Qt Bug Report: setCursor() Stops Working & Hover Event Issue

📝 Overview

This repository contains a minimal example to demonstrate two Qt bugs:

1. Hover event does not trigger in a ~10px area at the bottom edge of a RectItem
2. setCursor() stops working after interacting with a messagebox using the keyboard

🛠 Environment

• Qt Version: 6.8.2
• OS: macOS Sequoia 15.3.2
• Compiler: Apple Clang 16.0.0 (clang-1600.0.26.6)

🔧 Build & Run Instructions

git clone https://github.com/eKevinHoang/QGraphicsBug.git
cd QGraphicsBug
mkdir build
cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug
cmake --build build --config Debug
./build/QGraphicsBug

🚀 Steps to Reproduce

Bug 1: Hover event does not trigger in a ~10px area at the bottom edge of RectItem

1. Run the app. (See Build Instructions above.)
2. Move the mouse to the edges of the pre-drawn RectItem objects and observe the cursor.
   • ✅ Expected: The cursor changes correctly based on ResizeDirection.
3. Zoom in and out freely using the mouse wheel. (Do not move or resize the application window.)
4. Move the mouse again to the edges of the RectItem objects.
   • ❌ Issue: The bottom ~10px region does not trigger hover events. Even debug messages inside hoverMoveEvent() do not appear.

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Bug 2: setCursor() stops working after interacting with a messagebox

1. Start from step 1 of Bug 1, or launch the app normally.
2. Pan the image by holding Command and dragging the mouse.
   • ✅ Expected: The cursor should change to a hand cursor (Qt::OpenHandCursor) while panning.
3. Right click to trigger a messagebox.
4. Interact with the messagebox using the keyboard (e.g., press Space or Tab to navigate buttons).
5. Try panning the image again.
   • ❌ Issue: The cursor remains stuck as an arrow (Qt::ArrowCursor), even after clicking on the scene 🔹 Note: This issue does not always occur, but it is fairly easy to reproduce.
     🔹 Hypothesis: This may be due to a Qt UI thread synchronization issue when handling cursor updates after modal dialogs.

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