How to remove components that support multiples?

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!

Python user? Check out the Python port of this library, ecstremity!

usage and examples

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:

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 `Position`
// and `Velocity` component but not a `IsFrozen` component. A query can
// have any combination of `all`, `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);

Engine

The Engine class is used to register all components and prefabs, and create new Worlds.

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

World

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.

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 ID
getEntity(id): get an Entity by ID
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 entity.destroy()
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

Entity

A unique id and a collection of components.

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 destroyed
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 true 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

Component

Components hold entity data. A component must be defined and then registered with the Engine. This example defines a simple Health component:

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 fired
    // on the entity: `entity.fireEvent('damage-taken', { damage: 12 })`
    // the `camelcase` library is used to map event names to methods
    onDamageTaken(evt) {
        // event `data` 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.
static keyProperty = null what property should be used as the key for accessing this component. if allowMultiple is false, this has no effect. If this property is omitted, it will be stored as an array on the component.
entity returns the Entity this component is attached to
world returns the World this component is in
isDestroyed returns true 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](evt) add these methods to capture the specific event

This example shows how allowMultiple and keyProperty work:

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 `2`
player.impulse[2];
// returns `true` 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 automatically
// set the `rightHand.item` property to `null`
player.equipmentSlot.rightHand.item.destroy();

// remove and destroy the `rightHand` equipment slot
player.equipmentSlot.rightHand.destroy();

Query

Queries keep track of sets of entities defined by component types. They are limited to the world they're created in.

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.

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!

serialization

example Save game state by serializing all entities and components

const saveGame = () => {
    const data = world.serialize();
    localStorage.setItem('savegame', data);
};

...

const loadGame = () => {
    const data = localStorage.getItem('savegame');
    world.deserialize(data);
};

Event

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.

// a `Health` component which listens for a `take damage` event
class Health extends Component {
    ...
    // event names are mapped to methods using the `camelcase` library.
    onTakeDamage(evt) {
        console.log(evt);
        this.value -= evt.data.amount;

        // the event gets passed to all components the `entity` unless a component
        // invokes `evt.prevent()` 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?
console.log(evt.prevented);  // was `prevent()` or `handle()` called?
console.log(evt.handle()); // handle and prevent the event from continuing
console.log(evt.prevent()); // prevent the event from continuing without marking `handled`
console.log(evt.is('take-damage')); // simple name check

Prefab

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.

// 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,
    },
});

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