6. [opencv mouse callback event]

(一)、What is a mouse callback event and what it does？

简单的理解:The mouse callback time is when we are in the compile window,Our mouse works
And will return the two-dimensional coordinates of our mouse movement.

（二）、We need to know thoseAPI？

1.回调函数:

Functions declared outside the class、其基本格式为:

void mouse_callback(int event, int x, int y, int flag, void* userdata)         //回调函数
{
    
	cout << event << " " << x << " " << y << " " << flag << " "<< endl;          //打印函数.
}

The constructor parameter format is :
event：（This article follows the basics.That is, numbers)鼠标事件
0=滑动;
1=左键点击;2=右键点击;3=China Construction Click;
4=左键放开;5=右键放开;6=右键放开;
7=左键双击;8=右键双击;9=Zhongjian double click;
x和y:鼠标指针在图像坐标系的坐标

flagsMouse key combinations are displayed:

usderata: 用户自定义参数:

2.设置鼠标回调函数:

Its name is a fixed name:SetMouseCallback(窗口名字,Callback function name,usdedata)
主要目的：is the response window.

setMouseCallback("鼠标事件", mouse_callback);          //设置鼠标回调函数

(三)Operational thinking and basic thinking:

First we have to set back to the functionmousecallback;Then perform various operations of the window to print out the mouse.Then read in the image in the main function,设置窗口,Set the mouse callback function,显示帧数、Finally destroy the window.

(四)、实战项目:

1.代码展示:

#include <iostream>
#include <opencv2/opencv.hpp>
using namespace std;
using namespace cv;
void mouse_callback(int event, int x, int y, int flag, void* userdata)         //回调函数
{
    
	cout << event << " " << x << " " << y << " " << flag << " "<< endl;          //打印函数.
}

int main()
{
    
	Mat imag;
	imag = imread("xx.jpg");                                //读入图像
	namedWindow("鼠标事件",WINDOW_NORMAL);
	setMouseCallback("鼠标事件", mouse_callback);          //设置鼠标回调函数
	while (1)
	{
    
		imshow("鼠标事件", imag);                         //展示窗口
		if (waitKey(25) == 27)break;                      //Display frame rate
	}
	cout << "程序退出:" << endl;
	destroyAllWindows();
	return 0;
}

2.效果展示: