path: root/doc/lua_api.txt

Minetest Lua Modding API Reference 0.4.dev
==========================================
More information at http://c55.me/minetest/

Introduction
-------------
Content and functionality can be added to Minetest 0.4 by using Lua
scripting in run-time loaded mods.

A mod is a self-contained bunch of scripts, textures and other related
things that is loaded by and interfaces with Minetest.

Mods are contained and ran solely on the server side. Definitions and media
files are automatically transferred to the client.

If you see a deficiency in the API, feel free to attempt to add the
functionality in the engine and API. You can send such improvements as
source code patches to <celeron55@gmail.com>.

Programming in Lua
-------------------
If you have any difficulty in understanding this, please read:
  http://www.lua.org/pil/

Startup
--------
Mods are loaded during server startup from the mod load paths by running
the init.lua scripts.

Mod load path
-------------
Generic:
  $path_share/games/gameid/mods/
  $path_share/mods/gameid/
  $path_user/games/gameid/mods/
  $path_user/mods/gameid/ <-- User-installed mods
  $worldpath/worldmods/

In a run-in-place version (eg. the distributed windows version):
  minetest-0.4.x/games/gameid/mods/
  minetest-0.4.x/mods/gameid/ <-- User-installed mods
  minetest-0.4.x/worlds/worldname/worldmods/

On an installed version on linux:
  /usr/share/minetest/games/gameid/mods/
  ~/.minetest/mods/gameid/ <-- User-installed mods
  ~/.minetest/worlds/worldname/worldmods

Mod directory structure
------------------------
mods
|-- modname
|   |-- depends.txt
|   |-- init.lua
|   |-- textures
|   |   |-- modname_stuff.png
|   |   `-- modname_something_else.png
|   |-- sounds
|   |-- media
|   `-- <custom data>
`-- another

modname:
  The location of this directory can be fetched by using
  minetest.get_modpath(modname)

depends.txt:
  List of mods that have to be loaded before loading this mod.
  A single line contains a single modname.

init.lua:
  The main Lua script. Running this script should register everything it
  wants to register. Subsequent execution depends on minetest calling the
  registered callbacks.

  minetest.setting_get(name) and minetest.setting_getbool(name) can be used
  to read custom or existing settings at load time, if necessary.

textures, sounds, media:
  Media files (textures, sounds, whatever) that will be transferred to the
  client and will be available for use by the mod.

Naming convention for registered textual names
----------------------------------------------
Registered names should generally be in this format:
  "modname:<whatever>" (<whatever> can have characters a-zA-Z0-9_)

This is to prevent conflicting names from corrupting maps and is
enforced by the mod loader.

Example: mod "experimental", ideal item/node/entity name "tnt":
         -> the name should be "experimental:tnt".

Enforcement can be overridden by prefixing the name with ":". This can
be used for overriding the registrations of some other mod.

Example: Any mod can redefine experimental:tnt by using the name
         ":experimental:tnt" when registering it.
(also that mod is required to have "experimental" as a dependency)

The ":" prefix can also be used for maintaining backwards compatibility.

Aliases
-------
Aliases can be added by using minetest.register_alias(name, convert_to)

This will make Minetest to convert things called name to things called
convert_to.

This can be used for maintaining backwards compatibility.

This can be also used for setting quick access names for things, eg. if
you have an item called epiclylongmodname:stuff, you could do
  minetest.register_alias("stuff", "epiclylongmodname:stuff")
and be able to use "/giveme stuff".

Textures
--------
Mods should generally prefix their textures with modname_, eg. given
the mod name "foomod", a texture could be called
  "foomod_foothing.png"

Textures are referred to by their complete name, or alternatively by
stripping out the file extension:
  eg. foomod_foothing.png
  eg. foomod_foothing

Sounds
-------
Only OGG files are supported.

For positional playing of sounds, only single-channel (mono) files are
supported. Otherwise OpenAL will play them non-positionally.

Mods should generally prefix their sounds with modname_, eg. given
the mod name "foomod", a sound could be called
  "foomod_foosound.ogg"

Sounds are referred to by their name with a dot, a single digit and the
file extension stripped out.  When a sound is played, the actual sound file
is chosen randomly from the matching sounds.

When playing the sound "foomod_foosound", the sound is chosen randomly
from the available ones of the following files:
  foomod_foosound.ogg
  foomod_foosound.0.ogg
  foomod_foosound.1.ogg
  ...
  foomod_foosound.9.ogg

Examples of sound parameter tables:
-- Play locationless on all clients
{
	gain = 1.0, -- default
}
-- Play locationless to a player
{
	to_player = name,
	gain = 1.0, -- default
}
-- Play in a location
{
	pos = {x=1,y=2,z=3},
	gain = 1.0, -- default
	max_hear_distance = 32, -- default
}
-- Play connected to an object, looped
{
    object = <an ObjectRef>,
	gain = 1.0, -- default
	max_hear_distance = 32, -- default
    loop = true, -- only sounds connected to objects can be looped
}

Representations of simple things
--------------------------------
MapNode representation:
  {name="name", param1=num, param2=num}

MapNodes do not directly have any other data associated with them.
If you want to access the definition of the node, you access
  minetest.registered_nodes[node.name]

param1 and param2 are 8 bit and 4 bit integers, respectively. They
are reserved for certain automated functions. If you don't use these
functions, you can use them to store arbitrary values.

param1 is reserved for the engine when:
  paramtype != "none"
param2 is reserved for the engine when any of these are used:
  liquidtype == "flowing"
  drawtype == "flowingliquid"
  drawtype == "torchlike"
  drawtype == "signlike"

Position/vector:
  {x=num, y=num, z=num}
Currently the API does not provide any helper functions for addition,
subtraction and whatever; you can define those that you need yourself.

stackstring/itemstring: A stack of items in serialized format.
eg. 'default:dirt 5'
eg. 'default:pick_wood 21323'
eg. 'default:apple'

item: A stack of items in Lua table format.
eg. {name="default:dirt", count=5, wear=0, metadata=""} 
    ^ 5 dirt nodes
eg. {name="default:pick_wood", count=1, wear=21323, metadata=""}
    ^ a wooden pick about 1/3 weared out
eg. {name="default:apple", count=1, wear=0, metadata=""}
    ^ an apple.

Any time an item must be passed to a function, it can be an
ItemStack (see below), an itemstring or a table in the above format.

SimpleSoundSpec:
eg. ""
eg. "default_place_node"
eg. {}
eg. {name="default_place_node"}
eg. {name="default_place_node", gain=1.0}

Items
------
Node (register_node):
  A node from the world
Tool (register_tool):
  A tool/weapon that can dig and damage things according to tool_capabilities
Craftitem (register_craftitem):
  A miscellaneous item

Groups
-------
In a number of places, there is a group table. Groups define the
properties of a thing (item, node, armor of entity, capabilities of
tool) in such a way that the engine and other mods can can interact with
the thing without actually knowing what the thing is.

Usage:
- Groups are stored in a table, having the group names with keys and the
  group ratings as values. For example:
    groups = {crumbly=3, soil=1}
    ^ Default dirt (soil group actually currently not defined; TODO)
    groups = {crumbly=2, soil=1, level=2, outerspace=1}
    ^ A more special dirt-kind of thing
- Groups always have a rating associated with them. If there is no
  useful meaning for a rating for an enabled group, it shall be 1.
- When not defined, the rating of a group defaults to 0. Thus when you
  read groups, you must interpret nil and 0 as the same value, 0.

Groups of items
----------------
Groups of items can define what kind of an item it is (eg. wool).

Groups of nodes
----------------
In addition to the general item things, groups are used to define whether
a node is destroyable and how long it takes to destroy by a tool.

Groups of entities
-------------------
For entities, groups are, as of now, used only for calculating damage.

object.get_armor_groups() -> a group-rating table (eg. {fleshy=3})
object.set_armor_groups({level=2, fleshy=2, cracky=2})

Groups of tools
----------------
Groups in tools define which groups of nodes and entities they are
effective towards.

Groups in crafting recipes
---------------------------
- Not implemented yet. (TODO)
- Will probably look like this:
{
    output = 'food:meat_soup_raw',
    recipe = {
        {'group:meat'},
        {'group:water'},
        {'group:bowl'},
    },
	preserve = {'group:bowl'},
}

Special groups
---------------
- immortal: Disables the group damage system for an entity
- level: Can be used to give an additional sense of progression in the game.
  - A larger level will cause eg. a weapon of a lower level make much less
    damage, and get weared out much faster, or not be able to get drops
	from destroyed nodes.
  - 0 is something that is directly accessible at the start of gameplay
  - There is no upper limit
- dig_immediate: (player can always pick up node without tool wear)
  - 2: node is removed without tool wear after 0.5 seconds or so
       (rail, sign)
  - 3: node is removed without tool wear immediately (torch)

Known damage and digging time defining groups
----------------------------------------------
Valid ratings for these are 0, 1, 2 and 3, unless otherwise stated.
- crumbly: dirt, sand
- cracky: tough but crackable stuff like stone.
- snappy: something that can be cut using fine tools; eg. leaves, small
          plants, wire, sheets of metal
- choppy: something that can be cut using force; eg. trees, wooden planks
- fleshy: Living things like animals and the player. This could imply
          some blood effects when hitting.
- explody: Especially prone to explosions
- oddly_breakable_by_hand:
   Can be added to nodes that shouldn't logically be breakable by the
   hand but are. Somewhat similar to dig_immediate, but times are more
   like {[1]=3.50,[2]=2.00,[3]=0.70} and this does not override the
   speed of a tool if the tool can dig at a larger speed than this
   suggests for the hand.

Examples of custom groups
--------------------------
Item groups are often used for defining, well, //groups of items//.
- meat: any meat-kind of a thing (rating might define the size or healing
  ability or be irrelevant - it is not defined as of yet)
- eatable: anything that can be eaten. Rating might define HP gain in half
  hearts.
- flammable: can be set on fire. Rating might define the intensity of the
  fire, affecting eg. the speed of the spreading of an open fire.
- wool: any wool (any origin, any color)
- metal: any metal
- weapon: any weapon
- heavy: anything considerably heavy

Digging time calculation specifics
-----------------------------------
Groups such as **crumbly**, **cracky** and **snappy** are used for this
purpose. Rating is 1, 2 or 3. A higher rating for such a group implies
faster digging time.

The **level** group is used to limit the toughness of nodes a tool can dig
and to scale the digging times / damage to a greater extent.

^ PLEASE DO UNDERSTAND THIS, otherwise you cannot use the system to it's
  full potential.

Tools define their properties by a list of parameters for groups. They
cannot dig other groups; thus it is important to use a standard bunch of
groups to enable interaction with tools.

**Tools define:**
  * Full punch interval
  * Maximum drop level
  * For an arbitrary list of groups:
    * Uses (until the tool breaks)
    * Maximum level (usually 0, 1, 2 or 3)
    * Digging times

**Full punch interval**:
When used as a weapon, the tool will do full damage if this time is spent
between punches. If eg. half the time is spent, the tool will do half
damage.

**Maximum drop level**
Suggests the maximum level of node, when dug with the tool, that will drop
it's useful item. (eg. iron ore to drop a lump of iron).
- This is not automated; it is the responsibility of the node definition
  to implement this

**Uses**
Determines how many uses the tool has when it is used for digging a node,
of this group, of the maximum level. For lower leveled nodes, the use count
is multiplied by 3^leveldiff.
- uses=10, leveldiff=0 -> actual_uses=10
- uses=10, leveldiff=1 -> actual_uses=30
- uses=10, leveldiff=2 -> actual_uses=90

**Maximum level**
Tells what is the maximum level of a node of this group that the tool will
be able to dig.

**Digging times**
List of digging times for different ratings of the group, for nodes of the
maximum level.
  * For example, as a lua table, ''times={2=2.00, 3=0.70}''. This would
    result the tool to be able to dig nodes that have a rating of 2 or 3
    for this group, and unable to dig the rating 1, which is the toughest.
    Unless there is a matching group that enables digging otherwise.
  * For entities, damage equals the amount of nodes dug in the time spent
    between hits, with a maximum time of ''full_punch_interval''.

Example definition of the capabilities of a tool
-------------------------------------------------
tool_capabilities = {
	full_punch_interval=1.5,
	max_drop_level=1,
	groupcaps={
		crumbly={maxlevel=2, uses=20, times={[1]=1.60, [2]=1.20, [3]=0.80}}
	}
}

This makes the tool be able to dig nodes that fullfill both of these:
- Have the **crumbly** group
- Have a **level** group less or equal to 2

Table of resulting digging times:
crumbly        0     1     2     3     4  <- level
     ->  0     -     -     -     -     -
         1  0.80  1.60  1.60     -     -
         2  0.60  1.20  1.20     -     -
         3  0.40  0.80  0.80     -     -

level diff:    2     1     0    -1    -2

Table of resulting tool uses:
     ->  0     -     -     -     -     -
         1   180    60    20     -     -
         2   180    60    20     -     -
         3   180    60    20     -     -

Notes:
- At crumbly=0, the node is not diggable.
- At crumbly=3, the level difference digging time divider kicks in and makes
  easy nodes to be quickly breakable.
- At level > 2, the node is not diggable, because it's level > maxlevel

Entity damage mechanism
------------------------
Damage calculation:
- Take the time spent after the last hit
- Limit time to full_punch_interval
- Take the damage groups, assume a node has them
- Damage in HP is the amount of nodes destroyed in this time.

Client predicts damage based on damage groups. Because of this, it is able to
give an immediate response when an entity is damaged or dies; the response is
pre-defined somehow (eg. by defining a sprite animation) (not implemented;
TODO).
- Currently a smoke puff will appear when an entity dies.

The group **immortal** will completely disable normal damage.

Entities can define a special armor group, which is **punch_operable**. This
group will disable the regular damage mechanism for players punching it by hand
or a non-tool item.

On the Lua side, every punch calls ''entity:on_punch(puncher,
time_from_last_punch, tool_capabilities, direction)''. This should never be
called directly, because damage is usually not handled by the entity itself.
  * ''puncher'' is the object performing the punch. Can be nil. Should never be
    accessed unless absolutely required.
  * ''time_from_last_punch'' is time from last punch (by puncher) or nil.
  * ''tool_capabilities'' can be nil.
  * ''direction'' is a unit vector, pointing from the source of the punch to
    the punched object.

To punch an entity/object in Lua, call ''object:punch(puncher, time_from_last_punch, tool_capabilities, direction)''.
  * Return value is tool wear.
  * Parameters are equal to the above callback.
  * If ''direction'' is nil and ''puncher'' is not nil, ''direction'' will be
    automatically filled in based on the location of ''puncher''.

Helper functions
-----------------
dump2(obj, name="_", dumped={})
^ Return object serialized as a string, handles reference loops
dump(obj, dumped={})
^ Return object serialized as a string
string:split(separator)
^ eg. string:split("a,b", ",") == {"a","b"}
string:trim()
^ eg. string.trim("\n \t\tfoo bar\t ") == "foo bar"
minetest.pos_to_string({x=X,y=Y,z=Z}) -> "(X,Y,Z)"
^ Convert position to a printable string

minetest namespace reference
-----------------------------
minetest.get_current_modname() -> string
minetest.get_modpath(modname) -> eg. "/home/user/.minetest/usermods/modname"
^ Useful for loading additional .lua modules or static data from mod
minetest.get_worldpath() -> eg. "/home/user/.minetest/world"
^ Useful for storing custom data
minetest.is_singleplayer()

minetest.debug(line)
^ Goes to dstream
minetest.log(line)
minetest.log(loglevel, line)
^ loglevel one of "error", "action", "info", "verbose"

Registration functions: (Call these only at load time)
minetest.register_entity(name, prototype table)
minetest.register_abm(abm definition)
minetest.register_node(name, node definition)
minetest.register_tool(name, item definition)
minetest.register_craftitem(name, item definition)
minetest.register_alias(name, convert_to)
minetest.register_craft(recipe)
minetest.register_globalstep(func(dtime))
minetest.register_on_placenode(func(pos, newnode, placer))
minetest.register_on_dignode(func(pos, oldnode, digger))
minetest.register_on_punchnode(func(pos, node, puncher))
minetest.register_on_generated(func(minp, maxp, blockseed))
minetest.register_on_newplayer(func(ObjectRef))
minetest.register_on_dieplayer(func(ObjectRef))
minetest.register_on_respawnplayer(func(ObjectRef))
^ return true in func to disable regular player placement
^ currently called _before_ repositioning of player occurs
minetest.register_on_chat_message(func(name, message))
minetest.register_chatcommand(cmd, chatcommand definition)
minetest.register_privilege(name, definition)
^ definition: "description text"
^ definition: {
      description = "description text",
      give_to_singleplayer = boolean, -- default: true
  }
minetest.register_authentication_handler(handler)
^ See minetest.builtin_auth_handler in builtin.lua for reference

Setting-related:
minetest.setting_set(name, value)
minetest.setting_get(name) -> string or nil
minetest.setting_getbool(name) -> boolean value or nil
minetest.add_to_creative_inventory(itemstring)

Authentication:
minetest.notify_authentication_modified(name)
^ Should be called by the authentication handler if privileges change.
^ To report everybody, set name=nil.
minetest.get_password_hash(name, raw_password)
^ Convert a name-password pair to a password hash that minetest can use
minetest.string_to_privs(str) -> {priv1=true,...}
minetest.privs_to_string(privs) -> "priv1,priv2,..."
^ Convert between two privilege representations
minetest.set_player_password(name, password_hash)
minetest.set_player_privs(name, {priv1=true,...})
minetest.get_player_privs(name) -> {priv1=true,...}
minetest.auth_reload()
^ These call the authentication handler
minetest.check_player_privs(name, {priv1=true,...}) -> bool, missing_privs
^ A quickhand for checking privileges

Chat:
minetest.chat_send_all(text)
minetest.chat_send_player(name, text)

Inventory:
minetest.get_inventory(location) -> InvRef
^ location = eg. {type="player", name="celeron55"}
                 {type="node", pos={x=, y=, z=}}

Item handling:
minetest.inventorycube(img1, img2, img3)
^ Returns a string for making an image of a cube (useful as an item image)
minetest.get_pointed_thing_position(pointed_thing, above)
^ Get position of a pointed_thing (that you can get from somewhere)
minetest.dir_to_facedir(dir)
^ Convert a vector to a facedir value, used in param2 for paramtype2="facedir"
minetest.dir_to_wallmounted(dir)
^ Convert a vector to a wallmounted value, used for paramtype2="wallmounted"
minetest.get_node_drops(nodename, toolname)
^ Returns list of item names.
^ Note: This will be removed or modified in a future version.

Defaults for the on_* item definition functions:
(These return the leftover itemstack)
minetest.item_place_node(itemstack, placer, pointed_thing)
^ Place item as a node
minetest.item_place_object(itemstack, placer, pointed_thing)
^ Place item as-is
minetest.item_place(itemstack, placer, pointed_thing)
^ Use one of the above based on what the item is.
minetest.item_drop(itemstack, dropper, pos)
^ Drop the item
minetest.item_eat(hp_change, replace_with_item)
^ Eat the item. replace_with_item can be nil.

Defaults for the on_punch and on_dig node definition callbacks:
minetest.node_punch(pos, node, puncher)
^ Calls functions registered by minetest.register_on_punchnode()
minetest.node_dig(pos, node, digger)
^ Checks if node can be dug, puts item into inventory, removes node
^ Calls functions registered by minetest.registered_on_dignodes()

Sounds:
minetest.sound_play(spec, parameters) -> handle
^ spec = SimpleSoundSpec
^ parameters = sound parameter table
minetest.sound_stop(handle)

Timing:
minetest.after(time, func, param)
^ Call function after time seconds
^ param is optional; to pass multiple parameters, pass a table.

Random:
minetest.get_connected_players() -> list of ObjectRefs
minetest.hash_node_position({x=,y=,z=}) -> 48-bit integer
^ Gives a unique hash number for a node position (16+16+16=48bit)

Global objects:
minetest.env - environment reference

Global tables:
minetest.registered_items
^ List of registered items, indexed by name
minetest.registered_nodes
^ List of registered node definitions, indexed by name
minetest.registered_craftitems
^ List of registered craft item definitions, indexed by name
minetest.registered_tools
^ List of registered tool definitions, indexed by name
minetest.registered_entities
^ List of registered entity prototypes, indexed by name
minetest.object_refs
^ List of object references, indexed by active object id
minetest.luaentities
^ List of lua entities, indexed by active object id

Deprecated but defined for backwards compatibility:
minetest.digprop_constanttime(time)
minetest.digprop_stonelike(toughness)
minetest.digprop_dirtlike(toughness)
minetest.digprop_gravellike(toughness)
minetest.digprop_woodlike(toughness)
minetest.digprop_leaveslike(toughness)
minetest.digprop_glasslike(toughness)

Class reference
----------------
EnvRef: basically ServerEnvironment and ServerMap combined.
methods:
- set_node(pos, node)
- add_node(pos, node): alias set_node(pos, node)
- remove_node(pos): equivalent to set_node(pos, "air")
- get_node(pos)
  ^ Returns {name="ignore", ...} for unloaded area
- get_node_or_nil(pos)
  ^ Returns nil for unloaded area
- get_node_light(pos, timeofday) -> 0...15 or nil
  ^ timeofday: nil = current time, 0 = night, 0.5 = day
- add_entity(pos, name): Spawn Lua-defined entity at position
  ^ Returns ObjectRef, or nil if failed
- add_item(pos, itemstring): Spawn item
  ^ Returns ObjectRef, or nil if failed
- get_meta(pos) -- Get a NodeMetaRef at that position
- get_player_by_name(name) -- Get an ObjectRef to a player
- get_objects_inside_radius(pos, radius)
- set_timeofday(val): val: 0...1; 0 = midnight, 0.5 = midday
- get_timeofday()
Deprecated:
- add_rat(pos): Add C++ rat object (no-op)
- add_firefly(pos): Add C++ firefly object (no-op)

NodeMetaRef (this stuff is subject to change in a future version)
methods:
- get_type()
- allows_text_input()
- set_text(text) -- eg. set the text of a sign
- get_text()
- get_owner()
- set_owner(string)
Generic node metadata specific:
- set_infotext(infotext)
- get_inventory() -> InvRef
- set_inventory_draw_spec(string)
- set_allow_text_input(bool)
- set_allow_removal(bool)
- set_enforce_owner(bool)
- is_inventory_modified()
- reset_inventory_modified()
- is_text_modified()
- reset_text_modified()
- set_string(name, value)
- get_string(name)

ObjectRef: Moving things in the game are generally these
(basically reference to a C++ ServerActiveObject)
methods:
- remove(): remove object (after returning from Lua)
- getpos() -> {x=num, y=num, z=num}
- setpos(pos); pos={x=num, y=num, z=num}
- moveto(pos, continuous=false): interpolated move
- punch(puncher, time_from_last_punch, tool_capabilities, direction)
  ^ puncher = an another ObjectRef,
  ^ time_from_last_punch = time since last punch action of the puncher
- right_click(clicker); clicker = an another ObjectRef
- get_hp(): returns number of hitpoints (2 * number of hearts)
- set_hp(hp): set number of hitpoints (2 * number of hearts)
- get_inventory() -> InvRef
- get_wield_list(): returns the name of the inventory list the wielded item is in
- get_wield_index(): returns the index of the wielded item
- get_wielded_item() -> ItemStack
- set_wielded_item(item): replaces the wielded item, returns true if successful
- set_armor_groups({group1=rating, group2=rating, ...})
- set_properties(object property table)
LuaEntitySAO-only: (no-op for other objects)
- setvelocity({x=num, y=num, z=num})
- getvelocity() -> {x=num, y=num, z=num}
- setacceleration({x=num, y=num, z=num})
- getacceleration() -> {x=num, y=num, z=num}
- setyaw(radians)
- getyaw() -> radians
- settexturemod(mod)
- setsprite(p={x=0,y=0}, num_frames=1, framelength=0.2,
-           select_horiz_by_yawpitch=false)
- ^ Select sprite from spritesheet with optional animation and DM-style
-   texture selection based on yaw relative to camera
- get_entity_name() (DEPRECATED: Will be removed in a future version)
- get_luaentity()
Player-only: (no-op for other objects)
- get_player_name(): will return nil if is not a player
- get_look_dir(): get camera direction as a unit vector
- get_look_pitch(): pitch in radians
- get_look_yaw(): yaw in radians (wraps around pretty randomly as of now)

InvRef: Reference to an inventory
methods:
- get_size(listname): get size of a list
- set_size(listname, size): set size of a list
- get_stack(listname, i): get a copy of stack index i in list
- set_stack(listname, i, stack): copy stack to index i in list
- get_list(listname): return full list
- set_list(listname, list): set full list (size will not change)
- add_item(listname, stack): add item somewhere in list, returns leftover ItemStack
- room_for_item(listname, stack): returns true if the stack of items
    can be fully added to the list
- contains_item(listname, stack): returns true if the stack of items
    can be fully taken from the list
  remove_item(listname, stack): take as many items as specified from the list,
    returns the items that were actually removed (as an ItemStack)

ItemStack: A stack of items.
- Can be created via ItemStack(itemstack or itemstring or table or nil)
methods:
- is_empty(): return true if stack is empty
- get_name(): returns item name (e.g. "default:stone")
- get_count(): returns number of items on the stack
- get_wear(): returns tool wear (0-65535), 0 for non-tools
- get_metadata(): returns metadata (a string attached to an item stack)
- clear(): removes all items from the stack, making it empty
- replace(item): replace the contents of this stack (item can also
    be an itemstring or table)
- to_string(): returns the stack in itemstring form
- to_table(): returns the stack in Lua table form
- get_stack_max(): returns the maximum size of the stack (depends on the item)
- get_free_space(): returns get_stack_max() - get_count()
- is_known(): returns true if the item name refers to a defined item type
- get_definition(): returns the item definition table
- get_tool_capabilities(): returns the digging properties of the item,
  ^ or those of the hand if none are defined for this item type
- add_wear(amount): increases wear by amount if the item is a tool
- add_item(item): put some item or stack onto this stack,
  ^ returns leftover ItemStack
- item_fits(item): returns true if item or stack can be fully added to this one
- take_item(n): take (and remove) up to n items from this stack
  ^ returns taken ItemStack
  ^ if n is omitted, n=1 is used
- peek_item(n): copy (don't remove) up to n items from this stack
  ^ returns copied ItemStack
  ^ if n is omitted, n=1 is used

PseudoRandom: A pseudorandom number generator
- Can be created via PseudoRandom(seed)
methods:
- next(): return next integer random number [0...32767]
- next(min, max): return next integer random number [min...max]
                  (max - min) must be 32767 or <= 6553 due to the simple
                  implementation making bad distribution otherwise.

Registered entities
--------------------
- Functions receive a "luaentity" as self:
  - It has the member .name, which is the registered name ("mod:thing")
  - It has the member .object, which is an ObjectRef pointing to the object
  - The original prototype stuff is visible directly via a metatable
- Callbacks:
  - on_activate(self, staticdata)
    ^ Called when the object is instantiated.
  - on_step(self, dtime)
    ^ Called on every server tick (dtime is usually 0.05 seconds)
  - on_punch(self, puncher, time_from_last_punch, tool_capabilities, dir)
    ^ Called when somebody punches the object.
    ^ Note that you probably want to handle most punches using the
      automatic armor group system.
    ^ puncher: ObjectRef (can be nil)
    ^ time_from_last_punch: Meant for disallowing spamming of clicks (can be nil)
    ^ tool_capabilities: capability table of used tool (can be nil)
	^ dir: unit vector of direction of punch. Always defined. Points from
	       the puncher to the punched.
  - on_rightclick(self, clicker)
  - get_staticdata(self)
    ^ Should return a string that will be passed to on_activate when
      the object is instantiated the next time.

Definition tables
------------------

Object Properties
{
    physical = true,
    collisionbox = {-0.5,-0.5,-0.5, 0.5,0.5,0.5},
    visual = "cube"/"sprite"/"upright_sprite",
    visual_size = {x=1, y=1},
    textures = {}, -- number of required textures depends on visual
    spritediv = {x=1, y=1},
    initial_sprite_basepos = {x=0, y=0},
    is_visible = true,
    makes_footstep_sound = false,
}

Entity definition (register_entity)
{
    (Deprecated: Everything in object properties is read directly from here)
    
    initial_properties = <initial object properties>,

    on_activate = function(self, staticdata),
    on_step = function(self, dtime),
    on_punch = function(self, hitter),
    on_rightclick = function(self, clicker),
    get_staticdata = function(self),
    ^ Called sometimes; the string returned is passed to on_activate when
      the entity is re-activated from static state
    
    # Also you can define arbitrary member variables here
    myvariable = whatever,
}

ABM (ActiveBlockModifier) definition (register_abm)
{
    -- In the following two fields, also group:groupname will work.
    nodenames = {"default:lava_source"},
    neighbors = {"default:water_source", "default:water_flowing"}, -- (any of these)
     ^ If left out or empty, any neighbor will do
    interval = 1.0, -- (operation interval)
    chance = 1, -- (chance of trigger is 1.0/this)
    action = func(pos, node, active_object_count, active_object_count_wider),
}

Item definition (register_node, register_craftitem, register_tool)
{
    description = "Steel Axe",
    groups = {}, -- key=name, value=rating; rating=1..3.
                    if rating not applicable, use 1.
                    eg. {wool=1, fluffy=3}
                        {soil=2, outerspace=1, crumbly=1}
                        {bendy=2, snappy=1},
                        {hard=1, metal=1, spikes=1}
    inventory_image = "default_tool_steelaxe.png",
    wield_image = "",
    wield_scale = {x=1,y=1,z=1},
    stack_max = 99,
    liquids_pointable = false,
    tool_capabilities = {
        full_punch_interval = 1.0,
        max_drop_level=0,
        groupcaps={
            -- For example:
            fleshy={times={[2]=0.80, [3]=0.40}, maxwear=0.05, maxlevel=1},
            snappy={times={[2]=0.80, [3]=0.40}, maxwear=0.05, maxlevel=1},
            choppy={times={[3]=0.90}, maxwear=0.05, maxlevel=0}
        }
    }
    on_drop = func(itemstack, dropper, pos),
    on_place = func(itemstack, placer, pointed_thing),
    on_use = func(itemstack, user, pointed_thing),
    ^ Function must return either nil if no item shall be removed from
      inventory, or an itemstack to replace the original itemstack.
        eg. itemstack:take_item(); return itemstack
    ^ Otherwise, the function is free to do what it wants.
    ^ The default functions handle regular use cases.
}

Node definition (register_node)
{
    <all fields allowed in item definitions>,

    drawtype = "normal",
    visual_scale = 1.0,
    tile_images = {"default_unknown_block.png"},
    special_materials = {
        {image="", backface_culling=true},
        {image="", backface_culling=true},
    },
    alpha = 255,
    post_effect_color = {a=0, r=0, g=0, b=0},
    paramtype = "none",
    paramtype2 = "none",
    is_ground_content = false,
    sunlight_propagates = false,
    walkable = true,
    pointable = true,
    diggable = true,
    climbable = false,
    buildable_to = false,
    drop = "",
    -- alternatively drop = { max_items = ..., items = { ... } }
    metadata_name = "",
    liquidtype = "none",
    liquid_alternative_flowing = "",
    liquid_alternative_source = "",
    liquid_viscosity = 0,
    light_source = 0,
    damage_per_second = 0,
    selection_box = {type="regular"},
    legacy_facedir_simple = false, -- Support maps made in and before January 2012
    legacy_wallmounted = false, -- Support maps made in and before January 2012
    sounds = {
        footstep = <SimpleSoundSpec>,
        dig = <SimpleSoundSpec>, -- "__group" = group-based sound (default)
        dug = <SimpleSoundSpec>,
    },
}

Recipe: (register_craft)
{
    output = 'default:pick_stone',
    recipe = {
        {'default:cobble', 'default:cobble', 'default:cobble'},
        {'', 'default:stick', ''},
        {'', 'default:stick', ''},
    },
    replacements = <optional list of item pairs,
                    replace one input item with another item on crafting>
}

Recipe (shapeless):
{
    type = "shapeless",
    output = 'mushrooms:mushroom_stew',
    recipe = {
        "mushrooms:bowl",
        "mushrooms:mushroom_brown",
        "mushrooms:mushroom_red",
    },
    replacements = <optional list of item pairs,
                    replace one input item with another item on crafting>
}

Recipe (tool repair):
{
    type = "toolrepair",
    additional_wear = -0.02,
}

Recipe (cooking):
{
    type = "cooking",
    output = "default:glass",
    recipe = "default:sand",
    cooktime = 3,
}

Recipe (furnace fuel):
{
    type = "fuel",
    recipe = "default:leaves",
    burntime = 1,
}

Chatcommand definition (register_chatcommand)
{
    params = "<name> <privilege>", -- short parameter description
    description = "Remove privilege from player", -- full description
    privs = {privs=true}, -- require the "privs" privilege to run
    func = function(name, param), -- called when command is run
}