参考资料：
https://blog.csdn.net/qq_35488967/article/details/70802973
https://blog.csdn.net/wanghualin033/article/details/78633604
https://blog.csdn.net/liang19890820/article/details/51393152
https://blog.csdn.net/liang19890820/article/details/51154216
https://www.cnblogs.com/jiangu66/archive/2013/05/12/3074852.html
https://www.cnblogs.com/Jace-Lee/p/5946342.html
QBrush定义了QPainter的填充模式，具有样式、颜色、渐变以及纹理等属性。