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  1. Qt
  2. QTBUG-80176

Disable 'Mirror Displays' on macOS causes all running Qt applications to crash

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: P2: Important
    • Resolution: Done
    • Affects Version/s: 5.13.1
    • Fix Version/s: 5.14.0 RC1
    • Component/s: QPA
    • Environment:
      macOS 10.15.1
      Qt 5.13.1

      Description

      Description

      When you disable the 'Mirror Displays' checkbox on macOS, all running Qt applications are crashing. See attached video to see Qt Creator crashing.

       

      Reproducibility

      • This issue is reproducible with Qt 5.13.1 on macOS 10.15.1

       

      Steps to reproduce

      1. Attach an external display to a Mac (tested with iMac and MacBook Pro). I used a Thunderbolt Dock and Display Port to connect the external display.
      2. Launch any Qt application on the external screen. For example Qt Creator.
      3. Open System Preferences > Displays > Arrangement
      4. Check "Mirror Displays" if it is not checked
      5. Uncheck "Mirror Displays"

      Result: All running Qt applications (for example Qt Creator) are crashing

      Qt Support has tested and confirms the crash.

       

       

      More info

       The crash occurs in QCocoaScreen::initializeScreens() in qcocoascreen.mm.

      As you can see in this code, there is no check for NULL pointer for the variable mainDisplay and cocoaScreen:

                  // Detect changes to the primary screen immediately, instead of
                  // waiting for a display reconfigure with kCGDisplaySetMainFlag.
                  // This ensures that any property updates to the other screens
                  // will be in reference to the correct primary screen.
                  QCocoaScreen *mainDisplay = QCocoaScreen::get(CGMainDisplayID());
                  if (QGuiApplication::primaryScreen()->handle() != mainDisplay) {
                      mainDisplay->updateProperties();
                      qCInfo(lcQpaScreen) << "Primary screen changed to" << mainDisplay;
                      QWindowSystemInterface::handlePrimaryScreenChanged(mainDisplay);
                  }
      
                  if (cocoaScreen == mainDisplay)
                      return; // Already reconfigured
      
                  cocoaScreen->updateProperties();
                  qCInfo(lcQpaScreen) << "Reconfigured" << cocoaScreen;
      

      If the variables mainDisplay or cocoaScreen are NULL - which is what seems to be the case when disabling "Mirror Displays" - the application is crashing.

       

       

       

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            Assignee:
            vestbo Tor Arne Vestbø
            Reporter:
            timaccorsair Alexandre Colucci
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              Dates

              Created:
              Updated:
              Resolved:

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