BoxCollider2D

A rectangular 2D collider.

Type	Name	Interface Description
Variables	size: Vector2f	• Function: Gets or sets the authored size of the 2D box collider. This is the full width and height of the rectangular shape.
Functions	constructor()

Examples

constructor()

let obj = new APJS.BoxCollider2D();

Use Case

Example 1 — Play a sound effect when a 2D physics object collides — uses CollisionEvent2D.Enter on collider's object emitter

@component()
export class CollisionSoundEffect extends APJS.BasicScriptComponent {
  @serializeProperty
  sfxPlayer!: APJS.SceneObject;

  private sfxAudio!: APJS.AudioComponent;
  private collider!: APJS.BoxCollider2D;
  private initialized = false;
  private collisionCallback!: (event: APJS.IEvent) => void;

  onUpdate(dt: number): void {
    if (this.initialized) return;
    if (!this.sfxPlayer) return;

    this.sfxAudio = this.sfxPlayer.getComponent("AudioComponent") as APJS.AudioComponent;
    // Get any 2D collider on this object (BoxCollider2D or CircleCollider2D)
    this.collider = this.getSceneObject().getComponent("BoxCollider2D") as APJS.BoxCollider2D;
    if (!this.sfxAudio || !this.collider) return;

    // CRITICAL: enable collision events before registering listener
    this.collider.emitCollisionEvent = true;

    this.collisionCallback = (event: APJS.IEvent) => {
      // Play SFX on each collision
      this.sfxAudio.stop();
      this.sfxAudio.loopCount = 1;
      this.sfxAudio.play();
    };

    // Use object emitter on the COLLIDER (not global emitter)
    const emitter = APJS.EventManager.getObjectEmitter(this.collider);
    emitter.on(APJS.CollisionEvent2D.Enter, this.collisionCallback, this);
    this.initialized = true;
  }

  onDestroy(): void {
    if (this.collider && this.collisionCallback) {
      const emitter = APJS.EventManager.getObjectEmitter(this.collider);
      emitter.off(APJS.CollisionEvent2D.Enter, this.collisionCallback, this);
    }
  }
}

Example 2 — Detect 2D collision and reverse velocity to bounce off obstacles

@component()
export class CollisionBounce extends APJS.BasicScriptComponent {
  private collisionCallback: (event: APJS.IEvent) => void;
  private collider: APJS.BoxCollider2D;
  private velocity: APJS.Vector2f = new APJS.Vector2f(100, 100);
  private startVelocity: APJS.Vector2f = new APJS.Vector2f(100, 100);
  private startPos!: APJS.Vector2f;
  private startGravityOn = true;
  private rb!: APJS.RigidBody2D;
  private inited = false;

  // RecordStart: reset bouncing ball per Physics2D §"RecordStart Reset for 2D Physics"
  // (single-body block): velocity → script accumulators (this.velocity) → anchoredPosition
  // → useGravity. Listener wiring per GameState §"RecordStart / RecordEnd Lifecycle".
  private onRecordStart = (_event: APJS.IEvent) => {
    if (!this.inited) return;
    this.rb.velocity = new APJS.Vector2f(0, 0);
    this.velocity = new APJS.Vector2f(this.startVelocity.x, this.startVelocity.y);
    const obj = this.getSceneObject();
    const st = obj.getComponent("ScreenTransform") as APJS.ScreenTransform;
    if (st && this.startPos) {
      st.anchoredPosition = new APJS.Vector2f(this.startPos.x, this.startPos.y);
    }
    this.rb.useGravity = this.startGravityOn;
  };

  onStart(): void {
    this.collider = this.getSceneObject().getComponent("BoxCollider2D") as APJS.BoxCollider2D;
    if (!this.collider) return;

    this.collider.emitCollisionEvent = true;

    this.collisionCallback = (event: APJS.IEvent) => {
      const infos = event.args[0] as APJS.CollisionInfo2D[];
      for (const info of infos) {
        // Reflect velocity based on collision normal
        const normal = info.normal;
        const dot = this.velocity.x * normal.x + this.velocity.y * normal.y;
        this.velocity = new APJS.Vector2f(
          this.velocity.x - 2 * dot * normal.x,
          this.velocity.y - 2 * dot * normal.y
        );
      }
    };

    const emitter = APJS.EventManager.getObjectEmitter(this.collider);
    emitter.on(APJS.CollisionEvent2D.Enter, this.collisionCallback, this);
    APJS.EventManager.getGlobalEmitter().on(APJS.EventType.RecordStart, this.onRecordStart);
  }

  onUpdate(deltaTime: number): void {
    const rb = this.getSceneObject().getComponent("RigidBody2D") as APJS.RigidBody2D;
    if (!rb) return;
    if (!this.inited) {
      this.rb = rb;
      const st = this.getSceneObject().getComponent("ScreenTransform") as APJS.ScreenTransform;
      if (st) this.startPos = new APJS.Vector2f(st.anchoredPosition.x, st.anchoredPosition.y);
      this.startGravityOn = rb.useGravity;
      this.inited = true;
    }
    const pos = rb.position;
    rb.position = new APJS.Vector2f(
      pos.x + this.velocity.x * deltaTime,
      pos.y + this.velocity.y * deltaTime
    );
  }

  onDestroy(): void {
    if (this.collisionCallback && this.collider) {
      const emitter = APJS.EventManager.getObjectEmitter(this.collider);
      emitter.off(APJS.CollisionEvent2D.Enter, this.collisionCallback, this);
    }
    APJS.EventManager.getGlobalEmitter().off(APJS.EventType.RecordStart, this.onRecordStart);
  }
}