drag_result_t drag_pointer(Con *con, const xcb_button_press_event_t *event, xcb_window_t confine_to, int cursor, bool use_threshold, callback_t callback, const void *extra)
This function grabs your pointer and keyboard and lets you drag stuff around (borders).
void(* callback_t)(Con *, Rect *, uint32_t, uint32_t, const xcb_button_press_event_t *, const void *)
Callback for dragging.