yolo中的目标检测 做个记录，方便后续理解

https://github.com/Wulingtian/yolov5_tensorrt_int8/blob/master/yolov5s_infer.cc

void nms_cpu(std::vector<Bbox> &bboxes, float threshold) {
    if (bboxes.empty()){
        return ;
    }
    // 1.之前需要按照score排序
    std::sort(bboxes.begin(), bboxes.end(), [&](Bbox b1, Bbox b2){return b1.score>b2.score;});
    // 2.先求出所有bbox自己的大小
    std::vector<float> area(bboxes.size());
    for (int i=0; i<bboxes.size(); ++i){
        area[i] = (bboxes[i].xmax - bboxes[i].xmin + 1) * (bboxes[i].ymax - bboxes[i].ymin + 1);
    }
    // 3.循环
    for (int i=0; i<bboxes.size(); ++i){
        for (int j=i+1; j<bboxes.size(); ){
            float left = std::max(bboxes[i].xmin, bboxes[j].xmin);
            float right = std::min(bboxes[i].xmax, bboxes[j].xmax);
            float top = std::max(bboxes[i].ymin, bboxes[j].ymin);
            float bottom = std::min(bboxes[i].ymax, bboxes[j].ymax);
            float width = std::max(right - left + 1, 0.f);
            float height = std::max(bottom - top + 1, 0.f);
            float u_area = height * width;
            float iou = (u_area) / (area[i] + area[j] - u_area);
            if (iou>=threshold){
                bboxes.erase(bboxes.begin()+j);
                area.erase(area.begin()+j);
            }else{
                ++j;
            }
        }
    }
}