opencv图像重映射

cv::remap  (   
    InputArray    src,
    OutputArray    dst,
    InputArray    map1,
    InputArray    map2,
    int        interpolation,
    int        borderMode = BORDER_CONSTANT,
    const Scalar    borderValue = Scalar()
    )

#include"pch.h"
#include<iostream>
#include<opencv2\opencv.hpp>

using namespace std;
using namespace cv;

#define INPUT_TITLE "input image"
#define OUTPUT_TITLE "remap image"

Mat img, src;//img 输入图像 ; src 最终输出的图像
Mat map_x, map_y;
int index = 0;
void updata_map();

int main() {

    img = imread("b.jpg");
    if (!img.data)
    {
        cout << "ERROR : could not load image.";
        return -1;
    }
    namedWindow(INPUT_TITLE, CV_WINDOW_AUTOSIZE);
    namedWindow(OUTPUT_TITLE, CV_WINDOW_AUTOSIZE);

    imshow(INPUT_TITLE, img);

    //建立映射表
    map_x.create(img.size(), CV_32FC1);
    map_y.create(img.size(), CV_32FC1);

    int c = 0;
    while (true)
    {
        c = waitKey(500);
        index = c % 4;
        if ((char)c == 27)
        {
            break;
        }
        updata_map();
        remap(img, src, map_x, map_y, INTER_LINEAR, BORDER_CONSTANT, Scalar(0, 0, 255));
        imshow(OUTPUT_TITLE, src);
    }


    return 0;
}

void updata_map() {
    for (int row = 0; row < img.rows; row++)
    {
        for (int col = 0; col < img.cols; col++)
        {
            switch (index)
            {
                //index = 0 ，图像的行跟列为为原来的1/2。
                //index = 1，为左右翻转（列变换，行不变）
                //index = 2，为上下翻转（行变换，列不变）
                //index = 3，为中心旋转

            case 0:
                if (col > (img.cols*0.25) && col<(img.cols*0.75) && row>(img.rows*0.25) && row < (img.rows*0.75)) {
                    map_x.at<float>(row, col) = 2 * (col - (img.cols*0.25));
                    map_y.at<float>(row, col) = 2 * (row - (img.rows*0.25) - 0.25);
                }
                else
                {
                    map_x.at<float>(row, col) = 0;
                    map_y.at<float>(row, col) = 0;
                }
                break;
            case 1:
                map_x.at<float>(row, col) = (img.cols - col - 1);
                map_y.at<float>(row, col) = row;
                break;
            case 2:
                map_x.at<float>(row, col) = col;
                map_y.at<float>(row, col) = (img.rows - row - 1);
                break;
            case 3:
                map_x.at<float>(row, col) = (img.cols - col - 1);
                map_y.at<float>(row, col) = (img.rows - row - 1);
                break;

            default:
                break;
            }
        }
    }
}