QGraphicsProxyWidget messes up mouse cursor changes

Question

I have a QGraphicsView where I do various mouse operations and while doing mouse operations I change mouse cursor to give user visual clues.

I recently put some QWidgets onto my scene which automatically creates QGraphicsProxyWidget objects. And after putting these widgets I started having problems with my mouse cursor changes. I can change mouse cursor until I hover over a QGraphicsProxyWidget item. After that, my mouse cursor changes stop taking effect.

I created a minimal example in PySide2:

import sys

from PySide2.QtGui import QMouseEvent, Qt
from PySide2.QtWidgets import QApplication, QLabel, QGraphicsView, QGraphicsScene


class CustomGraphicsView(QGraphicsView):
    def mousePressEvent(self, event: QMouseEvent):
        super().mousePressEvent(event)

        self.setCursor(Qt.ClosedHandCursor)
        event.accept()

    def mouseReleaseEvent(self, event: QMouseEvent):
        super().mouseReleaseEvent(event)

        self.setCursor(Qt.ArrowCursor)
        event.accept()


if __name__ == "__main__":
    app = QApplication(sys.argv)
    graphics_view = CustomGraphicsView()
    scene = QGraphicsScene(0, 0, 1000, 1000)
    graphics_view.setScene(scene)

    label = QLabel("Hello World")
    label_font = label.font()
    label_font.setPointSize(50)
    label.setFont(label_font)

    label_proxy = scene.addWidget(label)
    label_proxy.setPos(400, 450)

    graphics_view.show()
    app.exec_()

To reproduce: first, click on anywhere in the scene without hovering your mouse over the "Hello World" text. You will see mouse cursor changing into a closed hand. Then hover your mouse over "Hello World" text and try again clicking anywhere on scene. You will see that the cursor is not changing anymore.

I am not sure if this is an expected behavior or bug. What might be the reason for this behavior?

System

OS: Windows 10 20H2

Python 3.8.6 64-bit

PySide2 5.15.2

user_6622587 · Answer

_{Disclaimer: Still investigating the cause of that behavior so at the time of writing this answer I will only give the solution. But it seems is that the propagation of the events is not handled correctly by the QGraphicsProxyWidget. See this bug for more information.}

Instead of setting the cursor in the QGraphicsView it should be set in the viewport.

class CustomGraphicsView(QGraphicsView):
    def mousePressEvent(self, event: QMouseEvent):
        super().mousePressEvent(event)
        self.viewport().setCursor(Qt.ClosedHandCursor)
        event.accept()

    def mouseReleaseEvent(self, event: QMouseEvent):
        super().mouseReleaseEvent(event)
        self.viewport().unsetCursor()
        event.accept()

QGraphicsProxyWidget messes up mouse cursor changes

System

1 Answers