在 2D 物理中，有关射线投射检测到的对象的返回信息。
A raycast is used to detect objects that lie along the path of a ray and is conceptually like firing a laser beam into the Scene and observing which objects are hit by it. The RaycastHit2D class is used by Physics2D.Raycast and other functions to return information about the objects detected by raycasts.
另请参阅：Physics2D.Raycast、Ray2D 类。