proton-engine/src/behaviour/GravityWell.js

Proton is a simple and powerful javascript particle animation engine.

import Util from "../utils/Util";
import Vector2D from "../math/Vector2D";
import Behaviour from "./Behaviour";

export default class GravityWell extends Behaviour {
  /**
   * @memberof! Proton#
   * @augments Behaviour
   * @constructor
   * @alias GravityWell
   *
   * @param {Vector2D} [centerPoint=new Vector2D] The point in the center
   * @param {Number} [force=100]					The force
   * @param {Number} [life=Infinity]				this behaviour's life
   * @param {String} [easing=easeLinear]	this behaviour's easing
   *
   * @property {String} name The Behaviour name
   */
  constructor(centerPoint, force, life, easing) {
    super(life, easing);

    this.distanceVec = new Vector2D();
    this.centerPoint = Util.initValue(centerPoint, new Vector2D());
    this.force = Util.initValue(this.normalizeValue(force), 100);

    this.name = "GravityWell";
  }

  /**
   * Reset this behaviour's parameters
   *
   * @method reset
   * @memberof Proton#GravityWell
   * @instance
   *
   * @param {Vector2D} [centerPoint=new Vector2D] The point in the center
   * @param {Number} [force=100]					The force
   * @param {Number} [life=Infinity]				this behaviour's life
   * @param {String} [easing=easeLinear]	this behaviour's easing
   */
  reset(centerPoint, force, life, easing) {
    this.distanceVec = new Vector2D();
    this.centerPoint = Util.initValue(centerPoint, new Vector2D());
    this.force = Util.initValue(this.normalizeValue(force), 100);

    life && super.reset(life, easing);
  }

  /**
   * @inheritdoc
   */
  initialize(particle) {}

  /**
   * Apply this behaviour for all particles every time
   *
   * @method applyBehaviour
   * @memberof Proton#GravityWell
   * @instance
   *
   * @param {Particle} particle
   * @param {Number} the integrate time 1/ms
   * @param {Int} the particle index
   */
  applyBehaviour(particle, time, index) {
    this.distanceVec.set(this.centerPoint.x - particle.p.x, this.centerPoint.y - particle.p.y);
    const distanceSq = this.distanceVec.lengthSq();

    if (distanceSq !== 0) {
      const distance = this.distanceVec.length();
      const factor = (this.force * time) / (distanceSq * distance);

      particle.v.x += factor * this.distanceVec.x;
      particle.v.y += factor * this.distanceVec.y;
    }
  }
}