原地址：http://blog.csdn.net/w88193363/article/details/38331205
函数说明
| origin | The point in 2D space where the ray originates. |
| direction | Vector representing the direction of the ray. |
| distance | Maximum distance over which to cast the ray. |
| layerMask | Filter to detect Colliders only on certain layers. |
| minDepth | Only include objects with a Z coordinate (depth) greater than this value. |
| maxDepth | Only include objects with a Z coordinate (depth) less than this value. |
Casts a ray against colliders in the scene, returning all colliders that contact with it.发射一条射线到场景中，检测射线射到的所有碰撞机(collider）
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原文：http://www.cnblogs.com/123ing/p/3911959.html
