OpenCV鼠标响应函数（setMouseCallback）

此处给出OpenCV中的鼠标回调函数，实现功能：将鼠标左键点击处的图像像素值显示在终端。

/*
    void setMousecallback(const string& winname, MouseCallback onMouse, void* userdata=0)
    winname：窗口名
    onMouse:鼠标响应函数，原型：void on_Mouse(int event, int x, int y, int flags, void* param);
    userdata:可认为是传给回调函数的参数
*/
#include <iostream>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>

using namespace std;
using namespace cv;
const char* windows_name = "onMouseCallback";

void on_Mouse(int event, int x, int y, int flags, void* param);

int main(int argc, char* argv[])
{
    Mat src = imread("imgA.png",-1);
    if (src.empty())
    {
        cout << "The image is empty, please check it!" << endl;
        return -1;
    }
    namedWindow(windows_name);
    setMouseCallback(windows_name, on_Mouse,(void*)&src); //类型转换
    imshow(windows_name, src);
    
    waitKey();
    return 0;
}
void on_Mouse(int event, int x, int y, int flags, void* param) {
    Mat depth_img = *(Mat*)param; // 先转换类型，再取数据
    Vec3b depth;    // 初始化不可放在case内

    // 一般包含如下3个事件
    switch (event)
    {
    case EVENT_MOUSEMOVE:
        //cout << "Please select one point:" << endl;
        break;
    case EVENT_LBUTTONDOWN: // 鼠标左键按下
        depth = depth_img.at<Vec3b>(x, y);
        cout << "Position: (" << x << "," << y
            << ")—— depth = " << depth << endl;
        break;
    case EVENT_LBUTTONUP: // 鼠标左键释放
        cout << "buttonup" << endl;
        break;
    }
}