In 4.3, 2d sprite is powerful.
But i get a problem, why the sprite is so many polygon?
can it only use 2 tris to do that?Or can i set that by myself?
Add a polygon collider to your sprite, then in the Editor, hold the Shift button down and then mouse over the polygon collider in order to see and manipulate the vertices (points) of the polygon. As you manipulate the polygon, the collider will automatically triangulate the new collider areas as a result. It will use as many triangles as necessary in order to define the new polygon shape you have defined.
I think he’s talking about the Sprite mesh, not the collider.
While you can’t edit the sprite mesh, you can force Unity to abandon it and revert to a quad instead (2 tris). The downside to this is that there could be a lot of over-draw (bad performance on mobile) depending on your sprite.
To do it, look at your Sprite import settings, change to Advanced mode, set Sprite Mode to Single and Mesh Type to Full Rect.