import sys
from PySide6.QtGui import *
from PySide6.QtCore import *
from PySide6.QtWidgets import *


class MainWindow(QMainWindow):
    def __init__(self) -> None:
        super().__init__()
        self.label = QLabel()
        self.label.setPixmap(QPixmap(400, 300))
        self.setCentralWidget(self.label)

    def mouseMoveEvent(self, event: QMouseEvent) -> None:
        painter = QPainter(self.label.pixmap())
        painter.drawPoint(event.position())
        self.update()
        painter.end()
        del painter


if __name__ == "__main__":
    app = QApplication([])
    demo = MainWindow()
    demo.show()
    sys.exit(app.exec())