一、源码

template<typename _Tp> class Rect_
{
public:
    typedef _Tp value_type;

    //! default constructor
    Rect_();
    Rect_(_Tp _x, _Tp _y, _Tp _width, _Tp _height);
    Rect_(const Rect_& r);
    Rect_(Rect_&& r) CV_NOEXCEPT;
    Rect_(const Point_<_Tp>& org, const Size_<_Tp>& sz);
    Rect_(const Point_<_Tp>& pt1, const Point_<_Tp>& pt2);

    Rect_& operator = ( const Rect_& r );
    Rect_& operator = ( Rect_&& r ) CV_NOEXCEPT;
    //! the top-left corner
    Point_<_Tp> tl() const;
    //! the bottom-right corner
    Point_<_Tp> br() const;

    //! size (width, height) of the rectangle
    Size_<_Tp> size() const;
    //! area (width*height) of the rectangle
    _Tp area() const;
    //! true if empty
    bool empty() const;

    //! conversion to another data type
    template<typename _Tp2> operator Rect_<_Tp2>() const;

    //! checks whether the rectangle contains the point
    bool contains(const Point_<_Tp>& pt) const;

    _Tp x; //!< x coordinate of the top-left corner
    _Tp y; //!< y coordinate of the top-left corner
    _Tp width; //!< width of the rectangle
    _Tp height; //!< height of the rectangle
};

typedef Rect_<int> Rect2i;
typedef Rect_<float> Rect2f;
typedef Rect_<double> Rect2d;
typedef Rect2i Rect;

Rect_是一个模板类，矩形由点、长和宽基本属性组成，opencv内部通过
typedef关键字分别以int 、float 和double三种基础类型命名了模板类Rect_的类型别名Rect2i，Rect2f，Rect2d，而Rect又是Rect2i 的类型别名。

二、cv::Rect的成员和属性

1.成员

    rect.tl()//矩形左上角点的坐标
    rect.br()//矩形右下角点的坐标
    rect.size()//矩形的大小
    rect.area()//矩形的面积
    rect.empty() //判断矩形是否为空
    rect.contains() //判断一个点是否在矩形区域内

2.属性

    rect.x; //表示左上角点x的坐标
    rect.y; //表示左上角点y的坐标
    rect.width; //表示矩形的宽度
    rect.height; //表示矩形的高度

三、代码示例

void test_Rect()
{
    cv::Mat src;
      src = cv::imread("D:\\QtProject\\Opencv_Example\\rect\\rect.jpg", cv::IMREAD_COLOR);
      if (src.empty()) {
          cout << "Cannot load image" << endl;
          return;
      }
    //show(src);


    // 绘制矩形框
    cv::Rect rect1(60, 60, 200, 400);
    cv::rectangle(src, rect1, cv::Scalar(0, 0, 0), 1, 8, 0);


    // tl(): 矩形左上角点的坐标    br():矩形右下角点的坐标
    cv::circle(src, rect1.tl(), 3, cv::Scalar(0, 255, 255), 3, 8, 0);
    cv::circle(src, rect1.br(), 3, cv::Scalar(0, 255, 255), 3, 8, 0);

    // 判定一个点是否在矩形内
    cv::Point pt1(100, 200);
    cv::Point pt2(459, 450);
    cv::circle(src, pt1, 3, cv::Scalar(0, 0, 255), 3, 8, 0);
    cv::circle(src, pt2, 3, cv::Scalar(0, 0, 255), 3, 8, 0);

    qDebug()<< "pt1 in r1: " << rect1.contains(pt1) << " pt2 in r1: " << rect1.contains(pt2) <<'\t';
    qDebug()<< "rect1 area: " << rect1.area() << " rect1 size: " << rect1.size().height<<"X"<<rect1.size().width<<'\t';


    // 平移rect1 到 movePt
    cv::Point movePt(0, 500);  //向Y轴移动500
    cv::Rect rect2 = rect1 + movePt;
    // tl(): 矩形左上角点的坐标    br():矩形右下角点的坐标
    cv::circle(src, rect2.tl(), 3, cv::Scalar(0, 0, 0), 3, 8, 0);
    cv::circle(src, rect2.br(), 3, cv::Scalar(0, 0, 0), 3, 8, 0);
    cv::rectangle(src, rect2, cv::Scalar(0, 0, 255), 2, 8, 0);

    //比较两个矩形
    std::cout << "rect1 == rect2: "<< std::to_string(rect1 == rect2);

    //求两个矩形的并
    cv::Rect rect3 = rect1 | rect2;
    cv::Point movePt2(300, 0);  //向Y轴移动500
    cv::Rect rect4 = rect3 + movePt2;
    cv::rectangle(src, rect4, cv::Scalar(0, 255, 0), 2, 8, 0);

    imshow("src",src);
    //排序矩形
    //std::vector<cv::Rect> Rect;
    //Rect.push_back(rect1);
    //Rect.push_back(rect2);
    //Rect.push_back(rect3);

    //std::sort(Rect.begin(), Rect.end(), compareRect_y);
    //for (cv::Rect rect : Rect) {
    //std::cout << "sorted rect: "<<rect.tl() << " rect.area: " << rect.area()<<std::endl;
    //}


}

四、运行效果