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