cv::setMouseCallBack does not work on MacOS

MacOSX

asked 2017-06-26 12:32:54 -0600

Dear All,

I have started to learn OpenCV. But have a question.

My MacOS version is Sierra 10.12.5. I downloaded opencv and opencv_contrib repos and build using CMAKE 3.8.2, everything seems ok.But I wrote this sample (see Github) to test my installation every line of code works well but mouseCallBack doesn't work as expected.

I would be pleased if anyone give me another perspective.

Regards. Mehmet.

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answered 2017-06-26 23:47:13 -0600

berak
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apple users always suspect, that it's about their funny little boxes, but here - not so.

your mouse handler expects to be passed an image via the void* param, but you fail to give it an image

so, that should be:

cv::setMouseCallback(ORIGINAL_WINDOW_NAME, MouseHandler::onMouse, (void*)(&image));

you also should check for invalid pointers:

void  MouseHandler::onMouse(int event, int x, int y, int, void *param) {
    std::cout << "Mouse event fired!" << std::endl;
    if (!param) {
        std::cout << "there is no image !!" << std::endl;
        return;
    }
    cv::Mat *im = static_cast<cv::Mat *>(param);
    ....