In such a world there are **infinite** number of paths from S to T. Let's denote the coordinates of T by `(Tx, Ty)`, the coordinates of S by `(Sx, Sy)`, and the size of the world by `(Wx, Wy)`. The wrapped coordinates of T are `(Tx + j * Wx, Ty + i * Wy)`, where `i` and `j` are integers, that is, elements of the set `{..., -2, -1, 0, 1, 2, ...}`. The vectors connecting S to T are `(Dx, Dy) := (Tx + j * Wx - Sx, Ty + i * Wy - Sy)`. For a given `(i, j)` pair, the distance is the length of the vector, `sqrt(Dx * Dx + Dy * Dy)`, and the direction in radians is `atan(Dy / Dx)`. The **shortest path** is one of the 9 paths, where `i` and `j` are in `{-1, 0, 1}`:
![enter image description here][1]

I would calculate all of these 9 distances, and find the shortest path using simple **linear search**. (Calculating only the square of distances is enough, so there is no need to take the square root.)


  [1]: https://i.sstatic.net/dzbu3.png