Trying to close OpenCV window has no effect

Question

I'm capturing the webcam image with OpenCV. That works fine. But if I want to close the OpenCV when a button is pressed, it does not work (tried both cvDestroyWindow("NameOfWindow")and cvDestroyAllWindows()). The window stays open and the application is still running.

The OpenCV was initialized on separate thread from the main GUI.

I'm using the Juce Framework with C++ on my Mac. But the same problem occurs also on Windows with Qt and Windows Forms, when the OpenCV Window has it's own cvNamedWindow.

Here is the basic code of the VST plugin editor class:

PluginEditor.cpp

#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>

#include "PluginProcessor.h"
#include "PluginEditor.h"

//
TestAudioProcessorEditor::TestAudioProcessorEditor (TestAudioProcessor* ownerFilter)
: AudioProcessorEditor (ownerFilter)
{   

    // This is where our plugin's editor size is set.
    setSize (500, 500);

    // open the tracker
    openTracker();
}   

// code for opencv handling
TestAudioProcessorEditor::openTracker() {

    // KEY LINE: Start the window thread
    cvStartWindowThread();

    // Create a window in which the captured images will be presented
    cvNamedWindow( "Webcam", CV_WINDOW_AUTOSIZE );  

    cvWaitKey(0);

    cvDestroyWindow( "Webcam" );
    // window should disappear!
}


TestAudioProcessorEditor::~TestAudioProcessorEditor()
{

}

// paint stuff on the vst plugin surface
void TestAudioProcessorEditor::paint (Graphics& g) {   
}   

Answer 1

The piece you may be missing is a call to the cvStartWindowThread function.

On Linux, using the GTK HighGUI, this example reproduced your problem, until I put in the call to cvStartWindowThread.

#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc_c.h"

#include <iostream>
using namespace std;

int main( int argc, char** argv )
{
    // KEY LINE: Start the window thread
    cvStartWindowThread();

    // Open a window
    cvNamedWindow("original", 0);

    // Wait until a key gets pressed inside the window
    cvWaitKey(0);

    // Close the window
    cvDestroyWindow("original");

    // Verify that the window is closed
    cout<<"The window should be closed now. (Press ENTER to continue.)"<<endl;
    string line;
    getline(cin, line);
    cout<<"Exiting..."<<endl;
}

If cvStartWindowThread doesn't help, try doing an extra call to cvWaitKey after your cvDestroy call.

To run the example, compile it with GCC:

g++ destroy_window.cpp -o destroy_window -lopencv_core -lopencv_highgui