CollisionEvent2D

2D collision event types.

Type	Name	Interface Description
Variables	Enter: UserEventType	• Function: Fired once when the 2D physics engine reports that this collider has just started colliding.
Variables	Exit: UserEventType	• Function: Fired once when the 2D physics engine reports that a previous collision has ended.
Variables	Stay: UserEventType	• Function: Fired on each physics step while the 2D physics engine reports that the collision is still active.
Functions	constructor()

Examples

constructor()

let obj = new APJS.CollisionEvent2D();

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 — Tap to drop a ball/coin that bounces multiple times on a static floor — full Physics Matter resource flow (DSL: add_builtin_resource → set_resource_properties →…

@component()
export class TapToDropBouncy extends APJS.BasicScriptComponent {
  private rb: APJS.RigidBody2D | null = null;
  private collider: APJS.CircleCollider2D | null = null;
  private touchCallback: ((event: APJS.IEvent) => void) | null = null;
  private collisionCallback: ((event: APJS.IEvent) => void) | null = null;
  private dropped = false;
  private bounceCount = 0;

  onStart(): void {
    const obj = this.getSceneObject();
    this.rb = obj.getComponent("RigidBody2D") as APJS.RigidBody2D;
    this.collider = obj.getComponent("CircleCollider2D") as APJS.CircleCollider2D;
    if (!this.rb || !this.collider) return;

    // emitCollisionEvent is APJS-runtime-only — must set in onStart, not in DSL.
    this.collider.emitCollisionEvent = true;

    this.touchCallback = (event: APJS.IEvent) => {
      const touch = event.args[0] as APJS.TouchData;
      if (touch.phase === APJS.TouchPhase.Began && !this.dropped && this.rb) {
        this.dropped = true;
        this.rb.static = false;  // gravity now applies
      }
    };
    APJS.EventManager.getGlobalEmitter().on(APJS.EventType.Touch, this.touchCallback);

    this.collisionCallback = (event: APJS.IEvent) => {
      this.bounceCount++;
      // Optional: stop tracking after 5 bounces, or play SFX, or update score, etc.
      if (this.bounceCount === 1) console.log("[Bouncy] first impact");
    };
    const emitter = APJS.EventManager.getObjectEmitter(this.collider);
    emitter.on(APJS.CollisionEvent2D.Enter, this.collisionCallback, this);
  }

  onDestroy(): void {
    if (this.touchCallback) {
      APJS.EventManager.getGlobalEmitter().off(APJS.EventType.Touch, this.touchCallback);
    }
    if (this.collisionCallback && this.collider) {
      APJS.EventManager.getObjectEmitter(this.collider).off(APJS.CollisionEvent2D.Enter, this.collisionCallback, this);
    }
  }
}