c++ - 如何在类里面使用 cv::setMouseCallback？

Question

我想在设置类中使用 cv::setMouseCallback 来选择图片区域。这是我的代码:

void Settings::on_buttonXML_clicked(){
    cv::VideoCapture webcam;
    webcam.open(INDEX);    
    webcam.read(src);
    color = Scalar(0,0,255);
    coor_num = 0;
    xmlPath="C:/myregion.xml";
    cv::namedWindow("imageWindow", CV_WINDOW_AUTOSIZE );
    cv::imshow("imageWindow", src);
    cv::setMouseCallback( "imageWindow", onMouse, 0 );
    cv::waitKey(0);

}

void Settings::onMouse(int event, int x, int y, int, void* ) {
    if (event == CV_EVENT_LBUTTONUP) {
        Point2f p(x, y);
        coor.push_back(p);
        line(src,p,p,color);
        if(coor.size()>1)
            line(src, p, coor[coor.size()-2], color);
        imshow("imageWindow", src);
    }
    else if (event == CV_EVENT_RBUTTONUP && coor.size()>2){
        line(src, coor[0], coor[coor.size()-1], color);
        getPointsInContour(coor);
        imshow("imageWindow", src);
        waitKey(2000);
        exit(0);
    }
}
void Settings::savePointsAsXML(vector<Point2f> & contour){
    TiXmlDocument doc;
    TiXmlDeclaration decl("1.0", "", "");
    doc.InsertEndChild(decl);
    for(int i = 0; i < contour.size(); i++)
    {
        TiXmlElement point("point");
        point.SetAttribute("x",contour[i].x);
        point.SetAttribute("y",contour[i].y);
        doc.InsertEndChild(point);
    }
    if(doc.SaveFile(xmlPath.c_str()))
        cout << "file saved succesfully.\n";
    else
        cout << "file not saved, something went wrong!\n";
}

void Settings::getPointsInContour(vector<Point2f> & contour){
    vector<Point2f> insideContour;
    for(int j = 0; j < src.rows; j++){
        for(int i = 0; i < src.cols; i++){
            Point2f p(i,j);
            if(cv::pointPolygonTest(contour,p,false) >= 0) // yes inside
                insideContour.push_back(p);
        }
    }
    cout << "# points inside contour: " << insideContour.size() << endl;
    savePointsAsXML(insideContour);
}

我收到了大量对 Settings:coor、Settings:src、Settings:color 的 undefined reference 。我无法理解什么需要静态才能工作。这是我的标题:

class Settings
{
private:        
    static void onMouse(int event, int x, int y, int, void* );
    static void savePointsAsXML(std::vector<cv::Point2f> & contour);
    static void getPointsInContour(std::vector<cv::Point2f> & contour);
    static cv::Scalar color;
    static std::vector<cv::Point2f> coor;
    static int coor_num;
    static std::string xmlPath;
    static cv::Mat src;

我的代码中缺少什么？

Answer 1

由于 OpenCV 有一个类似 C 的接口(interface)，它不采用成员函数作为回调，但您可以使用标准方法来克服这个问题，并将类实例作为 userdata 参数传递，然后将其转换回去到实例并调用成员方法。这是一个片段:

void Settings::on_buttonXML_clicked(){
    cv::VideoCapture webcam;
    webcam.open(INDEX);    
    webcam.read(src);
    color = Scalar(0,0,255);
    coor_num = 0;
    xmlPath="C:/myregion.xml";
    cv::namedWindow("imageWindow", CV_WINDOW_AUTOSIZE );
    cv::imshow("imageWindow", src);
    cv::setMouseCallback( "imageWindow", onMouse, this ); // Pass the class instance pointer here
    cv::waitKey(0);
}

// In you header make a static and a member version of onMouse
void onMouse(int event, int x, int y);
static void onMouse(int event, int x, int y, int, void* userdata);

// Implement it to call the member function
void Settings::onMouse(int event, int x, int y, int, void* userdata)
{
    // Check for null pointer in userdata and handle the error
    ...
    Settings* settings = reinterpret_cast<Settings*>(userdata);
    settings->onMouse(event, x, y);
}

希望这能解释这个想法，我是内联写的，所以对于任何拼写错误我深表歉意。