handleAt
The handle at position for a crop currently at rect.
A corner wins over an edge when both sit within touchRadiusPx. A position inside rect but away from every edge answers CropHandle.Body, and a position outside both the rectangle and its handles answers null.
Return
The handle under position, or null.
Parameters
position
Where the pointer is, in the overlay's own coordinate space.
rect
The crop rectangle the handles are drawn around.
touchRadiusPx
How far from a handle a position still counts as touching it.