handle keyevent in multi-threading application with Qt+OpenCV

rokk

I have a multi-threading application written in C++ with Qt5.7 and OpenNI. It has a main thread that starts a second thread which capture frame from a .oni recording file (asus xtion pro live) does some processing and through the Qt signal-slot mechanism pass the frame to the main thread, which display it using imshow(). What I want to do is to implement a pause key, so pressing for example 'p' the processing pause. I am thinking of something like this:

void Camera::run(){
  while(!cameraStop && this->device.isValid())
    {
      try {
        if (!buttonPause) {
            getFrame();
            process();
            emit sigFrameImageReady(frame);
            if (cv::waitKey(1)==112){
              setButtonPause(!(getButtonPause()));
           }
          }

      }
      catch(std::exception &ex) {
        std::cerr << "getFrame()" << ex.what() << std::endl;
      }
    }
}

In this way it doesn't work, I think that's because the frame is displayed by another thread (the main one), the waitKey() here simply blocks the entire process, but if I put it in the main thread, just after imshow() in this way:

void Process::FrameImageReady(cv::Mat FrameImage)
{
  if (modedebug)
    cv::imshow("bgr", FrameImage);
  if (cv::waitKey(10)==112){
    cam->setButtonPause(!(getButtonPause()));
  }
}

waitkey seems to be ignored (image displaying works fine).. any idea? Perhaps it is better to use a Qt function do it ?
It is a console application, the GUI part is only for debugging purpose.

kshegunov

Hi,
Since you've subclassed QThread and you're not using an event loop you're pretty much forced to use the low-level "solution", that is blocking with a primitive. See here for example code with a QSemaphore .