Explanation

• Create a window.

• Start event loop. This event loop will run until user terminates it by pressing e, E, q, Q.

• Access same window via its name. Since windows are implicitly shared, sameWindow is exactly the same withmyWindow. If the name does not exist, a new window is created.
• Start a controlled event loop. Once it starts, wasStopped is set to false. Inside the while loop, in each iteration, spinOnce is called to prevent event loop from completely stopping. Inside the while loop, user can execute other statements including those which interact with the window.

Code

#include <opencv2/viz/vizcore.hpp>#include <iostream>using namespace cv;using namespace std;/*** @function main*/int main(){    /// Create a window    viz::Viz3d myWindow("Viz Demo");    /// Start event loop    myWindow.spin();    /// Event loop is over when pressed q, Q, e, E    cout << "First event loop is over" << endl;    /// Access window via its name    viz::Viz3d sameWindow = viz::getWindowByName("Viz Demo");    /// Start event loop    sameWindow.spin();    /// Event loop is over when pressed q, Q, e, E    cout << "Second event loop is over" << endl;    /// Event loop is over when pressed q, Q, e, E    /// Start event loop once for 1 millisecond    sameWindow.spinOnce(1, true);    while(!sameWindow.wasStopped())    {        /// Interact with window        /// Event loop for 1 millisecond        sameWindow.spinOnce(1, true);    }    /// Once more event loop is stopped    cout << "Last event loop is over" << endl;    return 0;}

OpenCV Tutorials —— Launching Viz