return a list waypoint indexes in view order

def view_indexes(self, done=None):
        '''return a list waypoint indexes in view order'''
        ret = []
        if done is None:
            done = set()
        idx = 0

        # find first point not done yet
        while idx < self.count():
            if not idx in done:
                break
            idx += 1
            
        while idx < self.count():
            w = self.wp(idx)
            if idx in done:
                if w.x != 0 or w.y != 0:
                    ret.append(idx)
                break
            done.add(idx)
            if w.command == mavutil.mavlink.MAV_CMD_DO_JUMP:
                idx = int(w.param1)
                w = self.wp(idx)
                if w.x != 0 or w.y != 0:
                    ret.append(idx)
                continue
            if (w.x != 0 or w.y != 0) and self.is_location_command(w.command):
                ret.append(idx)
            idx += 1
        return ret