sub(v, w) {
    if (w !== undefined) {
      return this.subVectors(v, w);
    }

    this.x -= v.x;
    this.y -= v.y;

    return this;
  }
Subtracts another vector from this one.
@param {Vector2D} v - The vector to subtract.
@param {Vector2D} [w] - An optional second vector to subtract.
@returns {Vector2D} This vector.