions.

C. Examples of usage
====================

These vaults were taken in whole from the crawl code repository, and several
have been updated or removed since their original inclusion. Please see the
referenced files for the current version.

Annotations are marked as "** <text of annotation>".

-----------------------------

From dat/volcano.des:

{{
function callback.convert_lava (data, triggerable, triggerer, marker, ev)
  ** This piece of code ensures that the function is only triggered at the
  ** end of the countdown.
  if triggerer.type ~= "turn" or triggerer.sub_type ~= "countdown" then
    return
  end

  ** Here, values stored in the persistent table are altered.
  data.lava_phase = data.lava_phase + 1
  local lp = data.lava_phase
  local my_slaves = {}

  ** This code converts a square either from floor to lava, or from lava to
  ** floor.
  -- So we don't have to duplicate code too much.
  local function convert_slaves_to_lava (mslaves, opposite)
   local yp = dgn.point(you.pos())
    for _, pos in ipairs(mslaves) do
      if pos ~= yp then
        if opposite then
          dgn.terrain_changed(pos.x, pos.y, "floor", false, false, false)
        else
          dgn.terrain_changed(pos.x, pos.y, "lava", false, false, false)
        end
      end
    end
  end

  ** The use of slaves in this function is slightly different to the normal
  ** slaved Triggerables. Instead, we access the slave fetching functions
  ** directly in the code.
  if lp == 1 then
    crawl.mpr("The ground shudders ominously.", "warning")
  elseif lp == 2 then
    my_slaves = dgn.find_marker_positions_by_prop("lava_phase", 2)
    crawl.mpr("In the distance, the volano explodes with a roar! Lava spreads "
               .. "onto the path.", "warning")
    convert_slaves_to_lava(my_slaves)
  elseif lp == 3 then
    crawl.mpr("The air is thick with the scent of sulphur.", "warning")
  elseif lp == 4 then
    my_slaves = dgn.find_marker_positions_by_prop("lava_phase", 4)
    crawl.mpr("There is another distant roar. More lava overflows!", "warning")
    convert_slaves_to_lava(my_slaves)
  elseif lp == 5 then
    crawl.mpr("The ground moves violently!", "warning")
  elseif lp == 6 then
    my_slaves = dgn.find_marker_positions_by_prop("lava_phase", 6)
    crawl.mpr("The volcano erupts again! A thin layer of lava overflows to " ..
              "fill the cavern.", "warning")
    convert_slaves_to_lava(my_slaves)
  elseif lp == 7 then
    my_slaves = dgn.find_marker_positions_by_prop("lava_phase", 6)
    crawl.mpr("The ground shudders. Some of the lava has hardened enough to " ..
              "walk over!", "warning")
    convert_slaves_to_lava(my_slaves, true)
  end
end
}}

NAME:       volcano_overflow
WEIGHT:     10
ORIENT:     encompass
TAGS:       volcano no_item_gen no_monster_gen no_rotate
MONS:       nothing, nothing, nothing
{{

** The function takes five parameters, as noted, though only acts on two.

** This sets up the various slaves, using a portal descriptor with the
** lava_phase being parameter used to locate them.

-- So we know what to convert.
lua_marker("1", portal_desc { lava_phase=2 })
lua_marker("2", portal_desc { lava_phase=4 })
lua_marker("3", portal_desc { lava_phase=6 })

** The marker for the TriggerableFunction, and the initial setup of the data
** table.
-- And finally, let's convert it
local sink_marker = TriggerableFunction:new {
  func = "callback.convert_lava",
  repeated = true,
  data = {lava_phase=0}
}

** The triggerer is randomly every 5 to 20 turns.
sink_marker:add_triggerer(DgnTriggerer:new {
  type="turn",
  delay_min=50,
  delay_max=200, })

** While we need the marker on the map, it doesn't actually use or manipulate
** anything at its location, hence it's inclusion outside of the bounds of the
** map. This could easily be applied to any permanent feature included on the
** map, such as the "<" or "A" symbols.
lua_marker("M", sink_marker)
}}
SUBST:      M = c
NSUBST:     123 = 8:d / 8:e / 8:f / 8:g / 8:h / *:.
:           volcano_setup(_G)
MAP
                xxxx         xxx xxx                   xxx
        xxxxx  xx33xxx     xxx3xxx3xxxx xxxxx xxx     xx3xx
       xx333xxxx32233xxx xxx3323332333xxxx33xxx3xxx xxx323xx
     xxx321133332112233xxx332211221121333322333233xxx332123xx
   xxx3321l122221ll11133333311ll111l111222212211223332211123xx
 xxx3321llll1111llllll111111lllllllllll11111111111222111123xx
xx3321llllllllllllllllllllllllllllllllllll11233321111ll123xx
 xx3321lllllllllllllllllllllllllllllllllll123xxx3321lll123xx
  xxx321lllllllllllllllllllllllllllllllll123xxAxxx321lll123xx
    xx321lllllllllllllllll111lllllllllll123xx<...xx3211ll123xx
     xx321lll11llllllll122333221lllllllll123xxx...xx321lll123x
      x321ll1221llllll1223xxx3211llllllll11233x....3321llll13xx
    xxx321l133321llll1233xx xx3221llllllll123xx...xx321ll1123xx
   xx3321133xxx33211123xxx   xx3321llll11233333.xxx322111233xx
   x332233xxx xxx33233xx      xxx332111233xxxxxxx xx332233xxx
   xxx33xxx     xxx3xxx    M    xxx33233xxx        xxx33xxx
     xxxx         xxx             xxx3xxx            xxxx
                                    xxx
ENDMAP

-----------------------------

From dat/float.des

{{
function callback.skele_death (data, triggerable, triggerer, marker, ev)
  data.skele_number = data.skele_number + 1
  ** However, as this is a monster_dies function, we don't need to worry about
  ** it being triggered erroneously.

  ** And again, using the persistent data table to store the amount of skeletal
  ** warriors that have been destroyed.
  -- Only 7 skeles!
  if data.skele_number > 7 then
    return
  end

  ** Like the overflow vault from volcano.des, this directly accesses the
  ** network of slaves in order to find out which section of wall should be
  ** replaced.
  local function get_slave (slavenum)
    local myslaves = dgn.find_marker_positions_by_prop("skele_slave", slavenum)
    return myslaves[1]
  end

  local wall_pos = get_slave(data.skele_number)
  if wall_pos == nil then
    crawl.mpr("Couldn't find a slave!")
  end

  dgn.terrain_changed(wall_pos.x, wall_pos.y, "floor", false, false, false)

  if you.see_cell(wall_pos.x, wall_pos.y) then
    crawl.mpr("As the champion dies, a metal wall slides away!")
  else
    crawl.mpr("As the champion dies, you hear a distant grinding noise.")
  end
end

}}

NAME:   ancient_champions_mu
DEPTH:  D:15-26, Vault, Crypt
ORIENT: float
TAGS:   no_item_gen no_monster_gen
KFEAT:  ABCDEFG = metal_wall
** This vault uses named monsters to differentiate on the monster_dies trigger.
KMONS:  1 = col:gold skeletal warrior name:ancient_champion name_replace \
        spells:iron_shot;.;haste;pain;.;. actual_spells \
        ; plate mail ego:fire_resistance | plate mail ego:cold_resistance . \
        great sword ego:pain | great sword ego:draining | great sword \
        ego:flaming | w:3 triple sword ego:vorpal
KMONS:  2 = col:gold skeletal warrior name:ancient_champion name_replace \
        spells:bolt_of_draining;.;haste;throw_frost;.;. actual_spells \
        ; plate mail ego:fire_resistance | plate mail ego:cold_resistance . \
        great mace ego:vorpal | great mace ego:draining
KMONS:  3 = col:gold skeletal warrior name:ancient_champion name_replace \
        spells:venom_bolt;.;haste;haunt;.;. actual_spells \
        ; plate mail ego:fire_resistance | plate mail ego:cold_resistance . \
        battleaxe ego:vorpal | battleaxe ego:pain | \
        w:3 executioner's axe ego:vorpal
KMONS:  4 = col:gold skeletal warrior name:ancient_champion name_replace \
        spells:iskenderun's_mystic_blast;slow;haste;.;.;. actual_spells \
        ; plate mail ego:fire_resistance | plate mail ego:cold_resistance . \
        great sword ego:pain | great sword ego:draining | great sword \
        ego:flaming | battleaxe ego:vorpal | battleaxe ego:pain | \
        triple sword ego:vorpal | executioner's axe ego:vorpal
SHUFFLE: 123
KPROP:  ]v.1234+ABCDEFG!n$wr|" = no_rtele_into
KITEM:  w = weapon good_item
KITEM:  r = armour good_item
NSUBST: $ = 1:w / 1:r / 4:| / *:$
COLOUR: " = yellow
KFEAT:  " = .

{{

** In this vault, killing one of the name skeletal warriors causes part of the
** wall to slide back. These sections of wall have to be individually marker as
** such.
-- First off, slave marker magic.
lua_marker("A", portal_desc { skele_slave=1 })
lua_marker("B", portal_desc { skele_slave=2 })
lua_marker("C", portal_desc { skele_slave=3 })
lua_marker("D", portal_desc { skele_slave=4 })
lua_marker("E", portal_desc { skele_slave=5 })
lua_marker("F", portal_desc { skele_slave=6 })
lua_marker("G", portal_desc { skele_slave=7 })

** Again, taking five parameters.

local skele_death_marker = TriggerableFunction:new {
  func="callback.skele_death",
  repeated=true,
  data={skele_number=0} }

** This uses the "monster_dies" type of triggerer, and links it in to the
** changed description of the skeletal warriors.
skele_death_marker:add_triggerer(DgnTriggerer:new {
  type="monster_dies",
  target="ancient champion" })

** Again, like the Overflow vault, the marker in question doesn't act upon
** anything at its location; assigning it to all of the skeletal warriors
** would cause confusion, and placing it off the map would be impossible as
** this is not an encompass vault; therefore, it is linked to a solid feature.
lua_marker("]", skele_death_marker)
}}

MAP
vvvvvvvvvvvvvvvvvvv
v..".1v.."..v.."..v
v.""".v.""".v.""".v
v"""""C"""""B"""""v
v.""".v.""".v.""".v
v.."..v..".3v..".2v
vvvDvvvvvvvvvvvAvvv
v..".2v$$$$$v.."..v
v.""".v$$$$$v.""".v
v"""""v$$.$$v"""""v
v.""".v$$.$$v.""".v
v.."..v$...$v1."..v
vvvEvvvvvGvvvvv+vvv
v3."..v.."..v.."..v
v.""".v.""".v.""".v
v"""""F"""""v""]""v
v.""".v.""".v.""".v
v.."..v4."..v.."..v
vvvvvvvvvvvvvvvvvvv
ENDMAP

D. Convenience functions
========================

Previously, we have discussed completely customised Triggerables, using the
TriggerableFunction marker. There also exist a large variety of other markers
and convenience functions which use Triggerables as a base.

Markers which use Triggerables as a base include FogMachines, MonsterOnTrigger,
feat_change_change_flags, item_pickup_change_flags, and so on. These are
documented in their own individual files.

Currently, convenience functions for Triggerables include:

  * message_at_spot, which can be used to trigger a single or repeated message
      whenever the player crosses or reaches a certain point.
  * function_at_spot, as above, but accepts a function and data parameter
      instead of message and channel.

E.    List of triggerers
========================

This list taken from dat/dlua/lm_trig.lua, listing the different "type"
parameters that an instance of DgnTriggerer may accept, and the required
parameters for each.

   * monster_dies: Waits for a monster to die. Needs the parameter
         "target", who's value is the name of the monster who's death
         we're wating for. Doesn't matter where the triggerable/marker
         is placed.
   * feat_change: Waits for a cell's feature to change. Accepts the
         optional parameter "target", which if set delays the trigger
         until the feature the cell turns into contains the target as a
         substring. The triggerable/marker must be placed on top of the
         cell who's feature you wish to monitor.
   * item_moved: Wait for an item to move from one cell to another.
        Needs the parameter "target", who's value is the name of the
        item that is being tracked, or which can be "auto", in which
        case it will pick the item placed by the vault. The
        triggerable/marker must be placed on top of the cell containing
        the item.
   * item_pickup: Wait for an item to be picked up. Needs the parameter
        "target", who's value is the name of the item that is being tracked,
        or which can be "auto", in which case it will pick the item placed
        by the vault. The triggerable/marker must be placed on top of the
        cell containing the item. Automatically takes care of the item
        moving from one square to another without being picked up.
   * player_move: Wait for the player to move to a cell. The
        triggerable/marker must be placed on top of cell in question.
   * player_los: Wait for the player to come into LOS of a cell, which
        must contain a notable feature. The triggerable/marker must be
        placed on top of cell in question.
   * turn: Called once for each player turn that passes. Optionally accepts a
        "delay_min", "delay_max" or "delay" parameters, in which case a
        countdown is performed.
   * entered_level: Called when player enters the level, after all level
        setup code has completed.

F.     Master and slaves
========================

Multiple Triggerables can be combined together in a master/slave setup. There
are multiple methods of doing this. The simplest is to provide a
"master_name" parameter to the main marker, and then provide "slave_to" at all
of the individual slave markers, setting the same value for each.

When a Triggerable is fired and it has a "master_name" property, it will execute
at each of the slave locations as defined above, unless the master has the
parameter "single_random_slave" (set to anything but empty), in which case it
will randomly chose one slave and execute there. Further, the master marker may
be slaved to itself in order to have execution occur there.

Triggerables that depend on position (such as player_move) will only fire when
the player moves over the master marker. For them to fire at either slave or
master, provide the "listen_to_slaves" property. Finally, to have only the slave
that fired be executed, provide the "only_at_slave" parameter.

-----------------------------

An example from dat/hells.des, using the MonsterOnTriggerer marker, a subset of
Triggerables, and master/slave mechanics:

MARKER:  1 = lua:monster_on_death { \
            death_monster="Dispater", new_monster="generate_awake iron golem", \
            message_seen="The iron statue comes to life!", \
            message_unseen="You hear a grinding sound.", \
            master_name="dispater" \
         }
MARKER:  o = lua:props_marker { \
            veto_fragmentation="veto", veto_disintegrate="veto", \
            slaved_to="dispater" \
         }

-----------------------------

If you have any comments, questions, or issues with Triggerables, your best bet
would be #crawl-dev on Libera IRC.