Image not showing while trying to draw a rectangle over a PyQt QLabel

Question

Image does not show up when trying to draw a rectangle over QLabel image. I want to be able to draw a rectangle over the photo and be able to keep the rectangle/hide it. Here's what I tried after checking suggestions here:

• How to draw a rectangle and adjust its shape by drag and drop in PyQt5

from PyQt5.QtGui import QPixmap, QImage, QPainter, QBrush, QColor
from PyQt5.QtWidgets import QMainWindow, QApplication, QDesktopWidget, QVBoxLayout, QWidget, QLabel
from PyQt5.QtCore import QPoint, QRect
import sys
import cv2


class TestRect(QLabel):
    def __init__(self):
        super().__init__()
        self.begin = QPoint()
        self.end = QPoint()

    def paintEvent(self, event):
        qp = QPainter(self)
        br = QBrush(QColor(100, 10, 10, 40))
        qp.setBrush(br)
        qp.drawRect(QRect(self.begin, self.end))

    def mousePressEvent(self, event):
        self.begin = event.pos()
        self.end = event.pos()
        self.update()

    def mouseMoveEvent(self, event):
        self.end = event.pos()
        self.update()

    def mouseReleaseEvent(self, event):
        self.begin = event.pos()
        self.end = event.pos()
        self.update()


class TestWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.current_image = None
        win_rectangle = self.frameGeometry()
        center_point = QDesktopWidget().availableGeometry().center()
        win_rectangle.moveCenter(center_point)
        self.move(win_rectangle.topLeft())
        self.main_layout = QVBoxLayout()
        self.central_widget = QWidget(self)
        self.test_image()
        self.show()

    def test_image(self):
        self.central_widget.setLayout(self.main_layout)
        self.setCentralWidget(self.central_widget)
        image = TestRect()
        self.main_layout.addWidget(image)
        uploaded = cv2.imread('test.jpg')
        resized = cv2.resize(uploaded, (500, 500))
        height, width = 500, 500
        self.current_image = QImage(resized, height, width, QImage.Format_RGB888)
        image.setPixmap(QPixmap(self.current_image))


if __name__ == '__main__':
    test = QApplication(sys.argv)
    test_window = TestWindow()
    sys.exit(test.exec_())

Answer 1

If you override a method without calling the parent's implementation through super then the previous behavior will not be used, and that is what happens in your case: The normal behavior of QLabel is to draw but to override and not to call super it was eliminated . The solution is:

def paintEvent(self, event):
    
    qp = QPainter(self)
    br = QBrush(QColor(100, 10, 10, 40))
    qp.setBrush(br)
    qp.drawRect(QRect(self.begin, self.end))