code: function Mat22(a, b, c, d) {
    if (typeof a === 'object' && a !== null) {
      this.ex = Vec2.clone(a);
      this.ey = Vec2.clone(b);
    } else if (typeof a === 'number') {
      this.ex = Vec2.neo(a, c);
      this.ey = Vec2.neo(b, d)
    } else {
      this.ex = Vec2.zero();
      this.ey = Vec2.zero()
    }
  }
docs: A 2-by-2 matrix. Stored in column-major order.