Add QPlatformWindow::initialize() for two-step window creation

The QWindow::create method calls createPlatformWindow, and assigns the
result to d->platformWindow. If the platform sends any sort of events
synchronously during the creation, the event will be delivered to a
QWindow that doesn't have a handle() yet, resulting in noop handling
of the event, or crashes.

To mitigate this situations, platforms should do as little a possible
in the QPlatformWindow constructor, and leave initialization to the
new method, where the QWindow will have a handle().

The macOS platform plugin still has a m_initialized guard, to prevent
sending geometry changes during initialization, as this will result
in a resize event before a show event. This forced behavior seems
dubious, but is left for a followup patch.

Task-number: QTBUG-61977
Change-Id: I04d32d93391e89d068752b719270438e7024ad46
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

src/gui/kernel/qplatformwindow.cpp

@@ -70,6 +70,17 @@ QPlatformWindow::~QPlatformWindow()
 {
 }
 
+/*!
+    Called as part of QWindow::create(), after constructing
+    the window. Platforms should prefer to do initialization
+    here instead of in the constructor, as the platform window
+    object will be fully constructed, and associated to the
+    corresponding QWindow, allowing synchronous event delivery.
+*/
+void QPlatformWindow::initialize()
+{
+}
+
 /*!
     Returns the window which belongs to the QPlatformWindow
 */

src/gui/kernel/qplatformwindow.h

@@ -74,6 +74,8 @@ public:
     explicit QPlatformWindow(QWindow *window);
     virtual ~QPlatformWindow();
 
+    virtual void initialize();
+
     QWindow *window() const;
     QPlatformWindow *parent() const;
 

src/gui/kernel/qwindow.cpp

@@ -509,6 +509,8 @@ void QWindowPrivate::create(bool recursive, WId nativeHandle)
         return;
     }
 
+    platformWindow->initialize();
+
     QObjectList childObjects = q->children();
     for (int i = 0; i < childObjects.size(); i ++) {
         QObject *object = childObjects.at(i);

src/plugins/platforms/cocoa/qcocoawindow.h

@@ -95,6 +95,8 @@ public:
     QCocoaWindow(QWindow *tlw, WId nativeHandle = 0);
     ~QCocoaWindow();
 
+    void initialize() override;
+
     void setGeometry(const QRect &rect) Q_DECL_OVERRIDE;
     QRect geometry() const Q_DECL_OVERRIDE;
     void setCocoaGeometry(const QRect &rect);
@@ -250,7 +252,7 @@ public: // for QNSView
     QPointer<QWindow> m_enterLeaveTargetWindow;
     bool m_windowUnderMouse;
 
-    bool m_inConstructor;
+    bool m_initialized;
     bool m_inSetVisible;
     bool m_inSetGeometry;
     bool m_inSetStyleMask;

src/plugins/platforms/cocoa/qcocoawindow.mm

@@ -132,8 +132,8 @@ Q_CONSTRUCTOR_FUNCTION(qRegisterNotificationCallbacks)
 
 const int QCocoaWindow::NoAlertRequest = -1;
 
-QCocoaWindow::QCocoaWindow(QWindow *tlw, WId nativeHandle)
-    : QPlatformWindow(tlw)
+QCocoaWindow::QCocoaWindow(QWindow *win, WId nativeHandle)
+    : QPlatformWindow(win)
     , m_view(nil)
     , m_nsWindow(0)
     , m_viewIsEmbedded(false)
@@ -141,7 +141,7 @@ QCocoaWindow::QCocoaWindow(QWindow *tlw, WId nativeHandle)
     , m_lastReportedWindowState(Qt::WindowNoState)
     , m_windowModality(Qt::NonModal)
     , m_windowUnderMouse(false)
-    , m_inConstructor(true)
+    , m_initialized(false)
     , m_inSetVisible(false)
     , m_inSetGeometry(false)
     , m_inSetStyleMask(false)
@@ -165,24 +165,31 @@ QCocoaWindow::QCocoaWindow(QWindow *tlw, WId nativeHandle)
 {
     qCDebug(lcQpaCocoaWindow) << "QCocoaWindow::QCocoaWindow" << window();
 
-    QMacAutoReleasePool pool;
-
     if (nativeHandle) {
         m_view = reinterpret_cast<NSView *>(nativeHandle);
         [m_view retain];
-    } else {
+    }
+}
+
+void QCocoaWindow::initialize()
+{
+    qCDebug(lcQpaCocoaWindow) << "QCocoaWindow::initialize" << window();
+
+    QMacAutoReleasePool pool;
+
+    if (!m_view) {
         m_view = [[QNSView alloc] initWithCocoaWindow:this];
         // Enable high-dpi OpenGL for retina displays. Enabling has the side
         // effect that Cocoa will start calling glViewport(0, 0, width, height),
         // overriding any glViewport calls in application code. This is usually not a
         // problem, except if the appilcation wants to have a "custom" viewport.
         // (like the hellogl example)
-        if (tlw->supportsOpenGL()) {
-            BOOL enable = qt_mac_resolveOption(YES, tlw, "_q_mac_wantsBestResolutionOpenGLSurface",
+        if (window()->supportsOpenGL()) {
+            BOOL enable = qt_mac_resolveOption(YES, window(), "_q_mac_wantsBestResolutionOpenGLSurface",
                                                           "QT_MAC_WANTS_BEST_RESOLUTION_OPENGL_SURFACE");
             [m_view setWantsBestResolutionOpenGLSurface:enable];
         }
-        BOOL enable = qt_mac_resolveOption(NO, tlw, "_q_mac_wantsLayer",
+        BOOL enable = qt_mac_resolveOption(NO, window(), "_q_mac_wantsLayer",
                                                      "QT_MAC_WANTS_LAYER");
         [m_view setWantsLayer:enable];
     }
@@ -190,10 +197,11 @@ QCocoaWindow::QCocoaWindow(QWindow *tlw, WId nativeHandle)
     setGeometry(initialGeometry(window(), windowGeometry(), defaultWindowWidth, defaultWindowHeight));
 
     recreateWindowIfNeeded();
-    tlw->setGeometry(geometry());
-    if (tlw->isTopLevel())
-        setWindowIcon(tlw->icon());
-    m_inConstructor = false;
+    window()->setGeometry(geometry());
+    if (window()->isTopLevel())
+        setWindowIcon(window()->icon());
+
+    m_initialized = true;
 }
 
 QCocoaWindow::~QCocoaWindow()
@@ -1021,8 +1029,10 @@ bool QCocoaWindow::windowShouldClose()
 
 void QCocoaWindow::handleGeometryChange()
 {
-    // Don't send geometry change event to Qt unless it's ready to handle events
-    if (m_inConstructor)
+    // Prevent geometry change during initialization, as that will result
+    // in a resize event, and Qt expects those to come after the show event.
+    // FIXME: Remove once we've clarified the Qt behavior for this.
+    if (!m_initialized)
         return;
 
     // Don't send the geometry change if the QWindow is designated to be