Main camera processing loop for a desktop app

If you want to display a GUI window on the screen using OpenCV, you call cv::imshow() 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 indefinitely 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 main_desktop.cpp, as the basis for 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 at least 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.
  char keypress = cv::waitKey(20);  // Need this to see anything!
  if (keypress == 27) {   // Escape Key
  // Quit the program!
  break;
  }
}//end while