proton-engine/src/behaviour/Collision.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 Collision extends Behaviour {
  /**
   * The callback after collision
   *
   * @callback Callback
   *
   * @param {Proton.Particle} particle
   * @param {Proton.Paritcle} otherParticle
   */
  /**
   * @memberof! Proton#
   * @augments Proton.Behaviour
   * @constructor
   * @alias Proton.Collision
   *
   * @todo add description to mass
   *
   * @param {Proton.Emitter} 	[emitter=null] 		the attraction point coordinates
   * @param {Boolean} 		[mass=true]
   * @param {Callback}	 	[callback=null]		the callback after the collision
   * @param {Number} [life=Infinity] 				this behaviour's life
   * @param {String} [easing=ease.easeLinear] 	this behaviour's easing
   *
   * @property {String} name The Behaviour name
   */
  constructor(emitter, mass, callback, life, easing) {
    super(life, easing);
    this.reset(emitter, mass, callback);
    this.newPool = [];
    this.pool = [];
    this.name = "Collision";
  }

  /**
   * Reset this behaviour's parameters
   *
   * @memberof Proton#Proton.Collision
   * @method reset
   * @instance
   *
   * @todo add description to mass
   *
   * @param {Proton.Emitter} 	[emitter=null] 		the attraction point coordinates
   * @param {Boolean} 		[mass=true]
   * @param {Callback}	 	[callback=null]		the callback after the collision
   * @param {Number} 			[life=Infinity] 	this behaviour's life
   * @param {String} [easing=ease.easeLinear] 	this behaviour's easing
   */
  reset(emitter, mass, callback, life, easing) {
    this.emitter = Util.initValue(emitter, null);
    this.mass = Util.initValue(mass, true);
    this.callback = Util.initValue(callback, null);

    this.collisionPool = [];
    this.delta = new Vector2D();

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

  /**
   * Apply this behaviour for all particles every time
   *
   * @memberof Proton#Proton.Collision
   * @method applyBehaviour
   * @instance
   *
   * @param {Proton.Particle} particle
   * @param {Number} 			time the integrate time 1/ms
   * @param {Int} 			index the particle index
   */
  applyBehaviour(particle, time, index) {
    if (this.emitter) {
      Util.sliceArray(this.emitter.particles, index, this.newPool);
    } else {
      Util.sliceArray(this.pool, index, this.newPool);
    }

    const length = this.newPool.length;
    let otherParticle;
    let lengthSq;
    let overlap;
    let totalMass;
    let averageMass1, averageMass2;
    let i;

    for (i = 0; i < length; i++) {
      otherParticle = this.newPool[i];

      if (otherParticle !== particle) {
        this.delta.copy(otherParticle.p);
        this.delta.sub(particle.p);

        lengthSq = this.delta.lengthSq();
        const distance = particle.radius + otherParticle.radius;

        if (lengthSq <= distance * distance) {
          overlap = distance - Math.sqrt(lengthSq);
          overlap += 0.5;

          totalMass = particle.mass + otherParticle.mass;
          averageMass1 = this.mass ? otherParticle.mass / totalMass : 0.5;
          averageMass2 = this.mass ? particle.mass / totalMass : 0.5;

          particle.p.add(
            this.delta
              .clone()
              .normalize()
              .multiplyScalar(overlap * -averageMass1)
          );
          otherParticle.p.add(this.delta.normalize().multiplyScalar(overlap * averageMass2));

          this.callback && this.callback(particle, otherParticle);
        }
      }
    }
  }
}