CODEWITHSUNDEEP
c++opencv
Selie
Selie

Reputation: 43

opencv window not refreshing at mouse callback

I am trying to draw with mouse move in an opencv window. But when I draw, nothing draws on the window. When I try to close the window from the cross in the topleft(ubuntu), it opens a new window which it should be as I haven't pressed escape, and in this new window, I am able to see my drawing. I can't understand the problem. I think something is wrong with window refreshing with mouse call back. Here is the code...

bool drawing = false; //true if mouse is pressed
Mat img;

void draw(int event, int x, int y, int flags, void* param){
     if (event == CV_EVENT_LBUTTONDOWN){
        drawing = true;
    } else if (event == CV_EVENT_MOUSEMOVE){
        if (drawing) circle(img,Point(x,y),4,Scalar(255,255,255),-1);
    } else if (event == CV_EVENT_LBUTTONUP){
        drawing = false;
        circle(img,Point(x,y),2,Scalar(255,255,255),-1);
    }
}

int main(){
    // Create black empty images
    img = Mat::zeros(window_width, window_height, CV_8UC3);

    namedWindow( window_name, CV_WINDOW_AUTOSIZE );     // Create a window for display.
    setMouseCallback(window_name, draw, &img);          //set the callback function for any mouse event

    while(true){
        imshow(window_name, img);
        if (waitKey(0) == 27) break;
    }

    destroyAllWindows();
    return 0;
}

Any help,please?

Upvotes: 1

Views: 1424

Answers (1)

Micka
Micka

Reputation: 20130

your code works for me.

But you used cv::waitKey(0) which means that the program waits there until you press a keyboard key. So try pressing a key after drawing, or use cv::waitKey(30) instead.

If this doesnt help you, please add some std::cout in your callback function to verify it is really called.

btw, Mat::zeros(window_width, window_height, CV_8UC3); probably should be Mat::zeros(window_height, window_width, CV_8UC3); instead if you variable names shall be intuitive

Upvotes: 2

Related Questions