subVectors(a, b) {
    this.x = a.x - b.x;
    this.y = a.y - b.y;

    return this;
  }
Subtracts one vector from another and sets the result to this vector.
@param {Vector2D} a - The vector to subtract from.
@param {Vector2D} b - The vector to subtract.
@returns {Vector2D} This vector.