cvWaitKey(x) / cv::waitKey(x)
does two things:
- It waits for x milliseconds for a key press on a OpenCV window (i.e. created from
cv::imshow()
). Note that it does not listen on stdin for console input. If a key was pressed during that time, it returns the key’s ASCII code. Otherwise, it returns-1
. (Ifx <= 0
, it waits indefinitely for the key press.) - It handles any windowing events, such as creating windows with
cv::namedWindow()
, or showing images withcv::imshow()
.
A common mistake for opencv newcomers is to call cv::imshow()
in a loop through video frames, without following up each draw with cv::waitKey(30)
. In this case, nothing appears on screen, because highgui is never given time to process the draw requests from cv::imshow()
.