Main camera processing loop for a desktop app

If you want to display a GUI window on the screen using OpenCV, you call the cv::namedWindow() function and then the cv::imshow() function for each image, but you must also call cv::waitKey() once per frame, otherwise your windows will not update at all! Calling cv::waitKey(0) waits forever until the user hits a key in the window, but a positive number such as waitKey(20) or higher will wait for at least that many milliseconds.

Put this main loop in the main.cpp file, as the basis of your real-time camera app:

while (true) { 
    // Grab the next camera frame. 
    cv::Mat cameraFrame; 
    camera >> cameraFrame; 
    if (cameraFrame.empty()) { 
        std::cerr<<"ERROR: Couldn't grab a camera frame."<< 
        std::endl; 
        exit(1); 
    } 
    // Create a blank output image, that we will draw onto. 
    cv::Mat displayedFrame(cameraFrame.size(), cv::CV_8UC3); 

    // Run the cartoonifier filter on the camera frame. 
    cartoonifyImage(cameraFrame, displayedFrame); 

    // Display the processed image onto the screen. 
    imshow("Cartoonifier", displayedFrame); 

    // IMPORTANT: Wait for atleast 20 milliseconds, 
    // so that the image can be displayed on the screen! 
    // Also checks if a key was pressed in the GUI window. 
    // Note that it should be a "char" to support Linux. 
    auto keypress = cv::waitKey(20); // Needed to see anything! 
    if (keypress == 27) { // Escape Key 
       // Quit the program! 
       break; 
    } 
 }//end while