entity-component-system
npm install geotic#### geotic
_adjective_ physically concerning land or its inhabitants.
Geotic is an ECS library focused on performance, features, and non-intrusive design. Geotic is consistantly one of the fastest js ecs libraries, especially when it comes to large numbers of entities and queries.
- entity a unique id and a collection of components
- component a data container
- query a way to gather collections of entities that match some criteria, for use in systems
- world a container for entities and queries
- prefab a template of components to define entities as JSON
- event a message to an entity and it's components
This library is _heavily_ inspired by ECS in _Caves of Qud_. Watch these talks to get inspired!
- Thomas Biskup - There be dragons: Entity Component Systems for Roguelikes
- Brian Bucklew - AI in Qud and Sproggiwood
- Brian Bucklew - Data-Driven Engines of Qud and Sproggiwood
Python user? Check out the Python port of this library, ecstremity!
```
npm install geotic
- Sleepy Crawler a full fledged roguelike that makes heavy use of geotic by @ddmills
- snail6 a bloody roguelike by @luetkemj
- Gobs O' Goblins by @luetkemj
- Javascript Roguelike Tutorial by @luetkemj
- basic example using pixijs
Below is a contrived example which shows the basics of geotic:
`js
import { Engine, Component } from 'geotic';
// define some simple components
class Position extends Component {
static properties {
x: 0,
y: 0,
};
}
class Velocity extends Component {
static properties {
x: 0,
y: 0,
};
}
class IsFrozen extends Component {}
const engine = new Engine();
// all Components and Prefabs must be registered by the engine
engine.registerComponent(Position);
engine.registerComponent(Velocity);
engine.registerComponent(IsFrozen);
...
// create a world to hold and create entities and queries
const world = engine.createWorld();
// Create an empty entity. Call entity.id to get the unique ID.
const entity = world.createEntity();
// add some components to the entity
entity.addComponent(Position, { x: 4, y: 10 });
entity.addComponent(Velocity, { x: 1, y: .25 });
// create a query that tracks all components that have both a PositionVelocity
// and component but not a IsFrozen component. A query canall
// have any combination of , none and any
const kinematics = world.createQuery({
all: [Position, Velocity],
none: [IsFrozen]
});
...
// geotic does not dictate how your game loop should behave
const loop = (dt) => {
// loop over the result set to update the position for all entities
// in the query. The query will always return an up-to-date array
// containing entities that match
kinematics.get().forEach((entity) => {
entity.position.x += entity.velocity.x * dt;
entity.position.y += entity.velocity.y * dt;
});
};
...
// serialize all world entities into a JS object
const data = world.serialize();
...
// convert the serialized data back into entities and components
world.deserialize(data);
`
The Engine class is used to register all components and prefabs, and create new Worlds.
`js
import { Engine } from 'geotic';
const engine = new Engine();
engine.registerComponent(clazz);
engine.registerPrefab({ ... });
engine.destroyWorld(world);
`
Engine properties and methods:
- registerComponent(clazz): register a Component so it can be used by entities
- regsterPrefab(data): register a Prefab to create pre-defined entities
- destroyWorld(world): destroy a world instance
The World class is a container for entities. Usually only one instance is needed,
but it can be useful to spin up more for offscreen work.
`js
import { Engine } from 'geotic';
const engine = new Engine();
const world = engine.createWorld();
// create/destroy entities
world.createEntity();
world.getEntity(entityId);
world.getEntities();
world.destroyEntity(entityId);
world.destroyEntities();
// create queries
world.createQuery({ ... });
// create entity from prefab
world.createPrefab('PrefabName', { ... });
// serialize/deserialize entities
world.serialize();
world.serialize(entities);
world.deserialize(data);
// create an entity with a new ID and identical components & properties
world.cloneEntity(entity);
// generate unique entity id
world.createId();
// destroy all entities and queries
world.destroy();
`
World properties and methods:
- createEntity(id = null): create an Entity. optionally provide an IDEntity
- getEntity(id): get an by IDentity.destroy()
- getEntities(): get _all_ entities in this world
- createPrefab(name, properties = {}): create an entity from the registered prefab
- destroyEntity(entity): destroys an entity. functionally equivilant to
- destroyEntities(): destroys all entities in this world instance
- serialize(entities = null): serialize and return all entity data into an object. optionally specify a list of entities to serialize
- deserialize(data): deserialize an object
- cloneEntity(entity): clone an entity
- createId(): Generates a unique ID
- destroy(): destroy all entities and queries in the world
A unique id and a collection of components.
`js
const zombie = world.createEntity();
zombie.add(Name, { value: 'Donnie' });
zombie.add(Position, { x: 2, y: 0, z: 3 });
zombie.add(Velocity, { x: 0, y: 0, z: 1 });
zombie.add(Health, { value: 200 });
zombie.add(Enemy);
zombie.name.value = 'George';
zombie.velocity.x += 12;
zombie.fireEvent('hit', { damage: 12 });
if (zombie.health.value <= 0) {
zombie.destroy();
}
`
Entity properties and methods:
- id: the entities' unique id
- world: the geotic World instance
- isDestroyed: returns true if this entity is destroyedtrue
- components: all component instances attached to this entity
- add(ComponentClazz, props={}): create and add the registered component to the entity
- has(ComponentClazz): returns true if the entity has component
- owns(component): returns if the specified component belongs to this entity
- remove(component): remove the component from the entity and destroy it
- destroy(): destroy the entity and all of it's components
- serialize(): serialize this entity and it's components
- clone(): returns an new entity with a new unique ID and identical components & properties
- fireEvent(name, data={}): send an event to all components on the entity
Components hold entity data. A component must be defined and then registered with the Engine. This example defines a simple Health component:
`js
import { Component } from 'geotic';
class Health extends Component {
// these props are defaulting to 10
// anything defined here will be serialized
static properties {
current: 10,
maximum: 10,
};
// arbitrary helper methods and properties can be declared on
// components. Note that these will NOT be serialized
get isAlive() {
return this.current > 0;
}
reduce(amount) {
this.current = Math.max(this.current - amount, 0);
}
heal(amount) {
this.current = Math.min(this.current + amount, this.maximum);
}
// This is automatically invoked when a damage-taken event is firedentity.fireEvent('damage-taken', { damage: 12 })
// on the entity: camelcase
// the library is used to map event names to methodsdata
onDamageTaken(evt) {
// event is an arbitray object passed as the second parameter
// to entity.fireEvent(...)
this.reduce(evt.data.damage);
// handling the event will prevent it from continuing
// to any other components on the entity
evt.handle();
}
}
`
Component properties and methods:
- static properties = {} object that defines the properties of the component. Properties must be json serializable and de-serializable!
- static allowMultiple = false are multiple of this component type allowed? If true, components will either be stored as an object or array on the entity, depending on keyProperty.allowMultiple
- static keyProperty = null what property should be used as the key for accessing this component. if is false, this has no effect. If this property is omitted, it will be stored as an array on the component.true
- entity returns the Entity this component is attached to
- world returns the World this component is in
- isDestroyed returns if this component is destroyed
- serialize() serialize the component properties
- destroy() remove this and destroy this component
- onAttached() override this method to add behavior when this component is attached (added) to an entity
- onDestroyed() override this method to add behavior when this component is removed & destroyed
- onEvent(evt) override this method to capture all events coming to this component
- on\EventName\ add these methods to capture the specific event
This example shows how allowMultiple and keyProperty work:
`js
class Impulse extends Component {
static properties = {
x: 0,
y: 0,
};
static allowMultiple = true;
}
ecs.registerComponent(Impulse);
...
// add multiple Impulse components to the player
player.add(Impulse, { x: 3, y: 2 });
player.add(Impulse, { x: 1, y: 0 });
player.add(Impulse, { x: 5, y: 6 });
...
// returns the array of Impulse components
player.impulse;
// returns the Impulse at position 2true
player.impulse[2];
// returns if the component has an Impulse component
player.has(Impulse);
// the player.impulse property is an array
player.impulse.forEach((impulse) => {
console.log(impulse.x, impulse.y);
});
// remove and destroy the first impulse
player.impulse[0].destroy();
...
class EquipmentSlot extends Component {
static properties = {
name: 'hand',
itemId: 0,
};
static allowMultiple = true;
static keyProperty = 'name';
get item() {
return this.world.getEntity(this.itemId);
}
set item(entity) {
return this.itemId = entity.id;
}
}
ecs.registerComponent(EquipmentSlot);
...
const player = ecs.createEntity();
const helmet = ecs.createEntity();
const sword = ecs.createEntity();
// add multiple equipment slot components to the player
player.add(EquipmentSlot, { name: 'rightHand' });
player.add(EquipmentSlot, { name: 'leftHand', itemId: sword.id });
player.add(EquipmentSlot, { name: 'head', itemId: helmet.id });
...
// since the EquipmentSlot had a keyProperty=name, the name
// is used to access them
player.equipmentSlot.head;
player.equipmentSlot.rightHand;
// this will destroy the sword entity and automaticallyrightHand.item
// set the property to null
player.equipmentSlot.rightHand.item.destroy();
// remove and destroy the rightHand equipment slot
player.equipmentSlot.rightHand.destroy();
`
Queries keep track of sets of entities defined by component types. They are limited to the world they're created in.
`js
const query = world.createQuery({
any: [A, B], // exclude any entity that does not have at least one of A OR B.
all: [C, D], // exclude entities that don't have both C AND D
none: [E, F], // exclude entities that have E OR F
});
query.get().forEach((entity) => ...); // loop over the latest set (array) of entites that match
// alternatively, listen for when an individual entity is created/updated that matches
query.onEntityAdded((entity) => {
console.log('an entity was updated or created that matches the query!', entity);
});
query.onEntityRemoved((entity) => {
console.log('an entity was updated or destroyed that previously matched the query!', entity);
});
`
- query.get() get the result array of the query. This array should not be modified in place. For performance reasons, the result array that is exposed is the working internal query array.
- onEntityAdded(fn) add a callback for when an entity is created or updated to match the query
- onEntityRemoved(fn) add a callback for when an entity is removed or updated to no longer match the query
- has(entity) returns true if the given entity is being tracked by the query. Mostly used internally
- refresh() re-check all entities to see if they match. Very expensive, and only used internally
#### Performance enhancement
Set the immutableResults option to false if you are not modifying the result set. This option defaults to true. WARNING: When this option is set to false, strange behaviour can occur if you modify the results. See issue #55.
`js
const query = world.createQuery({
all: [A, B],
immutableResult: false, // defaults to TRUE
});
const results = query.get();
results.splice(0, 1); // DANGER! do not modify results if immutableResult is false!
`
example Save game state by serializing all entities and components
`js
const saveGame = () => {
const data = world.serialize();
localStorage.setItem('savegame', data);
};
...
const loadGame = () => {
const data = localStorage.getItem('savegame');
world.deserialize(data);
};
`
Events are used to send a message to all components on an entity. Components can attach data to the event and prevent it from continuing to other entities.
The geotic event system is modelled aver this talk by Brian Bucklew - AI in Qud and Sproggiwood.
`jsHealth
// a component which listens for a take damage eventcamelcase
class Health extends Component {
...
// event names are mapped to methods using the library.
onTakeDamage(evt) {
console.log(evt);
this.value -= evt.data.amount;
// the event gets passed to all components the entity unless a componentevt.prevent()
// invokes or evt.handle()
evt.handle();
}
// watch ALL events coming to component
onEvent(evt) {
console.log(evt.name);
console.log(evt.is('take-damage'));
}
}
...
entity.add(Health);
const evt = entity.fireEvent('take-damage', { amount: 12 });
console.log(evt.name); // return the name of the event. "take-damage"
console.log(evt.data); // return the arbitrary data object attached. { amount: 12 }
console.log(evt.handled); // was handle() called?prevent()
console.log(evt.prevented); // was or handle() called?handled
console.log(evt.handle()); // handle and prevent the event from continuing
console.log(evt.prevent()); // prevent the event from continuing without marking
console.log(evt.is('take-damage')); // simple name check
`
Prefabs are a pre-defined template of components.
The prefab system is modelled after this talk by Thomas Biskup - There be dragons: Entity Component Systems for Roguelikes.
`js
// prefabs must be registered before they can be instantiated
engine.registerPrefab({
name: 'Being',
components: [
{
type: 'Position',
properties: {
x: 4,
y: 10,
},
},
{
type: 'Material',
properties: {
name: 'flesh',
},
},
],
});
ecs.registerPrefab({
// name used when creating the prefab
name: 'HumanWarrior',
// an array of other prefabs of which this one derives. Note they must be registered in order.
inherit: ['Being', 'Warrior'],
// an array of components to attach
components: [
{
// this should be a component constructor name
type: 'EquipmentSlot',
// what properties should be assigned to the component
properties: {
name: 'head',
},
},
{
// components that allow multiple can easily be added in
type: 'EquipmentSlot',
properties: {
name: 'legs',
},
},
{
type: 'Material',
// if a parent prefab already defines a Material component, this flag
// will say how to treat it. Defaults to overwrite=true
overwrite: true,
properties: {
name: 'silver',
},
},
],
});
...
const warrior1 = world.createPrefab('HumanWarrior');
// property overrides can be provided as the second argument
const warrior2 = world.createPrefab('HumanWarrior', {
equipmentSlot: {
head: {
itemId: world.createPrefab('Helmet').id
},
},
position: {
x: 12,
y: 24,
},
});
``