grid_unwrap_position
grid_unwrap_position(s->grid, cx, cy, wx, wy);
void grid_unwrap_position(struct grid *, u_int *, u_int *, u_int, u_int);
grid_unwrap_position(gd, &cx, &cy, wx, wy);
grid_unwrap_position(dst->grid, cx, cy, wx, wy);