ScreenFollow

Defined in: renderer/src/ScreenFollow.ts:97

Each frame, projects a world source through a camera and writes the resulting screen coord to this entity’s Transform.worldPosition.

The canonical “billboard” primitive: pair with a UISurface (or UIRoot) on a screen-space layer using positioning: "transform" to produce UI that tracks a target entity but stays axis-aligned and constant-size regardless of camera zoom or rotation — nameplates, health bars, damage numbers, interaction prompts.

class Nameplate extends Entity {
  constructor(private readonly target: Entity, private readonly camera: CameraEntity) {
    super();
  }
  setup() {
    this.add(new Transform());
    this.add(new ScreenFollow({
      target: this.target,
      camera: this.camera,
      offset: new Vec2(0, -40),      // 40 screen px above the target
    }));
    const panel = this.add(new UISurface({
      positioning: "transform",      // reads Transform.worldPosition
      anchor: Anchor.BottomCenter,   // pivot on the panel
    }));
    panel.text("Grunt-42", { fontSize: 11 });
  }
}

Extends

• Component

Constructors

Constructor

new ScreenFollow(opts?): ScreenFollow

Defined in: renderer/src/ScreenFollow.ts:105

Parameters

opts?

ScreenFollowOptions

Returns

ScreenFollow

Overrides

Component.constructor

Properties

entity

entity: Entity

Defined in: core/dist/index.d.ts:2716

Back-reference to the owning entity. Set by the engine when the component is added to an entity. Do not set manually.

Inherited from

Component.entity

---

restorePriority?

static optional restorePriority?: number

Defined in: core/dist/index.d.ts:2874

Snapshot restore order. On load, an entity’s components are re-added in ascending priority, so a component whose onAdd() reads a sibling can rely on lower-priority siblings being present and initialized. Undeclared = 100. Engine components reserve 0-99; game and addon components declare a value only when a sibling onAdd() dependency requires it. Equal priorities restore in save-time add order. Subclasses inherit their base class’s priority unless they declare their own.

Inherited from

Component.restorePriority

---

updatePriority?

static optional updatePriority?: number

Defined in: core/dist/index.d.ts:2889

Class-level default for updatePriority: every instance runs at this priority unless its own updatePriority is written. Undeclared = 0. Subclasses inherit their base class’s value unless they declare their own. Declare it on a component whose behavior depends on running after (or before) a sibling, so the entity that adds it does not have to control the add order.

class BoundsClamp extends Component {
  static updatePriority = 10; // after the follow that moves the camera
}

Inherited from

Component.updatePriority

Accessors

context

Get Signature

get context(): EngineContext

Defined in: core/dist/index.d.ts:2770

Access the EngineContext from the entity’s scene. Throws if the entity is not in a scene.

Returns

EngineContext

Inherited from

Component.context

---

effectiveEnabled

Get Signature

get effectiveEnabled(): boolean

Defined in: core/dist/index.d.ts:2740

Whether the component is actually running: enabled, on an active entity, and past onAdd. This is the state onEnable and onDisable track — read it when a method has to behave one way live and another way dormant.

Returns

boolean

Inherited from

Component.effectiveEnabled

---

enabled

Get Signature

get enabled(): boolean

Defined in: core/dist/index.d.ts:2732

Whether this component runs. Disabled components are skipped by ComponentUpdateSystem.

Writing this fires onEnable / onDisable when the effective state changes — enabled && entity.isActive. A component disabled here stays disabled through a setActive(false) / setActive(true) cycle on its entity.

Returns

boolean

Set Signature

set enabled(value): void

Defined in: core/dist/index.d.ts:2733

Parameters

value

boolean

Returns

void

Inherited from

Component.enabled

---

scene

Get Signature

get scene(): Scene

Defined in: core/dist/index.d.ts:2765

Access the entity’s scene. Throws if the entity is not in a scene. Prefer this over threading through this.entity.scene in component code.

Returns

Scene

Inherited from

Component.scene

---

updatePriority

Get Signature

get updatePriority(): number

Defined in: core/dist/index.d.ts:2758

Where this component runs among its siblings. ComponentUpdateSystem calls update / fixedUpdate on an entity’s components in ascending priority; equal priorities run in add order. Undeclared = 0, so a negative value runs before siblings that keep the default and a positive value runs after them. Writable at any time, before or after add(). Defaults to the class’s static updatePriority.

class Player extends Entity {
  setup() {
    this.add(new Mover());
    this.add(new Brain()).updatePriority = -1; // decides before Mover moves
  }
}

Returns

number

Set Signature

set updatePriority(value): void

Defined in: core/dist/index.d.ts:2759

Parameters

value

number

Returns

void

Inherited from

Component.updatePriority

Methods

_applyEnabled()

_applyEnabled(effective): void

Defined in: core/dist/index.d.ts:2824

Internal

Force an effective-enabled transition, firing the hook on a flip. Used by Entity for teardown, where enabled and the entity’s activeness both still read true.

Parameters

effective

boolean

Returns

void

Inherited from

Component._applyEnabled

---

_refreshEnabled()

_refreshEnabled(): void

Defined in: core/dist/index.d.ts:2817

Internal

Recompute effective enabled-ness from enabled and the entity’s activeness, firing the hook on a flip.

Returns

void

Inherited from

Component._refreshEnabled

---

_runCleanups()

_runCleanups(): void

Defined in: core/dist/index.d.ts:2811

Internal

Run and clear all registered cleanups. Called by Entity.remove() and Entity._performDestroy() before onRemove/onDestroy.

Returns

void

Inherited from

Component._runCleanups

---

addCleanup()

protected addCleanup(fn): void

Defined in: core/dist/index.d.ts:2805

Register a cleanup function to run when this component is removed or destroyed.

Parameters

fn

() => void

Returns

void

Inherited from

Component.addCleanup

---

afterRestore()

afterRestore(_data, resolve): void

Defined in: renderer/src/ScreenFollow.ts:182

Called after onAdd() during save/load restoration. Apply state that depends on onAdd() having run.

Parameters

_data

unknown

resolve

SnapshotResolver

Returns

void

Overrides

Component.afterRestore

---

fixedUpdate()?

optional fixedUpdate(dt): void

Defined in: core/dist/index.d.ts:2863

Called every fixed timestep by the built-in ComponentUpdateSystem.

Parameters

dt

number

Fixed timestep in seconds, scaled by scene and entity timeScale.

Returns

void

Inherited from

Component.fixedUpdate

---

listen()

protected listen<T>(entity, token, handler): void

Defined in: core/dist/index.d.ts:2797

Subscribe to events on any entity, auto-unsubscribe on removal.

Type Parameters

T

T

Parameters

entity

Entity

token

EventToken<T>

handler

(data) => void

Returns

void

Inherited from

Component.listen

---

listenScene()

protected listenScene<T>(token, handler): void

Defined in: core/dist/index.d.ts:2803

Subscribe to scene-level events, auto-unsubscribe on removal. Handlers fire for bubbled entity events (entity = source) and scene.emit events (entity = undefined).

Type Parameters

T

T

Parameters

token

EventToken<T>

handler

(data, entity?) => void

Returns

void

Inherited from

Component.listenScene

---

onAdd()?

optional onAdd(): void

Defined in: core/dist/index.d.ts:2832

Called when the component is added to an entity. Validate dependencies here — a service, a sibling component, a render layer — and throw when one is missing. The throw is attributed to this component, recorded in Inspector.getErrors().callbackErrors, and rethrown, so it reaches the caller of entity.add() unchanged.

Returns

void

Inherited from

Component.onAdd

---

onDestroy()?

optional onDestroy(): void

Defined in: core/dist/index.d.ts:2853

Called when the component is destroyed (entity destroyed or component removed).

Returns

void

Inherited from

Component.onDestroy

---

onDisable()?

optional onDisable(): void

Defined in: core/dist/index.d.ts:2849

Called when the component stops being effectively enabled — enabled went false, the entity (or an ancestor) was deactivated, or the component is being removed or destroyed. Put live resources to sleep here; the component is reused afterwards, so do not free anything onEnable cannot rebuild.

Returns

void

Inherited from

Component.onDisable

---

onEnable()?

optional onEnable(): void

Defined in: core/dist/index.d.ts:2841

Called when the component becomes effectively enabled — enabled is true and the entity is active. Fires right after onAdd() for a component added to an active entity, and again on every later flip. Bring live resources back online here (unpause a sound, show a display object, re-enable a physics body). Game-state reset does not belong here: the hook sees whatever state the component held while dormant.

Returns

void

Inherited from

Component.onEnable

---

onRemove()?

optional onRemove(): void

Defined in: core/dist/index.d.ts:2851

Called when the component is removed from an entity.

Returns

void

Inherited from

Component.onRemove

---

serialize()

serialize(): ScreenFollowData | null

Defined in: renderer/src/ScreenFollow.ts:149

Return a JSON-serializable snapshot of this component’s state. Used by the save system.

Returns

ScreenFollowData | null

Overrides

Component.serialize

---

service()

protected service<T>(key): T

Defined in: core/dist/index.d.ts:2787

Lazy proxy-based service resolution. Can be used at field-declaration time:

readonly input = this.service(InputManagerKey);

The actual resolution is deferred until first property access.

Type Parameters

T

T extends object

Parameters

key

ServiceKey<T>

Returns

T

Inherited from

Component.service

---

sibling()

protected sibling<C>(cls): C

Defined in: core/dist/index.d.ts:2795

Lazy proxy-based sibling component resolution. Can be used at field-declaration time:

readonly anim = this.sibling(AnimatedSpriteComponent);

The actual resolution is deferred until first property access.

Type Parameters

C

C extends Component

Parameters

cls

ComponentClass<C>

Returns

C

Inherited from

Component.sibling

---

update()

update(): void

Defined in: renderer/src/ScreenFollow.ts:115

Called every frame by the built-in ComponentUpdateSystem.

Returns

void

Overrides

Component.update

---

use()

protected use<T>(key): T

Defined in: core/dist/index.d.ts:2778

Resolve a service by key, cached after first lookup. Scene-scoped values (registered via scene._registerScoped) take precedence over engine scope. A key declared with scope: "scene" that falls back to engine scope emits a one-shot dev warning — almost always signals a missed beforeEnter hook.

Type Parameters

T

T

Parameters

key

ServiceKey<T>

Returns

T

Inherited from

Component.use

---

fromSnapshot()

static fromSnapshot(data): ScreenFollow

Defined in: renderer/src/ScreenFollow.ts:169

Parameters

data

ScreenFollowData

Returns

ScreenFollow