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  1. Qt
  2. QTBUG-93182

Occasional asserts when touch scroll NSEventPhaseEnded is processed while event in queue indicates momentumPhase has begun



    • macOS


      A customer is receiving rare cases where when QNSView mouse scrollWheel method is invoked with it's event phase set to NSEventPhaseEnded, and a look through the event queue finds another scroll wheel event with momentumPhase set to NSEventPhaseBegan, but where the assumption is broken in this case - that momentum scroll wheel event contains nonzero pixelDelta or nonzero angleDelta.

      It doesn't seem to matter which scroll area is scrolled - it has been reproduced in 2-3 entirely different areas of the application. As this is so rare, it has not been reproduced in a simple Qt example (it seems to only occur on the order of once a month a so of active use of the Qt 5.15.2-based application)

      The assertion happens at src/plugins/platforms/cocoa/qnsview_mouse.mm:654.

      As this is a Q_ASSERT, it only occurs when the application is compiled debug, so end customers are not affected, however, the customer was wondering why this was a fatal error (causing the application to stop), rather than just logged.

      The customer has a macBook Pro and a Magic Mouse, and uses both. He's not clear if the reproduction occurs with one or the other of those input devices. He also uses something called MagicPrefs which I see has not been maintained for some years, and uses deprecated and reverse-engineered private Apple APIs - I wonder if it may be affecting this.

      Here is a backtrace showing this assert in Qt 5.15.2:

      ASSERT: "pixelDelta.isNull() && angleDelta.isNull()" in file /local/S/workspace/qt_maya/src/qtbase/src/plugins/platforms/cocoa/qnsview_mouse.mm, line 658
      Stack trace:
        4   libsystem_kernel.dylib              0x00007fff6b76833a __pthread_kill + 10
        5   libsystem_c.dylib                   0x00007fff6b6ef808 abort + 120
        6   libQt5Core_debug.5.15.2.dylib       0x0000000127a1d0d8 qt_message_fatal(QtMsgType, QMessageLogContext const&, QString const&) + 24
        7   libQt5Core_debug.5.15.2.dylib       0x0000000127a1f52e QMessageLogger::fatal(char const*, ...) const + 446
        8   libQt5Core_debug.5.15.2.dylib       0x0000000127a136f7 qt_assert(char const*, char const*, int) + 87
        9   libqcocoa_debug.dylib               0x0000000176bec548 -[QNSView(Mouse) scrollWheel:] + 1336
        10  AppKit                              0x00007fff2e997d5d -[NSWindow(NSEventRouting) _reallySendEvent:isDelayedEvent:] + 6512
        11  AppKit                              0x00007fff2e9961c9 -[NSWindow(NSEventRouting) sendEvent:] + 349
        12  libqcocoa_debug.dylib               0x0000000176bfbe0c -[QNSPanel sendEvent:] + 764
        13  AppKit                              0x00007fff2e994d36 -[NSApplication(NSEvent) sendEvent:] + 2370
        14  libqcocoa_debug.dylib               0x0000000176c0635c -[QNSApplication sendEvent:] + 76
        15  AppKit                              0x00007fff2eaf1f3b -[NSApplication _doModalLoop:peek:] + 388
        16  AppKit                              0x00007fff2ec8440c __33-[NSApplication runModalSession:]_block_invoke_2 + 69
        17  AppKit                              0x00007fff2ec843b4 __33-[NSApplication runModalSession:]_block_invoke + 78
        18  AppKit                              0x00007fff2eaf04c4 _NSTryRunModal + 100
        19  AppKit                              0x00007fff2ec842af -[NSApplication runModalSession:] + 128
        20  libqcocoa_debug.dylib               0x0000000176bff83a QCocoaEventDispatcher::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) + 650
        21  libQt5Core_debug.5.15.2.dylib       0x0000000127d3bdc7 QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) + 119
        22  libQt5Core_debug.5.15.2.dylib       0x0000000127d3bfee QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) + 526
        23  libQt5Widgets_debug.5.15.2.dylib    0x00000001240833af QDialog::exec() + 367
        24  libSharedUI.dylib                   0x000000010c0345a8 (anonymous namespace)::MayaDialog(TargParser&, QFileDialog::FileMode, QString const&, QString const&, QString const&, QString&, QStringList&, QFlags<QFileDialog::Option>) + 3704
        25  libSharedUI.dylib                   0x000000010c032d2c TmayaFileDialogCmd::doCommand(TargList&) + 1932

      This bug was introduced by feature linked with this issue: QTBUG-65160 : macOS: Teach QWheelEvent to handle a new ScrollMomentum phase


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            vestbo Tor Arne Vestbø
            kkyzivat Keith Kyzivat
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