classes.js

class Orbit {
  constructor(x, y, speed, history) {
    this.pos = createVector(x, y);
    this.vel = p5.Vector.random2D();
    this.acc = 0;
    this.speed = speed;
    this.history = [];
    this.lifespan = history || 160;
    this.vel.mult(8);
  }

  update(x, y) {
    let follow = createVector(x, y);
    this.acc = p5.Vector.sub(follow, this.pos);
    this.acc.setMag(0.8);

    this.vel.add(this.acc);
    this.vel.limit(this.speed);

    this.pos.add(this.vel);
    let v = createVector(this.pos.x, this.pos.y);
    this.history.push(v);

    if (this.history.length > this.lifespan) this.history.shift();
  }

  show() {
    beginShape();
    for (let i = 1; i < this.history.length; i++) {
      let opacity = i < 35 ? i : 35;
      stroke(100, 100, 100, opacity);
      line(
        this.history[i].x,
        this.history[i].y,
        this.history[i - 1].x,
        this.history[i - 1].y
      );
    }
    endShape();
  }
}