OpenCV OpenGLDrawCallback doesn't get called - c++

Question

I initialize OpenCV window with following code:
cv::VideoCapture * stream = new cv::VideoCapture("stream_ip");
if (!stream->isOpened()){
printf("Couldn't open stream! %s\n", strerror(errno));
}
//We create window with OpenGL enabled.
cv::namedWindow("rtsp_stream", cv::WINDOW_OPENGL);
//Make it fullscreen (I also tried with fixed screen size without luck.)
cv::setWindowProperty("rtsp_stream", cv::WND_PROP_FULLSCREEN, cv::WINDOW_FULLSCREEN);
//Set OpenGL context to use this window.
cv::setOpenGlContext("rtsp_stream");
//Set openGlDrawCallback.
cv::setOpenGlDrawCallback("rtsp_stream", on_opengl, NULL);
//This is the material that the image will be rendered on.
cv::Mat frame;
char k;
bool continueStream = true;
while (continueStream) {
//We read data from the stream and write it on the frame.
if((stream->read(frame)) != 0){
//Then we display/render the image using imshow.
cv::imshow("rtsp_stream", frame);
k = cv::waitKey(1);
//I'm not sure if updateWindow needs to be manually called to make openGLDrawCallback or if imshow calls it automatically after done rendering. So I have tried with and without it.
//cv::updateWindow("rtsp_stream");
switch(k){
case 0x1b: //ESC key
printf("Closing stream.\n");
continueStream = false;
break;
}
}
}
open_gl function just simply fprints some text to see if opengldrawcallback gets called. I have also made sure I have OpenGL and QT enabled on my OpenCV with std::cout << cv::getBuildInformation() << std::endl;. I have tried to find solutions from many different websites and sources, including this book. Program works as expected in every manner, except that openglcallback never gets called. All the help is much appreciated.

Answer 1

Okay. so as I yesterday found out, cv::imshow prevented me from using OpenGL commands on that window.
So what I had to do to overcome this, was to read the data on a cv::Mat, just like before. But instead of rendering that cv::Mat straight on the window using cv::imshow, I had to first store the data on a texture and then render that texture on screen. To store the data on a texture I used the following method:
/**
*texture: Pointer to OpenGL texture that we want to render our stream on.
*data: cv::Mat that contains the data we want to render.
**/
void storeStreamToTexture(GLuint texture, cv::Mat* data){
//Bind the texture we want to render to.
glBindTexture(GL_TEXTURE_2D, texture);
//we flip the Mat to start reading from the beginning.
cv::flip(*data, *data, 0);
//Store mat data to our texture.
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, data->cols, data->rows, 0, GL_BGR, GL_UNSIGNED_BYTE, data->data);
}
And after that we can use our texture like we would use any other texture on OpenGL. Hope someone finds this useful in the future! :)