官方自带的寻路改编为2D，很好用

unity2D寻路Navigation2D (Pathfinding for 2D Games)  V1.27
要求Unity 2017.4.1 或更高版本。

Navigation2D uses Unity's built-in Navigation system to make 2D pathfinding possible without any axis rotations.
Usage:
1. Make 2D Colliders static
2. Go to Navigation2D, select Bake
3. Use NavMeshAgent2D to move

Components:
* Uses built in BoxCollider2D
* Uses built in CircleCollider2D
* Uses built in EdgeCollider2D
* Uses built in PolygonCollider2D
* Uses built in TilemapCollider2D
* Wraps NavMeshAgent for 2D
* Wraps NavMeshObstacle for 2D