C++ lambda function with Qt Timer and OpenCV example.

qt_timer_within_main_with_lambda.cpp

#include <QCoreApplication>
#include <QTimer>
#include <QDebug>

#include <memory>

#include <opencv2/highgui/highgui.hpp>

int main(int argc, char** argv)
{
    QCoreApplication a(argc, argv);

    //////////////////////////////////////////////////////////////////////
    // This timer is required, because it ensures that all the code     //
    // runs in the main thread. This issue is due to, apparently,       //
    // OpenCV not showing it's windows in a thread other than the main. //
    //////////////////////////////////////////////////////////////////////
    
    std::shared_ptr<WebSocketCamera> websocketCamera(new WebSocketCamera("ws://localhost:1234/camera"));
    websocketCamera->start();
    std::shared_ptr<cv::Mat> image(new cv::Mat());

    std::shared_ptr<bool> canExit(new bool);
    *canExit = false;

    QTimer captureLoopTimer(&a);
    QObject::connect(&captureLoopTimer, &QTimer::timeout, [=]()
    {
        websocketCamera->getImage(*image);
        cv::imshow("DISPLAY", *image);
        int key = cv::waitKey(1);
        if(key != -1)
        {
            *canExit = true; 
        }
    }); 
    captureLoopTimer.start();

    QTimer monitorKeyTimer(&a);
    QObject::connect(&monitorKeyTimer, &QTimer::timeout, [=]()
    {
        if(*canExit)
        {
            QCoreApplication::quit();
        }
    });
    monitorKeyTimer.start();
    
    return a.exec();
}