Jecs

Jecs. Just an Entity Component System.

Members

World

jecs.World: World

A world is a container of all ECS data. Games can have multiple worlds but component IDs may conflict between worlds. Ensure to register the same component IDs in the same order for each world.

Wildcard

jecs.Wildcard: Id

Builtin component type. This ID is used for wildcard queries.

Component

jecs.Component: Id

Builtin component type. Every ID created with world:component() has this type added to it. This is meant for querying every component ID.

ChildOf

jecs.ChildOf: Id

Builtin component type. This ID is for creating parent-child hierarchies.

OnAdd

jecs.OnAdd: Id

Builtin component type. This ID is for setting up a callback that is invoked when an instance of a component is added.

OnRemove

jecs.OnRemove: Id

Builtin component type. This ID is for setting up a callback that is invoked when an instance of a component is removed.

OnChange

jecs.OnChange: Id

Builtin component type. This ID is for setting up a callback that is invoked when an instance of a component is changed.

Exclusive

jecs.Exclusive: Id

Builtin component type. This ID is for encoding that an ID is Exclusive meaning that an entity can never have more than one target for that exclusive relation.

luau

local ChildOf = world:entity()
world:add(ChildOf, jecs.Exclusive)

local pop = world:entity()
local dad = world:entity()
local kid = world:entity()

world:add(kid, pair(ChildOf, dad))
print(world:target(kid, ChildOf, 0) == dad)
world:add(kid, pair(ChildOf, pop))
print(world:target(kid, ChildOf, 1) == dad) -- If ChildOf was not exclusive this would have been true
print(world:target(kid, ChildOf, 0) == pop)

-- Output:
--  true
--  false
--  true

INFO

By default, jecs.ChildOf is already an exclusive relationship and this is just a demonstration of how to use it. In some cases you can use Exclusive relationships as a performance optimization as you can guarantee there will only be one target, therefore retrieving the data from a wildcard pair with that exclusive relationship can be deterministic.

Name

jecs.Name: Id

Builtin component type. This ID is for naming components, but realistically you could use any component to do that.

Rest

jecs.Rest: Id

Builtin component type. This ID is simply for denoting the end of the range for builtin component IDs.

Functions

pair()

function jecs.pair(
    first: Entity, -- The first element of the pair, referred to as the relationship of the relationship pair.
    object: Entity, -- The second element of the pair, referred to as the target of the relationship pair.
): number -- Returns the ID with those two elements

INFO

While relationship pairs can be used as components and have data associated with an ID, they cannot be used as entities. Meaning you cannot add components to a pair as the source of a binding.

pair_first()

function jecs.pair_first(
   	pair: Id, -- A full pair ID encoded using a relation-target pair.
): Entity -- The ID of the first element. Returns 0 if the ID is not alive.

Returns the first element (the relation part) of a pair ID.

Example:

local Likes = world:component()
local alice = world:entity()
local bob = world:entity()

local pair_id = pair(Likes, alice)
local relation = jecs.pair_first(pair_id)
print(relation == Likes) -- true

pair_second()

function jecs.pair_second(
   	pair: Id, -- A full pair ID encoded using a relation-target pair.
): Entity -- The ID of the second element. Returns 0 if the ID is not alive.

Returns the second element (the target part) of a pair ID.