   Particle.prototype.update = function(deltaTime) {
      this.position.x += this.velocity.x * deltaTime;
      this.position.y += this.velocity.y * deltaTime;
      this.velocity.x += this.acceleration.x * deltaTime;
      this.velocity.y += this.acceleration.y * deltaTime;
      this.age += deltaTime;
    };

    Particle.prototype.draw = function(context, image) {
      function ease(t) {
        return (--t) * t * t + 1;
      }
      var size = image.width * ease(this.age / settings.partic