warp_demo_in_one_window.cpp

//
//  main.cpp
//  warp_in_one_window
//
//  Created by GoldenGrape on 2020/6/8.
//  Copyright © 2020 goldengrape. All rights reserved.
//

#include "opencv2/imgproc.hpp"
#include "opencv2/imgcodecs.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/calib3d.hpp"
#include <iostream>
using namespace std;
using namespace cv;

vector<Point2f> d_corner(4);
vector<Point2f> o_corner(4);

float width, height;
bool dragging=false;

int selected_corner_i=-1;
Mat H, H_inv;
void init_corners(vector<Point2f> &corner, float width, float height);
void point_warp(Point2f &p_target, const Point2f &p, const Mat &H);
void onMouse(int event, int x, int y, int, void*);


int main(int argc, const char * argv[]) {
//    读取图像
    String filename="/Volumes/macTF/lena.png";
    Mat img=imread(filename);
    width=img.cols; height=img.rows;
//    初始设置参考点为四角
    init_corners(d_corner,width,height);
    init_corners(o_corner, width, height);
//    初始化映射矩阵, 实际上是单位矩阵
    H = findHomography(o_corner, d_corner);
    H_inv=H;
//    设置鼠标控制
    String win_name="Only one window";
    namedWindow(win_name);
    setMouseCallback(win_name, onMouse, 0);
//    显示变换图像
    bool endProgram = false;
    while(!endProgram){
//        控制按键
        char c = (char)waitKey( 10 );
//        按q、Q、esc退出
        if ((c == 'q') | (c == 'Q') | (c == 27))
        {
            endProgram = true;
        }
//        按r、R旋转
        if ((c == 'r') | (c == 'R'))
        {
            o_corner.push_back(o_corner[0]);
            o_corner.erase(o_corner.begin());
        }
        
//        计算映射矩阵H和逆矩阵H_inv
        H = findHomography(o_corner, d_corner); //get homography
        H_inv= findHomography(d_corner, o_corner);
//        将原始图像映射到新位置上
        Mat warped_image;
        warpPerspective(img, warped_image, H, Size(width,height));
        imshow(win_name, warped_image);
    }

    return 0;
}

void init_corners(vector<Point2f> &corner, float width, float height){
//    初始化时, 将四角作为参考点
    corner[0]=Point2f(0,0);
    corner[1]=Point2f(width,0);
    corner[2]=Point2f(width,height);
    corner[3]=Point2f(0,height);
}

void onMouse(int event, int x, int y, int, void*){
//    有点复杂
//    当鼠标按下时在变形图上找到一点(x,y), 然后找到这一点在原始图上的位置o_corner
//    当鼠标拖动时, 相当于要将原始图上o_corner映射到鼠标点位置
    if(event == EVENT_LBUTTONDOWN){
//        以四个象限来规定鼠标点的所属
        if (x<width/2){
            selected_corner_i=(y < height/2)?0:3;
        } else if (x>=width/2){
            selected_corner_i=(y < height/2)?1:2;
        }
        dragging= true;
        d_corner[selected_corner_i]=Point2f((float)x,(float)y);
//        通过映射矩阵的逆矩阵H_inv, 计算当前(x,y)点在原始图的位置
        point_warp(o_corner[selected_corner_i],
                   d_corner[selected_corner_i],
                   H_inv);
    } else if (event==EVENT_LBUTTONUP) {
        dragging= false;
    }
    if (dragging & (event == EVENT_MOUSEMOVE) ){
        d_corner[selected_corner_i]=Point2f((float)x,(float)y);
    }
}

void point_warp(Point2f &p_target, const Point2f &p, const Mat &H){
//    映射矩阵H是一个3x3的矩阵,
//    s*[p_target.x, p_target.y, 1]= H * [p.x, p.y, 1]
//    乘出来以后要对第三项归一化
    Mat p_vector = (Mat_ <double>(3, 1) << p.x,p.y, 1);
    p_vector = H * p_vector;
    p_target.x=(float)(p_vector.at<double>(0)/p_vector.at<double>(2));
    p_target.y=(float)(p_vector.at<double>(1)/p_vector.at<double>(2));
}