Entities

Entities is a library for the MiniScript language that implements Entity component system pattern.

Entities are mere IDs (eid).

Systems are any object that has an .update(dt, component, world) method.

Components are a map with a ._name property. Also it should implement a .set(property, value) method which is only invoked once using arguments "eid", eid when the component is assigned to an entity. It might be as simple as Comp.set = function(_, eid); self.eid = eid; end function, or you could subclass your component from entities.Class and get it for free (in this case each component should also set self._inited to true).

Component instances and systems are stored inside an entities.World object.

API

• World .init -- Initializes and returns a world.
• World .createEntity -- Returns ID (eid) of a new entity inside the world.
• World .setComponent(eid, component) -- Assigns a component to an entity.
• World .getComponent(eid, componentClass, default=null) -- Returns a component assigned to an entity. The componentClass argument may be either a map with the ._name property or a string with a component name. If there's no component of the given class, the default argument is returned.
• World .getComponents(eid) -- Returns a map of all components assigned to an entity.
• World .removeComponent(eid, componentClass) -- Removes a component of a given class from an entity. No-op if there's no such component.
• World .iterComponents(componentClass, callback) -- Invokes the callback argument on each component of a given class.
• World .addSystem(system, componentClass) -- Installs a system inside the world. On each world's update its .update(dt, component, world) method is invoked for all components of the given class.
• World .update(dt=null) -- Executes one frame of the world.

Example

import "entities"

world = (new entities.World).init

Mob = {}
Mob._name = "Mob"
Mob.eid = null
Mob.x = null
Mob.y = null
Mob.set = function(_, eid)
	self.eid = eid
end function
Mob.init = function(x, y)
	self.x = x
	self.y = y
	return self
end function

catID = world.createEntity
world.setComponent catID, (new Mob).init(42, 43)

dogID = world.createEntity
world.setComponent dogID, (new Mob).init(44, 45)

print world.getComponent(catID, Mob).x  // prints 42

SysMoveMobs = {}
SysMoveMobs.update = function(dt, comp, world)
	comp.x += 1
end function

world.addSystem SysMoveMobs, Mob

world.update

print world.getComponent(catID, Mob).x  // prints 43