DistanceJoint2D

A 2D distance joint.

Type	Name	Interface Description
Functions	constructor()

Examples

constructor()

let obj = new APJS.DistanceJoint2D();

Use Case

Rigid 2D pendulum using DistanceJoint2D — anchor (static RigidBody2D) + bob (dynamic RigidBody2D, useGravity=true) connected by a DistanceJoint2D on the bob.

// Optional helper — the pendulum SWINGS WITHOUT THIS SCRIPT (joint + gravity is enough).
// Attach this to the bob if you need to react to each swing pass (count swings, play tick SFX,
// trigger an animation when the bob crosses the bottom). Reads ScreenTransform.localPosition;
// detects sign-flips of the lateral offset relative to the anchor's known X.
@component()
export class PendulumSwingCounter extends APJS.BasicScriptComponent {
  @serializeProperty
  anchorX: number = 0;  // anchor's world-X in localPosition coords (computed at scene-build time)

  private st: APJS.ScreenTransform | null = null;
  private lastSign: number = 0;
  private swings: number = 0;

  onStart(): void {
    this.st = this.getSceneObject().getComponent("ScreenTransform") as APJS.ScreenTransform;
  }

  onUpdate(dt: number): void {
    if (!this.st) return;
    const dx = this.st.localPosition.x - this.anchorX;
    const sign = dx === 0 ? 0 : (dx > 0 ? 1 : -1);
    if (sign !== 0 && this.lastSign !== 0 && sign !== this.lastSign) {
      this.swings++;
      // Hook: play SFX, advance game state, etc.
      console.log("[Pendulum] swing #" + this.swings);
    }
    if (sign !== 0) this.lastSign = sign;
  }
}