Repixture/mods/rp_mobs/API.md

Repixture Mobs API

NOTE: This API is EXPERIMENTAL and subject to change! Use at your own risk.

This is the API documentation for the Repixture Mobs API. This is the document you want to read if you want to develop your own Repixture mobs.

Core concepts

Mobs

In this mod, a "mob" refers a non-player entity with added capabilities like a task queue. Mobs can be used to implement things like animals or monsters.

Tasks, microtasks and task queues

The heart of this mod are tasks. A task is a single defined goal that a mob has to achieve in some manner. Every task can either succeed or fail. Tasks include high-level goals such as "find and eat food", "flee from the player", "kill the player", "roam randomly", etc.

Additionally, every task consists of a number of microtasks. These are intended for more low-level and simple activities such as "go to point XYZ", "jump", "attack in direction A". Microtasks are executed sequentially and can either succeed or fail. If a microtask fails, the task it is part of will end. If all microtasks in a task have finished, the task also ends.

To use tasks, they must be initialized by calling rp_mobs.init_tasks in on_activate and be handled (i.e. executed) every step by calling rp_mobs.handle_tasks in on_step.

Finally, task queues organize the execution of tasks. A task queue is a sequence of tasks that get executed in order. Tasks get automatically removed from the queue once finished. Task queues also optionally have a number of decider function which are called to determine which tasks to add next.

A mob can have any number of task queues active at a time. While tasks and microtasks are executed sequentially, task queues run in parallel.

Task queues, tasks and microtask form a tree-like structure, like so:

Task queue 1
|
`- Task 1
   |
   `- Microtask 1
   `- Microtask 2
|
`- Task 2
   `- Microtask 1
   `- Microtask 2

So on the top level, you have task queues, which consist of tasks, which in turn consist of microtasks.

Physics and movement

This mod doesn't handle physics. Just use Minetest’s built-in functions like set_velocity and set_acceleration.

There’s one exception: Gravity. This mod provides a default gravity vector at rp_mobs.GRAVITY_VECTOR.

To activate gravity for a mob, you use the set_acceleration microtask template (see the section about task templates).

Registering a mob

You add (register) a mob via rp_mobs.register_mob. Mob definitions in this API are very low-level and similar to typical entity definitions in Minetest. You still have to provide a full entity definition via entity_definition including the callback functions like on_activate and on_rightclick.

You're supposed to use the Repixture Mob API functionality by inserting the various helper functions into the callbacks like on_step and on_activate where appropriate.

A template for a minimal mob looks like this:

rp_mobs.register_mob("MOBNAME", {
	description = "MOB DESCRIPTION",
	drops = { ADD_YOUR_DROPS_HERE },
	entity_definition = {
		initial_properties = {
			-- Add the initial entity properties here
			-- e.g. physical, hp_max, textures, etc.
		},
		on_activate = function(self, staticdata)
			rp_mobs.init_mob(self)
			rp_mobs.restore_state(self, staticdata)
			rp_mobs.init_tasks(self)
		end,
		on_step = function(self, dtime, moveresult)
			rp_mobs.handle_dying(self, dtime, moveresult)
			rp_mobs.handle_tasks(self, dtime, moveresult)
		end,
		get_staticdata = rp_mobs.get_staticdata_default,
		on_death = rp_mobs.on_death_default,
		on_punch = rp_mobs.on_punch_default,
	},
})

Data structures

This section defines the data structures used in the functions below.

Task

A task is just a table. It can have the following fields:

• label: Brief string explaining what the task does. Only for debug
• task_queue: Read-only reference to the task queue this task is part of or nil. Will be set automatically when the task is added to a task queue.

Tasks can be created with rp_mobs.create_task.

The task's microtasks are stored internally. Use rp_mobs.add_microtask_to_task to add a microtask to a task.

Microtask

A microtask is a table with the following fields:

• label: Same as for tasks
• on_step: Called every step of the mob. Handle the microtask behavior here
• is_finished: Must returns <finished>, <success> <finished> must be true once the microtask is finished. <success> (optional) can be set when the microtask finished to either true if it successfully finishes (default) or false if it finishes in failure
• on_end: Called when the microtask has ended. Useful for cleaning up state
• on_start: Called when the microtask has begun. Called just before on_step
• singlestep: If true, this microtask will run for only 1 step and automatically finishes (default: false)
• statedata: Table containing data that can be modified and read at runtime
• task: Read-only reference to the task this microtask is part of, or nil. Will be set automatically when it is added to a task

Every microtask needs to have on_step and either is_finished or singlestep = true. All other fields are optional. It is not allowed to add any fields not listed above.

is_finished, on_end and on_start have parameters self, mob with self being a reference to the microtask table itself and mob being the mob object that is affected.

on_step has the parameters self, mob, dtime, moveresult, where dtime is the time in seconds that have passed since it was last called, or 0 on the first call (like for the entity on_step function), and moveresult is the moveresult of the entity on_step function (only available if physical=true in the entity definition, otherwise it'll be nil).

The normal order of execution of the callbacks is as follows: on_start is called once right after the microtask started. Then, in a a loop, first is_finished and then on_step is called. If is_finished returned false, the microtask immediately finishes (skipping the next on_step), causing on_end to get called.

In case of a singlestep microtask, the execution order is simply on_start, on_step (once) and on_end. is_finished is not called.

When a microtask finishes, it either ends in success or failure. The default is success. Setting the success return value of is_finished to false will finish the microtask in failure. If a microtask finished in failure, the task it contains will end, skipping the remaining microtasks. singlestep microtasks always end in success.

The statedata field can be used to associate arbitrary data with the microtask in order to preserve some state. You may read and write to it in functions like on_step.

Microtasks can be created with rp_mobs.create_microtask.

Subsystems

Subsystems implement core mob features. The task handling is also a subsystem.

Each subsystem is enabled by adding both a handle_* function in on_step and an init_* function in on_activate. Some subsystems only require one of these functions.

The handle_* function in on_step must be called on every step. Failing to do so leads to undefined behavior.

For example, to enable the Tasks subsystem, call rp_mobs.init_tasks in on_activate of the mob entity definition, and rp_mobs.handle_tasks in on_step. See the function reference for details.

Some subsystems are mandatory (see overview below).

Subsystem overview

This overview is a list of all subsystems and the required functions you need to call:

Subsystem   | on_activate function     | on_step function
------------+--------------------------+----------------------------
Core*       | rp_mobs.init_mob         | **
Tasks*      | rp_mobs.init_tasks       | rp_mobs.handle_tasks
Dying       | **                       | rp_mobs.handle_dying
Node damage | rp_mobs.init_node_damage | rp_mobs.handle_node_damage***
Fall damage | rp_mobs.init_fall_damage | rp_mobs.handle_fall_damage***
Breath      | rp_mobs.init_breath      | rp_mobs.handle_breath***
Breeding    | **                       | rp_mobs.handle_breeding

*   = mandatory
**  = no function required
*** = can be replaced with rp_mobs.handle_environment_damage

Core subsystem

The core subsystem must always be added to the mob. It does initialization work that is mandatory for all mobs. Add rp_mobs.init_mob to the beginning of the on_activate function.

Dying

An entity “dies” in Minetest when its HP reaches 0, which instantly removes it and triggers the on_death function.

We do not like instant removal so this subsystem provides a simple graphical death effect and delay. This flips over the mob and calls a special dying_step function every step. This function is used by the mob to handle death physics stuff.

While dying, no tasks or microtasks are run. The mob is still visible but all player interactions are disabled. After a short delay, the mob disappears in a cloud of dust by setting the HP to 0, causing on_death to be called.

To use this subsystem, add rp_mobs.handle_dying into on_step.

IMPORTANT: You also must follow a restriction: Never call set_hp to damage the mob. Instead, punch the mob with the built-in punch function or call rp_mobs.damage.

Internally, this subsystem works by storing a variable for the mob to hold the dead/alive state. It can be queried with rp_mobs.is_alive. When the mob has received fatal damage, the HP remains at 1 but the mob counts as dead.

If this subsystem is not used, the mob will instantly disappear when the HP reaches 0. But on_death is still called because this is built-in by Minetest.

Node damage

Node damage enables the mob being vulnerable to nodes with the damage_per_second field. If you want your mob to use this, add rp_mobs.init_node_damage to on_activate and rp_mobs.handle_node_damage to on_step. Read the documentation of these functions to learn more about how the node damage mechanic works.

Node damage can be temporarily disabled during the mob’s lifetime by setting the entity field _get_node_damage to false.

Fall damage

Fall damage hurts the mob when it hits the ground too hard. The fall damage calculation works differently than for players (see rp_mobs.handle_fall_damage for details.

To enable fall damage , add rp_mobs.init_fall_damage in on_activate and rp_mobs.handle_fall_damage in on_step.

Breath

The breath subsystem enables breath and a drowning mechanic. This makes mobs take drowning damage when inside a particular node.

If you want your mob to use this, add rp_mobs.init_breath to on_activate and rp_mobs.handle_drowning in on_step. Read the documentation of these functions to learn more about the drowning mechanic in general.

The drowning status can also be changed during the mob’s lifetime in on_step by manipulating the mob fields (see the mob field reference).

Breeding

Breeding will make mobs mate and create offspring. To enable, call rp_mobs.handle_breeding in on_step. You also need to add the tag "child_exists" to the mob definition.

In particular, to breed, two adult mobs of the same type need to be “horny” and close to each other. Then, a random mob of the pair gets pregnant and will soon spawn a child mob. The child mob will grow to an adult after some time.

There are two ways to make a mob horny:

1. Call rp_mobs.feed_tame_breed in on_rightclick (i.e. player gives mob enough food)
2. Call rp_mobs.make_horny to instantly make the mob horny

Only adults should be horny.

Mob field reference

Mob entities use a bunch of custom fields. You may read and edit them at runtime. These fields are available:

Status

• _tamed: true if mob is tame
• _tame_level: tame level. Starts at 0 and increases for any food given, used to trigger taming
• _horny_level: 'horny' level. Starts at 0 and increases for any food given to an adult, used to trigger horny mode
• _child: true if mob is a child
• _horny: true if mob is “horny”. If another horny mob is nearby, they will mate and spawn a child soon
• _pregnant: true if mob is pregnant and about to spawn a child

Textures

NOTE: You must update these whenever you want to change a mob's texture. If the mob does not use a custom child texture, _textures_child can be skipped.

• _textures_adult: Stores a copy of the current mob textures table for the mob in adult form
• _textures_child: Stores a copy of the current mob textures table for the mob in child form

Damage

• _get_node_damage: true when mob can take damage from nodes (damage_per_second) (default: false)
• _get_fall_damage: true when mob can take fall damage (default: false)
• _can_drown: true when mob has breath and can drown in nodes with drowning attribute (default: false)
• _drowning_point: See rp_mobs.init_breath.
• _node_damage_points: See rp_mobs_init_node_damage.
• _breath_max: Maximum breath (ignored if _can_drown isn’t true)
• _breath: Current breath (ignored if _can_drown isn’t true)

Please note: You must call rp_mobs.init_node_damage before you touch the _get_node_damage field. You must call rp_mobs.init_breath before you touch the breath/drowning fields.

Internal use

A bunch of fields are meant for internal use by rp_mobs. Do not change them. Reading them is fine.

• _cmi_is_mob: Always true. Indicates the entity is a mob
• _child_grow_timer: time the mob has been a child (seconds)
• _horny_timer: time the mob has been horny (seconds)
• _breed_check_timer: timer for the breed check (seconds)
• _pregnant_timer: time the mob has been pregnant (seconds)
• _last_feeder: Name of the last player who fed the mob
• _dying: Is true when mob is currently dying and about to be removed
• _dying_timer: time the mob has been in the dying state (seconds)

Function reference

Registrations

rp_mobs.register_mob(mobname, def)

Register a mob with the entity identifier mobname and definition def. The mob definition will be stored under rp_mobs.registered_mobs[mobname]. The field _cmi_is_mob=true will be set automatically for all mobs and can be used to check whether any given entity is a mob.

def is a definition table with the following optional fields:

• description: Mob name used for display purposes (can be translated)
• entity_definition: Entity definition table. Put everything in here that is also used for normal entities (on_step, on_activate, initial_properties, etc.).
  • It may also contain this custom function:
    • _on_capture(self, capturer): Called when a mob capture is attempted by capturer (a player). Triggered by rp_mobs.call_on_capture
• drops: Items to drop (see 'Drop table' below) on death when mob dies as adult (default: empty table)
• child_drops: Items to drop when mob dies as child (default: empty table)
• drop_func(self): (optional) Called when mob is dropping its death drop items. Must return table of items to drop. These items are dropped on top of the items in drops and child_drops. This function must not manipulate the mob in any way.
• default_sounds: Table of default sound names to play automatically on built-in events. Sounds will be played by rp_mobs.default_mob_sound
  • death: When mob dies
  • damage: When mob takes non-fatal damage
  • punch_no_damage: When mob was punched but took no damage
  • eat: When mob eats something (this has a default sound)
  • call: Occasional mob call (only played manually)
  • horny: When mob becomes horny
  • give_birth: When mob gives birth to a child
• front_body_point: A point of the front side of the mob, specified as offset vector from the mob position. Used to "see" forwards to detect dangerous land (cliffs, damaging blocks, etc.) Should be on the front face of the mob model and roughly in the center of that side.
• path_check_point: A point that is used to compare the position to the path goal position, specified as offset vector from the mob position. This point is used to check whether a path point has been 'reached' for the follow_path* microtask templates.
• dead_y_offset: Y offset of collisionbox when mob is in 'dying' state. Set this to a number so that the mob lies on top of the ground (it should neither float nor be inside the ground)
• textures_child: If set, this will be the mob texture for the mob as a child. Same syntax as textures of the entity definition. Adult mobs will use textures
• animations: Table of available mob animations
  • The keys are string identifies for each animation, like "walk"
  • The values are tables with the following fields:
    • frame_range: Same as frame_range in object:set_animation
    • default_frame_speed: Default frame_speed (from object:set_animation) when this animation is played
  • Built-in animations are:
    • "idle": Played when mob has nothing to do (empty task queue)
    • "dead_static": Played when mob is dead (there normally should be no animation, just a static frame)
• tags: Table of tags.
  • Tags are arbitrary strings used to logically categorize the mob.
  • The table keys are tag names and value for each key must always be 1.
  • You can check if a mob has a tag with rp_mobs.has_tag or rp_mobs.mobdef_has_tag.
  • Built-in tag names:
    • "animal": This mob is an animal. Some items and achievements check for this tag
    • "peaceful": Mob is considered 'peaceful' towards players if unprovoked. It normally leaves the player alone. Peaceful mobs may still turn hostile when provoked. Mobs that start hostile towards the player do not count as peaceful. If the setting spawn_peaceful_only is enabled, only mobs with this tag can spawn.
    • "child_exists": Mob has a functional child version. This tag is only for informing other mobs; it does not have an effect in the rp_mobs code
  • Example: tags = { animal = 1, peaceful = 1, exploder = 1 }
    • A peaceful animal, plus a custom "exploder" tag.

Drop table

For the arguments drops and child_drops, two types of values are supported:

1. List of itemstrings: Will drop every item in this list
2. List of drop probabilities: Will drop items by a given chance
   • name: Technical itemname
   • chance: Chance given in 1/chance for this item to drop
   • min: Minimum item count when it drops
   • max: Maximum item count when it drops

rp_mobs.register_mob_item(mobname, invimg, desc, on_create_capture_item)

Registers an item representing a mob. It can be used by players to spawn the mob by placing it. This item is also used when a mob is captured.

The mob item may contain metadata to store the mob's HP and internal state of the mob.

• mobname: Mob identifier
• invimg: Inventory image texture
• desc: Description for inventory
• on_create_capture_item: (optional) Function is called with arguments mob, itemstack when mob has been captured and is becoming an itemstack. You can use this function to modify the itemstack's metadata, e.g. to use a item image override if the mob can have different appearances. Must return an itemstack for the itemstack that is actually created.

rp_mobs.register_capture_tool(itemname, definition)

Registers an existing tool as a capture tool.

• itemname: Item name of the item that captures
• definition: A table with these fields:
  • uses: Number of uses before the tool breaks. 0 = unlimited
  • sound: (optional) Name of sound that plays when “swinging” the tool
  • sound_gain: (optional) Gain of that sound (as in SimpleSoundSpec)
  • sound_max_hear_distance: (optional) max_hear_distance of that sound (as in SimpleSoundSpec)

This mod comes with a lasso (rp_mobs:lasso) and a net (rp_mobs:net) by default.

Default entity handlers

These functions should be set as the callback functions of the mob entity. The code will usually look like this:

get_staticdata = rp_mobs.get_staticdata_default,	-- required
on_death = rp_mobs.on_death_default,			-- optional, custom handler recommended
on_punch = rp_mobs.on_punch_default,			-- optional

rp_mobs.get_staticdata_default(mob)

The default handler for get_staticdata of the mob's entity definition. This will handle the staticdata of the mob for you. All the mob's internal information will be stored including the _custom_state. _temp_custom_state will be discarded.

This function must be set explicitly for every mob.

Set get_staticdata = rp_mobs.get_staticdata_default to use this.

rp_mobs.on_death_default(mob, killer)

The default handler for on_death of the mob's entity definition. It should be set explicitly for every mob, unless you want to have a custom death handling. Currently, the default death handler just drops the mob death items.

Set on_death = rp_mobs.on_death_default to use the default death behavior.

Remember that on_death is a built-in Minetest event, so it is triggered even if the mob doesn't use the 'Dying' subsystem.

rp_mobs.on_punch_default(mob, puncher, time_from_last_punch, tool_capabilities, dir, damage)

Default on_punch handler of mob. Set this function to on_punch. The arguments are the same as for on_punch.

This will play a the damage sound if the mob took damage, otherwise, hit_no_damage is played (if the sound exists).

on_activate functions

These are functions to be used in the on_activate handler to initialize certain subsystems, like tasks.

Calling rp_mobs.init_mob, rp_mobs.restore_state and rp_mobs.init_tasks in on_activate are required, but everything else is optional depending on your needs.

rp_mobs.init_mob(mob)

This initializes the mob and does initialization work in order to do things that are required for all mobs.

This function must be called in on_activate before any other mob-related function.

rp_mobs.restore_state(mob, staticdata)

This will restore the mob's state data from the given staticdata in on_activate.

This must be called in on_activate before any other mob-related function except rp_mobs.init_mob.

rp_mobs.init_tasks(mob)

Initialize the task and microtask queues for the mob. This is supposed to go into on_activate of the entity definition.

This must be called in on_activate before any other mob-related function except rp_mobs.init_mob and rp_mobs.restore_state.

rp_mobs.init_breath(mob, can_drown, def)

Initializes the breath and drowning mechanic for the given mob. If you want the mob to have this, put this into on_activate.

If this is the first time the function is called, drowning and associated entity fields will be initialized. On subsequent calls, this function does nothing because the fields are already initialized.

• self: The mob
• can_drown: If true, drowning is possible, otherwise, it is not.
• def: A table with the following fields:
  • breath_max: Maximum (and initial) breath points. Positive number
  • drowning_point: Optional position offset vector that will be checked when doing the drowning check. It’s an offset from the mob position (get_pos()). If the node at the drowning point is a drowning node, the mob can drown. Default: no offset

rp_mobs.init_node_damage(mob, get_node_damage, def)

Initializes the node damage mechanic for the given mob, activating damage from nodes with damage_per_second. If you want the mob to have this, put this into on_activate.

Node damage is dealt by checking one or more "node damage points" for a node with node damage. By default, the mob position (get_pos()) is checked.

Negative damage heals the mob.

If this is the first time the function is called, the associated entity fields will be initialized. On subsequent calls, this function does nothing because the fields are already initialized.

Parameters:

• mob: The mob
• get_node_damage: If true, mob will receive damage from nodes
• def: A table with the following field:
  • node_damage_points: Optional list of position offset vectors that will be checked when doing the node damage check. Each vector is an offset from the mob position (get_pos()). If any of the checked positions has a node with a non-zero damage_per_second, then the node with the highest such value will be the damage dealt. Default: no offset

Recommendations:

It is strongly recommended you always explicitly define the node damage point(s).

For small mobs, one node damage point is sufficient. For large mobs (that usually occupy a space much larger than 1 node), multiple points should be used. Each damage point should be inside the mob's "body" and be roughly centered. Use as few points as possible for performance reasons, and don't put them too close to each other.

rp_mobs.init_fall_damage(mob, get_fall_damage)

Initializes the fall damage for the given mob, If you want the mob to have this, put this into on_activate.

If this is the first time the function is called, the associated entity fields will be initialized. On subsequent calls, this function does nothing because the fields are already initialized.

Parameters:

• self: The mob
• get_fall_damage: If true, mob will receive fall damage

Subsystems: on_step handlers

These are functions you need to call in the on_step callback function of the mob entity in order for a subsystem to work properly. Each of these functions assumes the corresponding rp_mobs.init_* function (if any) has been called before.

rp_mobs.handle_tasks(mob, dtime, moveresult)

Handle the task queues, tasks, microtasks of the mob for a single step. Required for the task system to work. This is supposed to go into on_step of the entity definition. It must be called every step.

dtime and moveresult must be passed from the arguments of the same name of the entity’s on_step.

rp_mobs.handle_dying(self, dtime, moveresult, dying_step)

Handles the dying state of the mob if the mob has been killed. If the internal mob state _dying is true, the dying effect is applied and the mob gets removed after a short delay, triggering the on_death callback. It is recommended to put this function before any other rp_mobs subsystem calls.

See the section about the “Dying” subsystem for details.

Parameters:

• self: Reference to mob object
• dtime: Same as for the entity’s on_step
• moveresult: Same as for the entity’s on_step
• dying_step: Optional function with signature self, dtime, moveresult that is called every step while the mob is in dying state

rp_mobs.handle_node_damage(mob, dtime)

Handles node damage for the mob if the entity field _get_node_damage is true. Node damage is taken when the mob is inside any node with a non-zero damage_per_second. Negative damage heals the mob.

See rp_mobs.init_node_damage for details on how the mod determines when the mob is inside such a node.

Must be called in the on_step function in every step. dtime is the dtime argument of on_step.

rp_mobs.handle_fall_damage(mob, dtime, moveresult)

Handles fall damage for the mob if the entity field _get_fall_damage is true.

Fall damage is calculated differently than for players and there is no guarantee the calculation algorithm will be forwards-compatible. It increases linearly with the fall height. Fall damage is further- more modified by the add_fall_damage_percent group if falling on a node. Adding the armor group add_fall_damage_percent will also modify the fall damage the mob will receive (like for players, see lua_api.md).

This function must be called in the on_step function in every step. dtime and moveresult are the same as in on_step.

rp_mobs.handle_drowning(mob, dtime)

Handles breath and drowning damage for the mob if the entity field _can_drown is true.

Mob drowning is meant to closely reflect player drowning.

This function requires that rp_mobs.init_breath has been called in on_activate before.

Technically, this function checks if the mob’s drowning point is inside a node with a non-zero non-nil drowning field. If this is the case, the internal _breath will be reduced in a regular interval. If _breath reaches zero, the mob will take damage equal to the node’s drowning value. If the mob is in a non-drowning node, it will regain breath up to _breath_max. In "ignore" nodes, breath will not be changed.

By default, the mob position will be checked to determine which node is checked for the drowning field. If _drowning_point is set, is must be a vector added to the mob position to check a different position. This is usually where the mob’s “head” is. The drowning point must be inside the collisionbox, otherwise the mob might regain breath when touching a wall. The drowning point will automatically be rotated with the mob’s yaw.

Must be called in the on_step function in every step. dtime is the dtime argument of on_step.

rp_mobs.handle_environment_damage(mob, dtime, moveresult)

Handle all environment damages. This is is the same as calling:

• rp_mobs.handle_fall_damage
• rp_mobs.handle_node_damage
• rp_mobs.handle_drowning

Must be called in on_step every step. mob is the mob. The dtime and moveresult arguments are the same as for on_step.

Task functions

This section contains the functions to create tasks, microtasks and task queues and to add them to the mob.

See also rp_mobs.init_tasks and rp_mobs.handle_tasks.

rp_mobs.create_task_queue(empty_decider, step_decider, start_decider)

Create a task queue object and returns it. The arguments are optional decider functions.

In these decider functions you can update the task queue by adding new tasks to it. Avoid complex and slow algorithms here!

• empty_decider(task_queue, mob): called when the task queue is empty
• step_decider(task_queue, mob, dtime): called at every server step
• start_decider(task_queue, mob): called right after the task queue starts

The function arguments are:

• task_queue: Reference to task queue on which the decider is run on. You can modify it at will.
• mob: Reference to mob object
• dtime: Time in seconds the last time the step decider was called (from on_step)

If decider argument is nil, nothing will be done for that event.

rp_mobs.create_task(def)

Create a task according to the specified def table. See the data structure above for the possible table fields.

Returns the task.

rp_mobs.create_microtask(def)

Create a microtask according to the specified def table. See the data structure above for the possible table fields. The statedata field will always be initialized as an empty table.

Returns the microtask.

Note this only creates it in memory. To actually execute it, you have to add it to a task with rp_mobs.add_microtask_to_task and then execute the task.

rp_mobs.add_task_queue(mob, task_queue)

Add a task queue to the given mob.

rp_mobs.add_task_to_task_queue(task, task_queue)

Add a task task to the given task queue object. Will also initialize the task_queue field of task.

rp_mobs.add_microtask_to_task(mob, microtask, task)

Add the microtask microtask to the specified task. Will also initialize the task field of microtask.

rp_mobs.end_current_task_in_task_queue(mob, task_queue)

Ends the currently active task in the given task_queue of mob. If the task queue is empty, nothing happens.

rp_mobs.clear_task_queue(mob, task_queue)

Remove all tasks in the given task_queue.

Task template functions

This mod comes with a number of template functions for common microtasks like walking. See API_TEMPLATES.md for a reference.

Breeding functions

rp_mobs.feed_tame_breed(mob, feeder, allowed_foods, food_till_tamed, food_till_horny, add_child_grow_timer, effect, eat_sound)

Requires the Breeding subsystem.

Let the player feeder feed the mob with their wielded item and optionally cause the mob to become tame and become horny. Should be called in on_rightclick.

• mob: The mob that is fed
• feeder: Player who feeds the mob
• allowed_foods: List of allowed food items, where each entry must be a table with these fields:
  • name: item name of food item
  • points optional food points to add to mob when eaten, defaults to _rp_hunger_food of item definition, and if that one is nil, too, defaults to 1
• food_till_tamed: How many food points the mob needs until it is tamed (if nil, can't be tamed by food)
• food_till_horny: How many food points the adult mob needs until it becomes horny (if nil, can't be made horny by food)
• add_child_growth_timer: (optional) If mob is a child, by how many seconds the child growth timer is increased (default: 20)
• effect: (optional) true to show particle effects, false otherwise (default: true)
• eat_sound: (optional) Name of sound to play (default: "mobs_eat")

rp_mobs.make_horny(mob, force)

Make mob horny, if possible.

rp_mobs.make_unhorny(mob)

Disable mob being horny.

Children functions

These function handle the child/adult status of the mob.

rp_mobs.turn_into_adult(mob)

Turns the mob into an adult.

rp_mobs.turn_into_child(mob)

Turns the mob into a child. IMPORTANT: You must check whether the mob has the "child_exists" tag before calling this. Don't call this function if the mob does not have this tag.

rp_mobs.advance_child_growth(mob, dtime)

Advance the child growth timer of the given mob by dtime (in seconds) and turn it into an adult once the time has passed. Should be added into the on_step function of the mob if you want children to grow up. If children must not grow up automatically, don't add this function.

Capturing functions

rp_mobs.attempt_capture = function(mob, capturer, capture_chances, force_take, replace_with)

Attempt to capture mob by capturer (a player). This requires a mob to have a mob available as an item (see rp_mobs.register_mob_items), unless replace_with is set.

It is recommended to put this function in the _on_capture field of the mob’s entity definition.

A mob capture may or may not succeed. A mob capture succeeds if all of these are true:

1. The wielded item is in capture_chances
2. The random capture chance succeeds
3. The mob is tamed or force_take is true
4. The mob is not a child

If successful, capturer will get the mob in item form and it will wear out the wielded tool (exception: no wear in Creative Mode). capturer might receive a message. If the mob was horny, the mob will stop being horny.

The created mob item stores the internal mob state and HP so it will be restored when the mob is being placed again.

Parameters:

• mob: The mob to capture
• capturer: Player trying to capture
• capture_changes: Table defining which items can capture and their chance to capture:
  • key: itemname, e.g. "rp_mobs:net"
  • value: capture chance, specified as 1/value. e.g. value 5 is a 1/5 chance.
• force_take: (optional) If true, can capture non-tamed mob
• replace_with: (optional) Give this item instead of the registered mob item. If nil (default), gives the registered mob item.

rp_mobs.call_on_capture(mob, capture)

Handle the mob’s capturing logic by calling the _on_capture function of the mob’s entity definition. This function must exist.

It is recommended to put this into on_rightclick, if you want this mob to be capturable.

Animation functions

rp_mobs.set_animation(mob, animation_name, animation_speed)

Set the animation for the given mob. The animation name is set in the mob definition in _animations. The name must exist in this table.

• mob: Mob object
• animation_name: Name of the animation to play, as specified in mob definition
• animation_speed: (optional): Override the default frame speed of the animation

This function handles the animation internals for you. If you call this function with the same animation name and speed twice in a row, nothing happens; no unnecessary network traffic is generated. If you call the function twice in row with the same animation name but a different frame speed, only the animation speed is updated the animation does not restart. In all other cases, the animation is set and started from the beginning.

Sound functions

rp_mobs.mob_sound(mob, sound, keep_pitch)

Plays a sound for the given mob. The pitch will be slightly randomized. Child mobs have a 50% higher pitch.

• mob: Mob to play sound for
• sound: A SimpleSoundSpec
• keep_pitch: If true, pitch will not be randomized and not be affected by child status

rp_mobs.default_mob_sound(mob, default_sound, keep_pitch)

Plays a default mob sound for the given mob. Default sounds are specified in rp_mobs.register_mob. The pitch will be slightly randomized. Child mobs have a 50% higher pitch.

• mob: Mob to play sound for
• default_sound: Name of a default mob sound, like "damage"
• keep_pitch: If true, pitch will not be randomized and not be affected by child status

rp_mobs.default_hurt_sound(mob, keep_pitch)

Make a mob play its “hurt” sound. The pitch will be slightly randomized. Child mobs have a 50% higher pitch.

• mob: Mob to play sound for
• keep_pitch: If true, pitch will not be randomized and not be affected by child status

Event functions

rp_mobs.register_on_die(callback)

Registers a function callback(mob, killer) where mob is a mob reference and killer is an object reference to the mob killer (or nil if there's no killer).

The function callback will be called when a mob has entered the 'dying' state, i.e. lying on the side but not disappeared yet.

This is useful to trigger kill-related achievements but it could be used for other reasons.

NOTE: This function differs from on_death in the entity definition. This callback triggers when the mob enters the 'dying' state, while on_death triggers when the entity is being actually removed.

IMPORTANT: Due to the implementation details, on_death will not provide the correct killer argument.

Utility functions

rp_mobs.is_alive(mob)

Returns true if the given mob is alive, false otherwise. mob must be a mob.

rp_mobs.heal(mob, heal)

Adds heal HP to mob. heal must not be negative.

rp_mobs.damage(mob, damage, no_sound, damager)

Removes damage HP from mob, optionally playing the mob's "damage" sound. damage must not be negative. If the mob HP reaches 0, the mob dies. damager is an optional object that damaged the mob (used for Hunter achievement).

If no_sound is true, then no damage sound will be played.

It is recommended to damage a mob only with this function instead of calling mob:set_hp directly in order to ensure consistency across mobs.

rp_mobs.die(mob, killer)

Kill the mob by putting it into the 'dying' state. killer is an optional object that killed the mob (used for Hunter achievement).

See the section about the “Dying” subsystem for details.

rp_mobs.drop_death_items(mob, pos)

Make mob mob drop its death items at pos, as if it had died.

This does not kill the mob.

rp_mobs.spawn_mob_drop(pos, item)

Spawns an mob drop at pos. A mob drop is an item stack “dropped” by a mob, usually on death, but it may also be used on other events.

item is an itemstring or ItemStack

The difference from minetest.add_item is that it adds some random velocity so this is the recommended function to make a mob drop something.

rp_mobs.has_tag(mob, tag_name)

Returns true if mob has the given tag_name or false if not.

See rp_mobs.register_mob for for info about tags.

`rp_mobs.mobdef_has_tag(mob_name, tag_name)

Return true if the mob definition for the mob with the given mob_name exists and has a tag with the given tag_name. Returns false otherwise.

See rp_mobs.register_mob for for info about tags.

rp_mobs.scan_environment(mob, dtime, y_offset)

Call this function for a mob at every step in an on_step handler to regularly check for nodes nearby the mob, so that other functions don't have to call minetest.get_node over and over again.

After this function was called, the mob will have the following fields added which you can read from:

• _env_node: Node table of the node at the mob position.
• _env_node_floor: Same as _env_node, but for exactly 1 node below the mob position

These fields should only be read from, not written to.

Parameters:

• mob: Mob object
• dtime: dtime from on_step
• y_offset: Y offset of roughly the "center point" of the mob, relative to the mob position (get_pos())

rp_mobs.drag(mob, dtime, drag, drag_axes)

Slow mob down for the specified drag vector at the specified drag axes. The drag vector specifies on each axis how much the mob slows down.

This will call set_velocity directly.

Parameters:

• mob: Mob object
• dtime: dtime from on_step
• drag: Drag vector. Higher number = faster slowdown.
• drag_axes: List of axes to which apply drag for ("x", "y", "z"). Other axes will be ignored.

Appendix

Glossary

• Mob: Non-player entity with added capabilities
• Task queue: Sequence of tasks a mob will execute in order; can run in parallel
• Task: A sequence of microtasks a mob will execute in order; can’t run in parallel
• Microtask: A simple function a mob will execute every step until a goal condition is met
• Decider: A function that is called in order to determine what to do next in a task queue
• Subsystem: An implementation of core mob features; must be enabled with special functions
• Tag: A simple property that can be assigned to mobs. Used to categorize mobs
• Breed: Bringing two mobs of the same kind together with food to create a child mob
• Tame: A mob eventually becomes tame when it has been fed. Tame mobs behave differently

Why yet another Mob API?

If you know the Minetest community, you might have noticed there are a lot of Mob APIs around. So why introduce another one?

The reason is that I (Wuzzy) was dissatisfied with the current mod situation.

The mob mods that existed went into one of two extremes:

The one extreme is Mobs Redo, hardcoding a lot of features into the core mod, but this created unmaintainable spaghetti code, made it hard to actually customize the mobs apart from changing some parameters. This usually was also quite wasteful since mobs executed code they didn't need. Repixture previously used an ancient fork for Mobs Redo. But the upside of Mobs Redo was that it was very easy to add lots of new mobs, but they couldn't differ that much.

The other extreme is mobkit. This mod basically wanted to do away with all the hardcoded behavior and instead give the developer more freedom. This approach sounded good at first but the problem was that mobkit offered so little in useful features that you basically still had to start from (almost) zero to re-implement common features that the mod should have already given you. This defeats the point of an API. Other mods that looked promising disappointed me because they are very poorly documented, making them useless for productive development.

Since none of the available options were satisfying, I've finally decided to create my own mobs API, which should allow me to add a diverse set of mobs relatively easy.

I want to have a middle ground between offering many useful built-in features and flexibility. Performance and documentation are also very important.

How this mod aims to reach these goals

The core of this mod is the 'task queue' system. This system serves two purposes: First, to allow mobs to execute tasks in a certain order, one after another. This idea was directly inspired by 'The Sims'. In this game, the sims (the characters you control) also have queue of tasks. This should allow to add complex tasks that require multiple steps.

Second, and more importantly, mobs can have multiple task queues at once, each of which will be run in parallel. This was loosely inspired by multitasking of operating systems.

Parallelization helps greatly improve performance and flexibility, and it simplifies many complex things. For example, a mob can now continuously scan its surroundings for enemies while still moving around. The code for both tasks can be cleanly separated.

Another core concept in this mod is modularization. While this mod offers built-in high-level features such as drowning, fall damage, breeding and more, almost everything is optional. Features need to be explicitly enabled for a mob before they are used. So mobs can only use the features they need, which is again good for performance and flexibility.