Entities

Introduction

An entity by itself has no behavior or appearance; it simply acts as a container to which components can be attached.

Creating an Entity

The following code shows how to create a new entity without any components

Example

import * as ecs from '@8thwall/ecs'

const eid = world.createEntity()

Deleting an Entity

The following code shows how to delete an existing entity given its id:

Example

import * as ecs from '@8thwall/ecs'

world.deleteEntity(eid)

Adding Components to an Entity

The following code shows how to add a built-in component to an entity at runtime.

Example

const box = world.createEntity()

ecs.BoxGeometry.set(world, box, {
    width: 1,
    height: 1,
    depth: 1,
})

ecs.Material.set(world, box, {
    r: 255,
    g: 255,
    b: 255,
})

Create and Modify Relationships

The following code shows how you can use built-in helper methods to create or change relationships between entities.

Example

// Entities are automatically a child of World.
const foo = world.createEntity()
const bar = world.createEntity()

// Set foo to be a child of bar.
world.setParent(foo, bar)

// Get the parent of bar. (returns an eid where <= 0 is undefined)
world.getParent(bar)

// Get the children of foo. (returns a Generator)
world.getChildren(foo)

Helper Functions

There are a number of helper functions for interacting with an entity's transform.

tip

Entities are positioned relative to their parent. The getWorldTransform() function retrieves the object’s transform in world space, accounting for all parent transforms.

world.setScale(eid, 1, 1, 1)
world.setPosition(eid, 1, 1, 1)
world.setQuaternion(eid, 0, 0, 0, 1)
world.normalizeQuaternion(eid)

const tempMatrix = ecs.math.mat4.i()
world.getWorldTransform(eid1, tempMatrix)

world.setTransform(eid2, tempMatrix)