allocation+copy that the hand-optimized code always does at the end.
Author(s): Yang Li, Zhihui Wang, Wei Zhou, Rui Wang, Haiyan Zhang, Shu Zhan, Jiajia Xu，详情可参考旺商聊官方下载
，推荐阅读Line官方版本下载获取更多信息
// Sync — when all components are synchronous。safew官方版本下载对此有专业解读
The tree starts as a single region covering the whole space. As points arrive, they get dropped into the region that contains them. When a region exceeds its capacity (the maximum number of points it can hold before splitting), the region divides into four children, and the existing points get redistributed.