点多边形测试
    测试一个点是否在给定的多边形内部，边缘或者外部

 

double pointPolygonTest(
    InputArray  contour,    // 输入的轮廓
    Point2f  pt,             // 测试点
    bool  measureDist         // 是否返回距离值，如果是false，1表示在内面，0表示在边界上，-1表示在外部，true返回实际距离
)

  

步骤
    构建一张400x400大小的图片， Mat::Zero(400, 400, CV_8UC1)
    画上一个六边形的闭合区域line
    发现轮廓
    对图像中所有像素点做点 多边形测试，得到距离，归一化后显示。

 

int main(int argc, char** argv) {
    const int r = 100;
    Mat src = Mat::zeros(r * 4, r * 4, CV_8UC1);

    vector<Point2f> vert(6);
    vert[0] = Point(3 * r / 2, static_cast<int>(1.34*r));
    vert[1] = Point(1 * r, 2 * r);
    vert[2] = Point(3 * r / 2, static_cast<int>(2.866*r));
    vert[3] = Point(5 * r / 2, static_cast<int>(2.866*r));
    vert[4] = Point(3 * r, 2 * r);
    vert[5] = Point(5 * r / 2, static_cast<int>(1.34*r));

    for (int i = 0; i < 6; i++) {
        line(src, vert[i], vert[(i + 1) % 6], Scalar(255), 3, 8, 0);
    }
    // 画一个六边型
    imshow("input_win", src);


    vector<vector<Point>> contours;
    vector<Vec4i> hierachy;
    Mat csrc;
    src.copyTo(csrc);
    //边界发现
    findContours(csrc, contours, hierachy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0));
    Mat raw_dist = Mat::zeros(csrc.size(), CV_32FC1);
    for (int row = 0; row < raw_dist.rows; row++) {
        for (int col = 0; col < raw_dist.cols; col++) {
            double dist = pointPolygonTest(contours[0], Point2f(static_cast<float>(col), static_cast<float>(row)), true);
            raw_dist.at<float>(row, col) = static_cast<float>(dist);
        }
    }

    double minValue, maxValue;
    minMaxLoc(raw_dist, &minValue, &maxValue, 0, 0, Mat());
    Mat drawImg = Mat::zeros(src.size(), CV_8UC3);
    for (int row = 0; row < drawImg.rows; row++) {
        for (int col = 0; col < drawImg.cols; col++) {
            float dist = raw_dist.at<float>(row, col);
            if (dist > 0) {
                //内部
                drawImg.at<Vec3b>(row, col)[0] = (uchar)(abs(1.0 - (dist / maxValue)) * 255);
            }
            else if (dist < 0) {
                //外部
                drawImg.at<Vec3b>(row, col)[2] = (uchar)(abs(1.0 - (dist / minValue)) * 255);
            }
            else {
                //边缘
                drawImg.at<Vec3b>(row, col)[0] = (uchar)(abs(255 - dist));
                drawImg.at<Vec3b>(row, col)[1] = (uchar)(abs(255 - dist));
                drawImg.at<Vec3b>(row, col)[2] = (uchar)(abs(255 - dist));
            }
        }
    }
    
    imshow("output_win", drawImg);

    waitKey(0);
    return 0;
}