Perspectively transform points

After we get the transformation matrix 'trans_mat' from the 'getPerspectiveTransform', we can transform a point in this way

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        cv::Point2f src = cv::Point2f(123, 456);
        std::vector<cv::Point2f> in_pts, out_pts;
        in_pts.push_back(src);
        cv::perspectiveTransform(in_pts, out_pts, trans_mat);
        cv::Point2f dst = out_pts.front();

refer to:
https://blog.csdn.net/xiaowei_cqu/article/details/26478135