PyQt5 在label显示的图片中绘制矩形的方法

from PyQt5.QtWidgets import QWidget, QApplication, QLabelfrom PyQt5.QtCore import QRect, Qtfrom PyQt5.QtGui import QImage, QPixmap, QPainter, QPen, QGuiApplicationimport cv2import sysclass MyLabel(QLabel): x0 = 0 y0 = 0 x1 = 0 y1 = 0 flag = False #鼠标点击事件 def mousePressEvent(self,event):  self.flag = True  self.x0 = event.x()  self.y0 = event.y() #鼠标释放事件 def mouseReleaseEvent(self,event):  self.flag = False #鼠标移动事件 def mouseMoveEvent(self,event):  if self.flag:   self.x1 = event.x()   self.y1 = event.y()   self.update() #绘制事件 def paintEvent(self, event):  super().paintEvent(event)  rect =QRect(self.x0, self.y0, abs(self.x1-self.x0), abs(self.y1-self.y0))  painter = QPainter(self)  painter.setPen(QPen(Qt.red,2,Qt.SolidLine))  painter.drawRect(rect)class Example(QWidget): def __init__(self):  super().__init__()  self.initUI() def initUI(self):  self.resize(675, 300)  self.setWindowTitle('在label中绘制矩形')  self.lb = MyLabel(self) #重定义的label  self.lb.setGeometry(QRect(30, 30, 511, 541))  img = cv2.imread('2.jpg')  height, width, bytesPerComponent = img.shape  bytesPerLine = 3 * width  cv2.cvtColor(img, cv2.COLOR_BGR2RGB, img)  QImg = QImage(img.data, width, height, bytesPerLine,QImage.Format_RGB888)  pixmap = QPixmap.fromImage(QImg)  self.lb.setPixmap(pixmap)  self.lb.setCursor(Qt.CrossCursor)  self.show()if __name__ == '__main__': app = QApplication(sys.argv) x = Example() sys.exit(app.exec_())