Repixture/mods/rp_mobs/API.md

Repixture Mobs API

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

Core concepts

Mobs

In this mod, a "mob" refers a non-player entity with added capabilities like physics and 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".

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 decider function which is called every time the task queue is empty.

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

Physical forces and the mob's desired movements are separated. Physical forces like gravity always affect the mob, no matter where it actually wants to move (if at all). On top of physics, mobs have a desired movement.

So instead of setting the entity acceleration and velocity directly, you're supposed to set the physical forces and desired mob movements as vectors; this mod will then do the final calculation step for you.

To use the physics system, you must initialize it first by calling rp_mobs.init_physics in on_activate and then let this mob handle the physics for you in rp_mobs_handle_physics in on_step. You also must never call builtin functions set_velocity and set_acceleration directly; you only change vectors.

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.

You can use the following template:

rp_mobs.register_mob("MOBNAME", {
	description = "MOB DESCRIPTION",
	drops = { ADD_YOUR_DROPS_HERE },
	entity_definition = {
		on_activate = function(self, staticdata)
			rp_mobs.restore_state(self, staticdata)
			rp_mobs.init_physics(self)
			rp_mobs.init_tasks(self)
		end,
		on_step = function(self, dtime, moveresult)
			rp_mobs.handle_physics(self)
			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. You can optionally define this field:

• label: Brief string explaining what the task does. Only for debug

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
• on_finished: Return true if the microtask is complete, false otherwise
• 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 succeeds (default: false)
• statedata: Table containing data that can be modified and read at runtime

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

on_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 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 mob physics and tasks are also subsystems

Each subsystem can be enabled by adding a handle_* function in on_step and most of the time, also an init_* function in on_activate.

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.

The Tasks and Physics subsystems are mandatory and must be enabled for all mobs.

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
------------+--------------------------+----------------------------
Physics*    | rp_mobs.init_physics     | rp_mobs.handle_physics
Tasks*      | rp_mobs.init_tasks       | rp_mobs.handle_tasks
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 init function required
*** = can be replaced with rp_mobs.handle_environment_damage

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 drowning 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.

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

• _cmi_is_mob: Always true. Indicates the entity is a mob. Do not touch
• _dying: Is true when mob is currently dying and about to be removed
• _tamed: true if mob is tame
• _tb_level: tame/breed level. Starts at 0 and increases for any food given, used to trigger taming/breeding
• _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
• _pregnant: true if mob is pregnant and about to spawn a child

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.
• _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.

• _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

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: Short mob name used for display purposes
• drops: Table of itemstrings to be dropped when the mob dies as an adult (default: empty table)
• child_drops: Table of itemstrings to be dropped when the mob dies as a child (default: empty table)
• 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 damage
  • eat: When mob eats (not yet implemented)
  • call: Occassional mob call (only played manually)
• entity_definition: Entity definition table. It may 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
• 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

rp_mobs.register_mob_item(mobname, invimg, desc)

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.

• mobname: Mob identifier
• invimg: Inventory image texture
• desc: Description for inventory

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)

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 must 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.

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 or physics.

Calling rp_mobs.restore_state in on_activate is a requirement, but everything else is optional depending on your needs.

For example, you can choose to not call rp_mobs.init_physics if your mob does not need the physics subsystem.

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.

rp_mobs.init_physics(mob)

Initialize and enable the mob physics system for mob mob. This is supposed to go into on_activate of the entity definition. This function must be called before any other physics-related function.

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 function must be called before any other task-related function is called.

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)

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.

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

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 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_physics(mob)

Update the mob physics for a single mob step. Required for the mob physics to work. This is supposed to go into on_step of the entity definition. It must be called every step.

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 in nodes with a non-zero damage_per_second.

In the current implementation, only the mob position is checked, other nodes are ignored. This behavior may change in the future.

Checks if the mob is standing in a damaging node and if yes, damage it. Otherwise, no damage will be taken.

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 should 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(decider)

Create a task queue object and returns it. decider is an optional function with signature decider(task_queue, mob) that is called whenever the task queue is empty. In this function you can update the task queue by adding new tasks to it. Avoid complex and slow algorithms here!

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.

rp_mobs.add_microtask_to_task(mob, microtask, task)

Add the microtask microtask to the specified task.

Physics functions

These functions require the Physics subsystem.

rp_mobs.add_phys_acceleration(mob, name, vector)

Add a named vector to the mob's physical acceleration. The mob's physical acceleration is the sum of all named acceleration vectors.

If the named vector already exists, it will be overwritten.

• mob: The mob
• name: Name of the acceleration vector
• vector: The acceleration vector

rp_mobs.remove_phys_acceleration(mob, name)

Remove a named vector to the mob's physical acceleration that has been added with rp_mobs.add_phys_acceleration before.

• mob: The mob
• name: Name of the acceleration vector to remove

rp_mobs.add_phys_velocity(mob, name, vector)

Add a named vector to the mob's physical velocity. The mob's physical velocity is the sum of all named velocity vectors.

This function is analogous to rp_mobs.add_phys_acceleration.

rp_mobs.remove_phys_velocity(mob, name)

Same as rp_mobs.remove_phys_acceleration, but for velocity.

rp_mobs.activate_gravity(mob)

Activate gravity for mob.

rp_mobs.deactivate_gravity(mob)

Deactivate gravity for mob.

Breeding functions

rp_mobs.feed_tame_breed(mob, feeder, allowed_foods, food_till_tamed, can_breed, 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
• food_till_tamed: How many food points the mob needs until it is tamed
• can_breed: true if feeding may cause this mob to become horny, false otherwise
• 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.

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)

Requires the Capturing subsystem.

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

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.

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)

Requires the Capturing subsystem.

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

Achievement function

This section is for manually triggering the built-in achievement(s) of this mod.

rp_mobs.check_and_trigger_hunter_achievement(mob, killer)

Checks if the mob is an animal and has a food item in its drop table and if yes, will award the “Hunter” achievement to killer if killer is a player.

This is called in the default death handler (rp_mobs.on_death_default) so by default, you don’t need to call this yourself. But if you a custom death handler for on_death, it is recommended to call this function for animals.

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)

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.

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.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.

Appendix

Glossary

• Mob: Non-player entity with added capabilities and a task queue
• 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 when the task queue is empty in order to generate new tasks
• Subsystem: A built-in mob behavior (physics, breeding, drowning)