Merge remote-tracking branch 'origin/5.12' into 5.13

 Conflicts:
	src/gui/kernel/qplatformintegration.cpp
	src/gui/kernel/qplatformintegration.h
	src/plugins/platforms/wasm/qwasmintegration.cpp
	src/plugins/platforms/xcb/qxcbconnection_screens.cpp

Change-Id: I15063d42e9a1e226d9d2d2d372f75141b84c5c1b

69 files changed, 1164 insertions, 349 deletions

diff --git a/src/3rdparty/angle/src/libANGLE/Context.cpp b/src/3rdparty/angle/src/libANGLE/Context.cpp
index f638beda58..84f7936feb 100644
--- a/src/3rdparty/angle/src/libANGLE/Context.cpp
+++ b/src/3rdparty/angle/src/libANGLE/Context.cpp
@@ -451,7 +451,8 @@ egl::Error Context::onDestroy(const egl::Display *display)
 
     for (auto &zeroTexture : mZeroTextures)
     {
-        ANGLE_TRY(zeroTexture.second->onDestroy(this));
+        auto result = zeroTexture.second->onDestroy(this);
+        ANGLE_TRY(egl::Error(result));
         zeroTexture.second.set(this, nullptr);
     }
     mZeroTextures.clear();
diff --git a/src/3rdparty/angle/src/libANGLE/Stream.cpp b/src/3rdparty/angle/src/libANGLE/Stream.cpp
index 68279976b7..e384c7d486 100644
--- a/src/3rdparty/angle/src/libANGLE/Stream.cpp
+++ b/src/3rdparty/angle/src/libANGLE/Stream.cpp
@@ -192,8 +192,9 @@ Error Stream::consumerAcquire(const gl::Context *context)
     {
         if (mPlanes[i].texture != nullptr)
         {
-            ANGLE_TRY(mPlanes[i].texture->acquireImageFromStream(
-                context, mProducerImplementation->getGLFrameDescription(i)));
+            auto result = mPlanes[i].texture->acquireImageFromStream(
+                context, mProducerImplementation->getGLFrameDescription(i));
+            ANGLE_TRY(Error(result));
         }
     }
 
@@ -213,7 +214,8 @@ Error Stream::consumerRelease(const gl::Context *context)
     {
         if (mPlanes[i].texture != nullptr)
         {
-            ANGLE_TRY(mPlanes[i].texture->releaseImageFromStream(context));
+            auto result = mPlanes[i].texture->releaseImageFromStream(context);
+            ANGLE_TRY(Error(result));
         }
     }
 
diff --git a/src/3rdparty/angle/src/libANGLE/Texture.cpp b/src/3rdparty/angle/src/libANGLE/Texture.cpp
index da92e65916..7447604fe6 100644
--- a/src/3rdparty/angle/src/libANGLE/Texture.cpp
+++ b/src/3rdparty/angle/src/libANGLE/Texture.cpp
@@ -550,7 +550,8 @@ Error Texture::onDestroy(const Context *context)
 {
     if (mBoundSurface)
     {
-        ANGLE_TRY(mBoundSurface->releaseTexImage(context, EGL_BACK_BUFFER));
+        auto result = mBoundSurface->releaseTexImage(context, EGL_BACK_BUFFER);
+        ANGLE_TRY(Error(result));
         mBoundSurface = nullptr;
     }
     if (mBoundStream)
diff --git a/src/3rdparty/angle/src/libANGLE/renderer/d3d/d3d9/Renderer9.cpp b/src/3rdparty/angle/src/libANGLE/renderer/d3d/d3d9/Renderer9.cpp
index 75c6298868..b583273641 100644
--- a/src/3rdparty/angle/src/libANGLE/renderer/d3d/d3d9/Renderer9.cpp
+++ b/src/3rdparty/angle/src/libANGLE/renderer/d3d/d3d9/Renderer9.cpp
@@ -376,7 +376,8 @@ egl::Error Renderer9::initializeDevice()
 
     ASSERT(!mBlit);
     mBlit = new Blit9(this);
-    ANGLE_TRY(mBlit->initialize());
+    auto result = mBlit->initialize();
+    ANGLE_TRY(egl::Error(result));
 
     ASSERT(!mVertexDataManager && !mIndexDataManager);
     mVertexDataManager = new VertexDataManager(this);
diff --git a/src/angle/patches/0013-Fix-compilation-with-icc-converting-between-egl-s-an.patch b/src/angle/patches/0013-Fix-compilation-with-icc-converting-between-egl-s-an.patch
new file mode 100644
index 0000000000..6d3b1cac08
--- /dev/null
+++ b/src/angle/patches/0013-Fix-compilation-with-icc-converting-between-egl-s-an.patch
@@ -0,0 +1,93 @@
+From 2d8118620d4871f74a3ddca233529ff540384477 Mon Sep 17 00:00:00 2001
+From: Yuhang Zhao <2546789017@qq.com>
+Date: Wed, 13 Feb 2019 23:26:55 +0800
+Subject: [PATCH] Fix compilation with icc, converting between egl's and gl's
+ Error types
+
+Each has two constructors from the other, one copying the other
+moving; and this leads to an ambiguous overload when converting
+Texture::onDestroy()'s gl::error to the egl::Error that
+gl::Context::onDestroy() returns.  Passing the value through a
+temporary prevents the move-constructor from being attempted and saves
+the day.  Thanks to Ville Voutilainen for suggesting the fix.
+
+Fixes: QTBUG-73698
+Change-Id: I628173399a73cee2e253201bc3e8d3e6477a2fbf
+---
+ src/3rdparty/angle/src/libANGLE/Context.cpp               | 3 ++-
+ src/3rdparty/angle/src/libANGLE/Stream.cpp                | 8 +++++---
+ src/3rdparty/angle/src/libANGLE/Texture.cpp               | 3 ++-
+ .../angle/src/libANGLE/renderer/d3d/d3d9/Renderer9.cpp    | 3 ++-
+ 4 files changed, 11 insertions(+), 6 deletions(-)
+
+diff --git a/src/3rdparty/angle/src/libANGLE/Context.cpp b/src/3rdparty/angle/src/libANGLE/Context.cpp
+index f638beda58..84f7936feb 100644
+--- a/src/3rdparty/angle/src/libANGLE/Context.cpp
++++ b/src/3rdparty/angle/src/libANGLE/Context.cpp
+@@ -451,7 +451,8 @@ egl::Error Context::onDestroy(const egl::Display *display)
+ 
+     for (auto &zeroTexture : mZeroTextures)
+     {
+-        ANGLE_TRY(zeroTexture.second->onDestroy(this));
++        auto result = zeroTexture.second->onDestroy(this);
++        ANGLE_TRY(egl::Error(result));
+         zeroTexture.second.set(this, nullptr);
+     }
+     mZeroTextures.clear();
+diff --git a/src/3rdparty/angle/src/libANGLE/Stream.cpp b/src/3rdparty/angle/src/libANGLE/Stream.cpp
+index 68279976b7..e384c7d486 100644
+--- a/src/3rdparty/angle/src/libANGLE/Stream.cpp
++++ b/src/3rdparty/angle/src/libANGLE/Stream.cpp
+@@ -192,8 +192,9 @@ Error Stream::consumerAcquire(const gl::Context *context)
+     {
+         if (mPlanes[i].texture != nullptr)
+         {
+-            ANGLE_TRY(mPlanes[i].texture->acquireImageFromStream(
+-                context, mProducerImplementation->getGLFrameDescription(i)));
++            auto result = mPlanes[i].texture->acquireImageFromStream(
++                context, mProducerImplementation->getGLFrameDescription(i));
++            ANGLE_TRY(Error(result));
+         }
+     }
+ 
+@@ -213,7 +214,8 @@ Error Stream::consumerRelease(const gl::Context *context)
+     {
+         if (mPlanes[i].texture != nullptr)
+         {
+-            ANGLE_TRY(mPlanes[i].texture->releaseImageFromStream(context));
++            auto result = mPlanes[i].texture->releaseImageFromStream(context);
++            ANGLE_TRY(Error(result));
+         }
+     }
+ 
+diff --git a/src/3rdparty/angle/src/libANGLE/Texture.cpp b/src/3rdparty/angle/src/libANGLE/Texture.cpp
+index da92e65916..7447604fe6 100644
+--- a/src/3rdparty/angle/src/libANGLE/Texture.cpp
++++ b/src/3rdparty/angle/src/libANGLE/Texture.cpp
+@@ -550,7 +550,8 @@ Error Texture::onDestroy(const Context *context)
+ {
+     if (mBoundSurface)
+     {
+-        ANGLE_TRY(mBoundSurface->releaseTexImage(context, EGL_BACK_BUFFER));
++        auto result = mBoundSurface->releaseTexImage(context, EGL_BACK_BUFFER);
++        ANGLE_TRY(Error(result));
+         mBoundSurface = nullptr;
+     }
+     if (mBoundStream)
+diff --git a/src/3rdparty/angle/src/libANGLE/renderer/d3d/d3d9/Renderer9.cpp b/src/3rdparty/angle/src/libANGLE/renderer/d3d/d3d9/Renderer9.cpp
+index 75c6298868..b583273641 100644
+--- a/src/3rdparty/angle/src/libANGLE/renderer/d3d/d3d9/Renderer9.cpp
++++ b/src/3rdparty/angle/src/libANGLE/renderer/d3d/d3d9/Renderer9.cpp
+@@ -376,7 +376,8 @@ egl::Error Renderer9::initializeDevice()
+ 
+     ASSERT(!mBlit);
+     mBlit = new Blit9(this);
+-    ANGLE_TRY(mBlit->initialize());
++    auto result = mBlit->initialize();
++    ANGLE_TRY(egl::Error(result));
+ 
+     ASSERT(!mVertexDataManager && !mIndexDataManager);
+     mVertexDataManager = new VertexDataManager(this);
+-- 
+2.20.1.windows.1
+
diff --git a/src/corelib/io/qtemporaryfile.cpp b/src/corelib/io/qtemporaryfile.cpp
index 35bb465a04..ced08a9a87 100644
--- a/src/corelib/io/qtemporaryfile.cpp
+++ b/src/corelib/io/qtemporaryfile.cpp
@@ -908,8 +908,8 @@ QTemporaryFile *QTemporaryFile::createNativeFile(QFile &file)
         qint64 old_off = 0;
         if(wasOpen)
             old_off = file.pos();
-        else
-            file.open(QIODevice::ReadOnly);
+        else if (!file.open(QIODevice::ReadOnly))
+            return nullptr;
         //dump data
         QTemporaryFile *ret = new QTemporaryFile;
         if (ret->open()) {
diff --git a/src/corelib/kernel/qtranslator.cpp b/src/corelib/kernel/qtranslator.cpp
index dc39490ab0..a2111a084f 100644
--- a/src/corelib/kernel/qtranslator.cpp
+++ b/src/corelib/kernel/qtranslator.cpp
@@ -66,6 +66,7 @@
 #endif
 
 #include <stdlib.h>
+#include <new>
 
 #include "qobject_p.h"
 
@@ -585,7 +586,7 @@ bool QTranslatorPrivate::do_load(const QString &realname, const QString &directo
 #endif // QT_USE_MMAP
 
         if (!ok) {
-            d->unmapPointer = new char[d->unmapLength];
+            d->unmapPointer = new (std::nothrow) char[d->unmapLength];
             if (d->unmapPointer) {
                 file.seek(0);
                 qint64 readResult = file.read(d->unmapPointer, d->unmapLength);
diff --git a/src/gui/image/qimage.cpp b/src/gui/image/qimage.cpp
index 18e94cf256..0463ef6a42 100644
--- a/src/gui/image/qimage.cpp
+++ b/src/gui/image/qimage.cpp
@@ -124,7 +124,7 @@ QImageData * QImageData::create(const QSize &size, QImage::Format format)
     int height = size.height();
     int depth = qt_depthForFormat(format);
     auto params = calculateImageParameters(width, height, depth);
-    if (params.bytesPerLine < 0)
+    if (!params.isValid())
         return nullptr;
 
     QScopedPointer<QImageData> d(new QImageData);
@@ -783,7 +783,7 @@ QImageData *QImageData::create(uchar *data, int width, int height,  int bpl, QIm
 
     const int depth = qt_depthForFormat(format);
     auto params = calculateImageParameters(width, height, depth);
-    if (params.totalSize < 0)
+    if (!params.isValid())
         return nullptr;
 
     if (bpl > 0) {
@@ -1488,10 +1488,17 @@ qsizetype QImage::sizeInBytes() const
 
     \sa scanLine()
 */
+#if QT_VERSION >= QT_VERSION_CHECK(6,0,0)
+qsizetype QImage::bytesPerLine() const
+{
+    return d ? d->bytes_per_line : 0;
+}
+#else
 int QImage::bytesPerLine() const
 {
     return d ? d->bytes_per_line : 0;
 }
+#endif
 
 
 /*!
diff --git a/src/gui/image/qimage.h b/src/gui/image/qimage.h
index 45f571807c..8335e117f2 100644
--- a/src/gui/image/qimage.h
+++ b/src/gui/image/qimage.h
@@ -226,7 +226,11 @@ public:
     uchar *scanLine(int);
     const uchar *scanLine(int) const;
     const uchar *constScanLine(int) const;
+#if QT_VERSION >= QT_VERSION_CHECK(6,0,0)
+    qsizetype bytesPerLine() const;
+#else
     int bytesPerLine() const;
+#endif
 
     bool valid(int x, int y) const;
     bool valid(const QPoint &pt) const;
diff --git a/src/gui/image/qimage_p.h b/src/gui/image/qimage_p.h
index de12a313e8..d88ad2d1d2 100644
--- a/src/gui/image/qimage_p.h
+++ b/src/gui/image/qimage_p.h
@@ -109,6 +109,7 @@ struct Q_GUI_EXPORT QImageData {        // internal image data
     struct ImageSizeParameters {
         qsizetype bytesPerLine;
         qsizetype totalSize;
+        bool isValid() const { return bytesPerLine > 0 && totalSize > 0; }
     };
     static ImageSizeParameters calculateImageParameters(qsizetype width, qsizetype height, qsizetype depth);
 };
@@ -135,6 +136,11 @@ QImageData::calculateImageParameters(qsizetype width, qsizetype height, qsizetyp
     qsizetype dummy;
     if (mul_overflow(height, qsizetype(sizeof(uchar *)), &dummy))
         return invalid;                                 // why is this here?
+#if QT_VERSION < QT_VERSION_CHECK(6,0,0)
+    // Disallow images where width * depth calculations might overflow
+    if (width > (INT_MAX - 31) / depth)
+        return invalid;
+#endif
 
     return { bytes_per_line, total_size };
 }
diff --git a/src/gui/kernel/qplatformgraphicsbuffer.h b/src/gui/kernel/qplatformgraphicsbuffer.h
index 65c24bebc9..9004116ea4 100644
--- a/src/gui/kernel/qplatformgraphicsbuffer.h
+++ b/src/gui/kernel/qplatformgraphicsbuffer.h
@@ -71,12 +71,14 @@ public:
         TextureAccess       = 0x04,
         HWCompositor        = 0x08
     };
+    Q_ENUM(AccessType);
     Q_DECLARE_FLAGS(AccessTypes, AccessType);
 
     enum Origin {
         OriginBottomLeft,
         OriginTopLeft
     };
+    Q_ENUM(Origin);
 
     ~QPlatformGraphicsBuffer();
 
diff --git a/src/gui/kernel/qplatformintegration.cpp b/src/gui/kernel/qplatformintegration.cpp
index 199ef0de07..6ae6e4a528 100644
--- a/src/gui/kernel/qplatformintegration.cpp
+++ b/src/gui/kernel/qplatformintegration.cpp
@@ -463,40 +463,16 @@ QList<int> QPlatformIntegration::possibleKeys(const QKeyEvent *) const
 }
 
 /*!
-  Should be called by the implementation whenever a new screen is added.
-
-  The first screen added will be the primary screen, used for default-created
-  windows, GL contexts, and other resources unless otherwise specified.
-
-  This adds the screen to QGuiApplication::screens(), and emits the
-  QGuiApplication::screenAdded() signal.
-
-  The screen should be deleted by calling QPlatformIntegration::destroyScreen().
+  \deprecated Use QWindowSystemInterface::handleScreenAdded instead.
 */
 void QPlatformIntegration::screenAdded(QPlatformScreen *ps, bool isPrimary)
 {
-    QScreen *screen = new QScreen(ps);
-
-    if (isPrimary) {
-        QGuiApplicationPrivate::screen_list.prepend(screen);
-    } else {
-        QGuiApplicationPrivate::screen_list.append(screen);
-    }
-
-    QGuiApplicationPrivate::resetCachedDevicePixelRatio();
-
-    emit qGuiApp->screenAdded(screen);
-
-    if (isPrimary)
-        emit qGuiApp->primaryScreenChanged(screen);
+    QWindowSystemInterface::handleScreenAdded(ps, isPrimary);
 }
 
 /*!
-  Just removes the screen, call destroyScreen instead.
-
-  \sa destroyScreen()
+  \deprecated Use QWindowSystemInterface::handleScreenRemoved instead.
 */
-
 void QPlatformIntegration::removeScreen(QScreen *screen)
 {
     const bool wasPrimary = (!QGuiApplicationPrivate::screen_list.isEmpty() && QGuiApplicationPrivate::screen_list.at(0) == screen);
@@ -509,38 +485,19 @@ void QPlatformIntegration::removeScreen(QScreen *screen)
 }
 
 /*!
-  Should be called by the implementation whenever a screen is removed.
-
-  This removes the screen from QGuiApplication::screens(), and deletes it.
-
-  Failing to call this and manually deleting the QPlatformScreen instead may
-  lead to a crash due to a pure virtual call.
+  \deprecated Use QWindowSystemInterface::handleScreenRemoved instead.
 */
-void QPlatformIntegration::destroyScreen(QPlatformScreen *screen)
+void QPlatformIntegration::destroyScreen(QPlatformScreen *platformScreen)
 {
-    QScreen *qScreen = screen->screen();
-    removeScreen(qScreen);
-    delete qScreen;
-    delete screen;
+    QWindowSystemInterface::handleScreenRemoved(platformScreen);
 }
 
 /*!
-  Should be called whenever the primary screen changes.
-
-  When the screen specified as primary changes, this method will notify
-  QGuiApplication and emit the QGuiApplication::primaryScreenChanged signal.
- */
-
+  \deprecated Use QWindowSystemInterface::handlePrimaryScreenChanged instead.
+*/
 void QPlatformIntegration::setPrimaryScreen(QPlatformScreen *newPrimary)
 {
-    QScreen* newPrimaryScreen = newPrimary->screen();
-    int idx = QGuiApplicationPrivate::screen_list.indexOf(newPrimaryScreen);
-    Q_ASSERT(idx >= 0);
-    if (idx == 0)
-        return;
-
-    QGuiApplicationPrivate::screen_list.swapItemsAt(0, idx);
-    emit qGuiApp->primaryScreenChanged(newPrimaryScreen);
+    QWindowSystemInterface::handlePrimaryScreenChanged(newPrimary);
 }
 
 QStringList QPlatformIntegration::themeNames() const
diff --git a/src/gui/kernel/qplatformintegration.h b/src/gui/kernel/qplatformintegration.h
index de5f9c1c9a..6950bbaf72 100644
--- a/src/gui/kernel/qplatformintegration.h
+++ b/src/gui/kernel/qplatformintegration.h
@@ -192,7 +192,9 @@ public:
 #endif
     virtual void setApplicationIcon(const QIcon &icon) const;
 
-    void removeScreen(QScreen *screen);
+#if QT_DEPRECATED_SINCE(5, 12)
+    QT_DEPRECATED_X("Use QWindowSystemInterface::handleScreenRemoved") void removeScreen(QScreen *screen);
+#endif
 
     virtual void beep() const;
 
@@ -203,9 +205,11 @@ public:
 protected:
     QPlatformIntegration() = default;
 
-    void screenAdded(QPlatformScreen *screen, bool isPrimary = false);
-    void destroyScreen(QPlatformScreen *screen);
-    void setPrimaryScreen(QPlatformScreen *newPrimary);
+#if QT_DEPRECATED_SINCE(5, 12)
+    QT_DEPRECATED_X("Use QWindowSystemInterface::handleScreenAdded") void screenAdded(QPlatformScreen *screen, bool isPrimary = false);
+    QT_DEPRECATED_X("Use QWindowSystemInterface::handleScreenRemoved") void destroyScreen(QPlatformScreen *screen);
+    QT_DEPRECATED_X("Use QWindowSystemInterface::handlePrimaryScreenChanged") void setPrimaryScreen(QPlatformScreen *newPrimary);
+#endif
 };
 
 QT_END_NAMESPACE
diff --git a/src/gui/kernel/qplatformscreen.cpp b/src/gui/kernel/qplatformscreen.cpp
index b7b312e89e..21ae75ba8f 100644
--- a/src/gui/kernel/qplatformscreen.cpp
+++ b/src/gui/kernel/qplatformscreen.cpp
@@ -61,8 +61,11 @@ QPlatformScreen::~QPlatformScreen()
 {
     Q_D(QPlatformScreen);
     if (d->screen) {
-        qWarning("Manually deleting a QPlatformScreen. Call QPlatformIntegration::destroyScreen instead.");
+        qWarning("Manually deleting a QPlatformScreen. Call QWindowSystemInterface::handleScreenRemoved instead.");
+QT_WARNING_PUSH
+QT_WARNING_DISABLE_DEPRECATED
         QGuiApplicationPrivate::platformIntegration()->removeScreen(d->screen);
+QT_WARNING_POP
         delete d->screen;
     }
 }
diff --git a/src/gui/kernel/qscreen.h b/src/gui/kernel/qscreen.h
index 8c9b16e08e..14392d3036 100644
--- a/src/gui/kernel/qscreen.h
+++ b/src/gui/kernel/qscreen.h
@@ -169,6 +169,7 @@ private:
     friend class QPlatformIntegration;
     friend class QPlatformScreen;
     friend class QHighDpiScaling;
+    friend class QWindowSystemInterface;
 };
 
 #ifndef QT_NO_DEBUG_STREAM
diff --git a/src/gui/kernel/qwindow.cpp b/src/gui/kernel/qwindow.cpp
index 1cc2435239..590e2a85bb 100644
--- a/src/gui/kernel/qwindow.cpp
+++ b/src/gui/kernel/qwindow.cpp
@@ -1922,9 +1922,6 @@ void QWindowPrivate::destroy()
     resizeEventPending = true;
     receivedExpose = false;
     exposed = false;
-
-    if (wasVisible)
-        maybeQuitOnLastWindowClosed();
 }
 
 /*!
@@ -2313,8 +2310,17 @@ bool QWindow::event(QEvent *ev)
 #endif
 
     case QEvent::Close:
-        if (ev->isAccepted())
+        if (ev->isAccepted()) {
+            Q_D(QWindow);
+            bool wasVisible = isVisible();
             destroy();
+            if (wasVisible) {
+                // FIXME: This check for visibility is a workaround for both QWidgetWindow
+                // and QWindow having logic to emit lastWindowClosed, and possibly quit the
+                // application. We should find a better way to handle this.
+                d->maybeQuitOnLastWindowClosed();
+            }
+        }
         break;
 
     case QEvent::Expose:
diff --git a/src/gui/kernel/qwindowsysteminterface.cpp b/src/gui/kernel/qwindowsysteminterface.cpp
index 7067ece1d8..ec6911b334 100644
--- a/src/gui/kernel/qwindowsysteminterface.cpp
+++ b/src/gui/kernel/qwindowsysteminterface.cpp
@@ -780,6 +780,72 @@ QT_DEFINE_QPA_EVENT_HANDLER(void, handleTouchCancelEvent, QWindow *window, ulong
     QWindowSystemInterfacePrivate::handleWindowSystemEvent<Delivery>(e);
 }
 
+/*!
+    Should be called by the implementation whenever a new screen is added.
+
+    The first screen added will be the primary screen, used for default-created
+    windows, GL contexts, and other resources unless otherwise specified.
+
+    This adds the screen to QGuiApplication::screens(), and emits the
+    QGuiApplication::screenAdded() signal.
+
+    The screen should be deleted by calling QWindowSystemInterface::handleScreenRemoved().
+*/
+void QWindowSystemInterface::handleScreenAdded(QPlatformScreen *ps, bool isPrimary)
+{
+    QScreen *screen = new QScreen(ps);
+
+    if (isPrimary)
+        QGuiApplicationPrivate::screen_list.prepend(screen);
+    else
+        QGuiApplicationPrivate::screen_list.append(screen);
+
+    QGuiApplicationPrivate::resetCachedDevicePixelRatio();
+
+    emit qGuiApp->screenAdded(screen);
+
+    if (isPrimary)
+        emit qGuiApp->primaryScreenChanged(screen);
+}
+
+/*!
+    Should be called by the implementation whenever a screen is removed.
+
+    This removes the screen from QGuiApplication::screens(), and deletes it.
+
+    Failing to call this and manually deleting the QPlatformScreen instead may
+    lead to a crash due to a pure virtual call.
+*/
+void QWindowSystemInterface::handleScreenRemoved(QPlatformScreen *platformScreen)
+{
+QT_WARNING_PUSH
+QT_WARNING_DISABLE_DEPRECATED
+    QGuiApplicationPrivate::platformIntegration()->removeScreen(platformScreen->screen());
+QT_WARNING_POP
+
+    // Important to keep this order since the QSceen doesn't own the platform screen
+    delete platformScreen->screen();
+    delete platformScreen;
+}
+
+/*!
+    Should be called whenever the primary screen changes.
+
+    When the screen specified as primary changes, this method will notify
+    QGuiApplication and emit the QGuiApplication::primaryScreenChanged signal.
+ */
+void QWindowSystemInterface::handlePrimaryScreenChanged(QPlatformScreen *newPrimary)
+{
+    QScreen *newPrimaryScreen = newPrimary->screen();
+    int indexOfScreen = QGuiApplicationPrivate::screen_list.indexOf(newPrimaryScreen);
+    Q_ASSERT(indexOfScreen >= 0);
+    if (indexOfScreen == 0)
+        return;
+
+    QGuiApplicationPrivate::screen_list.swapItemsAt(0, indexOfScreen);
+    emit qGuiApp->primaryScreenChanged(newPrimaryScreen);
+}
+
 void QWindowSystemInterface::handleScreenOrientationChange(QScreen *screen, Qt::ScreenOrientation orientation)
 {
     QWindowSystemInterfacePrivate::ScreenOrientationEvent *e =
diff --git a/src/gui/kernel/qwindowsysteminterface.h b/src/gui/kernel/qwindowsysteminterface.h
index 1dde9130ac..bf98c33a1a 100644
--- a/src/gui/kernel/qwindowsysteminterface.h
+++ b/src/gui/kernel/qwindowsysteminterface.h
@@ -233,6 +233,10 @@ public:
     static bool handleNativeEvent(QWindow *window, const QByteArray &eventType, void *message, long *result);
 
     // Changes to the screen
+    static void handleScreenAdded(QPlatformScreen *screen, bool isPrimary = false);
+    static void handleScreenRemoved(QPlatformScreen *screen);
+    static void handlePrimaryScreenChanged(QPlatformScreen *newPrimary);
+
     static void handleScreenOrientationChange(QScreen *screen, Qt::ScreenOrientation newOrientation);
     static void handleScreenGeometryChange(QScreen *screen, const QRect &newGeometry, const QRect &newAvailableGeometry);
     static void handleScreenLogicalDotsPerInchChange(QScreen *screen, qreal newDpiX, qreal newDpiY);
diff --git a/src/gui/text/qtextdocumentlayout.cpp b/src/gui/text/qtextdocumentlayout.cpp
index 323253c70d..2e1a2b5bff 100644
--- a/src/gui/text/qtextdocumentlayout.cpp
+++ b/src/gui/text/qtextdocumentlayout.cpp
@@ -58,23 +58,17 @@
 #include <limits.h>
 #include <qbasictimer.h>
 #include "private/qfunctions_p.h"
+#include <qloggingcategory.h>
 
 #include <algorithm>
 
-// #define LAYOUT_DEBUG
-
-#ifdef LAYOUT_DEBUG
-#define LDEBUG qDebug()
-#define INC_INDENT debug_indent += "  "
-#define DEC_INDENT debug_indent = debug_indent.left(debug_indent.length()-2)
-#else
-#define LDEBUG if(0) qDebug()
-#define INC_INDENT do {} while(0)
-#define DEC_INDENT do {} while(0)
-#endif
-
 QT_BEGIN_NAMESPACE
 
+Q_LOGGING_CATEGORY(lcDraw, "qt.text.drawing")
+Q_LOGGING_CATEGORY(lcHit, "qt.text.hittest")
+Q_LOGGING_CATEGORY(lcLayout, "qt.text.layout")
+Q_LOGGING_CATEGORY(lcTable, "qt.text.layout.table")
+
 // ################ should probably add frameFormatChange notification!
 
 struct QTextLayoutStruct;
@@ -583,16 +577,16 @@ QTextDocumentLayoutPrivate::hitTest(QTextFrame *frame, const QFixedPoint &point,
 
     QTextFrame *rootFrame = docPrivate->rootFrame();
 
-//     LDEBUG << "checking frame" << frame->firstPosition() << "point=" << point
-//            << "position" << fd->position << "size" << fd->size;
+    qCDebug(lcHit) << "checking frame" << frame->firstPosition() << "point=" << point.toPointF()
+                   << "position" << fd->position.toPointF() << "size" << fd->size.toSizeF();
     if (frame != rootFrame) {
         if (relativePoint.y < 0 || relativePoint.x < 0) {
             *position = frame->firstPosition() - 1;
-//             LDEBUG << "before pos=" << *position;
+            qCDebug(lcHit) << "before pos=" << *position;
             return PointBefore;
         } else if (relativePoint.y > fd->size.height || relativePoint.x > fd->size.width) {
             *position = frame->lastPosition() + 1;
-//             LDEBUG << "after pos=" << *position;
+            qCDebug(lcHit) << "after pos=" << *position;
             return PointAfter;
         }
     }
@@ -666,8 +660,6 @@ QTextDocumentLayoutPrivate::HitPoint
 QTextDocumentLayoutPrivate::hitTest(QTextFrame::Iterator it, HitPoint hit, const QFixedPoint &p,
                                     int *position, QTextLayout **l, Qt::HitTestAccuracy accuracy) const
 {
-    INC_INDENT;
-
     for (; !it.atEnd(); ++it) {
         QTextFrame *c = it.currentFrame();
         HitPoint hp;
@@ -693,8 +685,7 @@ QTextDocumentLayoutPrivate::hitTest(QTextFrame::Iterator it, HitPoint hit, const
         }
     }
 
-    DEC_INDENT;
-//     LDEBUG << "inside=" << hit << " pos=" << *position;
+    qCDebug(lcHit) << "inside=" << hit << " pos=" << *position;
     return hit;
 }
 
@@ -741,15 +732,14 @@ QTextDocumentLayoutPrivate::hitTest(const QTextBlock &bl, const QFixedPoint &poi
     QTextLayout *tl = bl.layout();
     QRectF textrect = tl->boundingRect();
     textrect.translate(tl->position());
-//     LDEBUG << "    checking block" << bl.position() << "point=" << point
-//            << "    tlrect" << textrect;
+    qCDebug(lcHit) << "    checking block" << bl.position() << "point=" << point.toPointF() << "    tlrect" << textrect;
     *position = bl.position();
     if (point.y.toReal() < textrect.top()) {
-//             LDEBUG << "    before pos=" << *position;
+        qCDebug(lcHit) << "    before pos=" << *position;
         return PointBefore;
     } else if (point.y.toReal() > textrect.bottom()) {
         *position += bl.length();
-//             LDEBUG << "    after pos=" << *position;
+        qCDebug(lcHit) << "    after pos=" << *position;
         return PointAfter;
     }
 
@@ -781,7 +771,7 @@ QTextDocumentLayoutPrivate::hitTest(const QTextBlock &bl, const QFixedPoint &poi
     }
     *position += off;
 
-//     LDEBUG << "    inside=" << hit << " pos=" << *position;
+    qCDebug(lcHit) << "    inside=" << hit << " pos=" << *position;
     return hit;
 }
 
@@ -944,8 +934,7 @@ void QTextDocumentLayoutPrivate::drawFrame(const QPointF &offset, QPainter *pain
             || off.x() > context.clip.right() || off.x() + fd->size.width.toReal() < context.clip.left()))
         return;
 
-//     LDEBUG << debug_indent << "drawFrame" << frame->firstPosition() << "--" << frame->lastPosition() << "at" << offset;
-//     INC_INDENT;
+     qCDebug(lcDraw) << "drawFrame" << frame->firstPosition() << "--" << frame->lastPosition() << "at" << offset;
 
     // if the cursor is /on/ a table border we may need to repaint it
     // afterwards, as we usually draw the decoration first
@@ -1076,8 +1065,6 @@ void QTextDocumentLayoutPrivate::drawFrame(const QPointF &offset, QPainter *pain
         painter->setPen(oldPen);
     }
 
-//     DEC_INDENT;
-
     return;
 }
 
@@ -1280,7 +1267,7 @@ void QTextDocumentLayoutPrivate::drawBlock(const QPointF &offset, QPainter *pain
     r.translate(offset + tl->position());
     if (!bl.isVisible() || (context.clip.isValid() && (r.bottom() < context.clip.y() || r.top() > context.clip.bottom())))
         return;
-//      LDEBUG << debug_indent << "drawBlock" << bl.position() << "at" << offset << "br" << tl->boundingRect();
+    qCDebug(lcDraw) << "drawBlock" << bl.position() << "at" << offset << "br" << tl->boundingRect();
 
     QTextBlockFormat blockFormat = bl.blockFormat();
 
@@ -1512,7 +1499,7 @@ QTextLayoutStruct QTextDocumentLayoutPrivate::layoutCell(QTextTable *t, const QT
                                                         int layoutFrom, int layoutTo, QTextTableData *td,
                                                         QFixed absoluteTableY, bool withPageBreaks)
 {
-    LDEBUG << "layoutCell";
+    qCDebug(lcTable) << "layoutCell";
     QTextLayoutStruct layoutStruct;
     layoutStruct.frame = t;
     layoutStruct.minimumWidth = 0;
@@ -1587,7 +1574,7 @@ QTextLayoutStruct QTextDocumentLayoutPrivate::layoutCell(QTextTable *t, const QT
 
 QRectF QTextDocumentLayoutPrivate::layoutTable(QTextTable *table, int layoutFrom, int layoutTo, QFixed parentY)
 {
-    LDEBUG << "layoutTable";
+    qCDebug(lcTable) << "layoutTable from" << layoutFrom << "to" << layoutTo << "parentY" << parentY;
     QTextTableData *td = static_cast<QTextTableData *>(data(table));
     Q_ASSERT(td->sizeDirty);
     const int rows = table->rows();
@@ -1709,6 +1696,7 @@ recalc_minmax_widths:
         if (length.type() == QTextLength::FixedLength) {
             td->minWidths[i] = td->widths[i] = qMax(scaleToDevice(QFixed::fromReal(length.rawValue())), td->minWidths.at(i));
             remainingWidth -= td->widths.at(i);
+            qCDebug(lcTable) << "column" << i << "has width constraint" << td->minWidths.at(i) << "px, remaining width now" << remainingWidth;
         } else if (length.type() == QTextLength::PercentageLength) {
             totalPercentage += QFixed::fromReal(length.rawValue());
         } else if (length.type() == QTextLength::VariableLength) {
@@ -1716,6 +1704,7 @@ recalc_minmax_widths:
 
             td->widths[i] = td->minWidths.at(i);
             remainingWidth -= td->minWidths.at(i);
+            qCDebug(lcTable) << "column" << i << "has variable width, min" << td->minWidths.at(i) << "remaining width now" << remainingWidth;
         }
         totalMinWidth += td->minWidths.at(i);
     }
@@ -1735,6 +1724,8 @@ recalc_minmax_widths:
                 } else {
                     td->widths[i] = td->minWidths.at(i);
                 }
+                qCDebug(lcTable) << "column" << i << "has width constraint" << columnWidthConstraints.at(i).rawValue()
+                                 << "%, allocated width" << td->widths[i] << "remaining width now" << remainingWidth;
                 remainingWidth -= td->widths.at(i);
             }
         }
@@ -1978,9 +1969,12 @@ relayout:
     td->minimumWidth += rightMargin - td->border;
 
     td->maximumWidth = td->columnPositions.at(0);
-    for (int i = 0; i < columns; ++i)
+    for (int i = 0; i < columns; ++i) {
         if (td->maxWidths.at(i) != QFIXED_MAX)
             td->maximumWidth += td->maxWidths.at(i) + 2 * td->border + cellSpacing;
+        qCDebug(lcTable) << "column" << i << "has final width" << td->widths.at(i).toReal()
+                         << "min" << td->minWidths.at(i).toReal() << "max" << td->maxWidths.at(i).toReal();
+    }
     td->maximumWidth += rightMargin - td->border;
 
     td->updateTableSize();
@@ -2052,9 +2046,8 @@ void QTextDocumentLayoutPrivate::positionFloat(QTextFrame *frame, QTextLine *cur
 
 QRectF QTextDocumentLayoutPrivate::layoutFrame(QTextFrame *f, int layoutFrom, int layoutTo, QFixed parentY)
 {
-    LDEBUG << "layoutFrame (pre)";
+    qCDebug(lcLayout, "layoutFrame (%d--%d), parent=%p", f->firstPosition(), f->lastPosition(), f->parentFrame());
     Q_ASSERT(data(f)->sizeDirty);
-//     qDebug("layouting frame (%d--%d), parent=%p", f->firstPosition(), f->lastPosition(), f->parentFrame());
 
     QTextFrameFormat fformat = f->frameFormat();
 
@@ -2076,9 +2069,8 @@ QRectF QTextDocumentLayoutPrivate::layoutFrame(QTextFrame *f, int layoutFrom, in
 
 QRectF QTextDocumentLayoutPrivate::layoutFrame(QTextFrame *f, int layoutFrom, int layoutTo, QFixed frameWidth, QFixed frameHeight, QFixed parentY)
 {
-    LDEBUG << "layoutFrame from=" << layoutFrom << "to=" << layoutTo;
+    qCDebug(lcLayout, "layoutFrame (%d--%d), parent=%p", f->firstPosition(), f->lastPosition(), f->parentFrame());
     Q_ASSERT(data(f)->sizeDirty);
-//     qDebug("layouting frame (%d--%d), parent=%p", f->firstPosition(), f->lastPosition(), f->parentFrame());
 
     QTextFrameData *fd = data(f);
     QFixed newContentsWidth;
@@ -2165,8 +2157,8 @@ QRectF QTextDocumentLayoutPrivate::layoutFrame(QTextFrame *f, int layoutFrom, in
     layoutStruct.maximumWidth = QFIXED_MAX;
     layoutStruct.fullLayout = fullLayout || (fd->oldContentsWidth != newContentsWidth);
     layoutStruct.updateRect = QRectF(QPointF(0, 0), QSizeF(qreal(INT_MAX), qreal(INT_MAX)));
-    LDEBUG << "layoutStruct: x_left" << layoutStruct.x_left << "x_right" << layoutStruct.x_right
-           << "fullLayout" << layoutStruct.fullLayout;
+    qCDebug(lcLayout) << "layoutStruct: x_left" << layoutStruct.x_left << "x_right" << layoutStruct.x_right
+                      << "fullLayout" << layoutStruct.fullLayout;
     fd->oldContentsWidth = newContentsWidth;
 
     layoutStruct.pageHeight = QFixed::fromReal(document->pageSize().height());
@@ -2220,7 +2212,7 @@ QRectF QTextDocumentLayoutPrivate::layoutFrame(QTextFrame *f, int layoutFrom, in
 void QTextDocumentLayoutPrivate::layoutFlow(QTextFrame::Iterator it, QTextLayoutStruct *layoutStruct,
                                             int layoutFrom, int layoutTo, QFixed width)
 {
-    LDEBUG << "layoutFlow from=" << layoutFrom << "to=" << layoutTo;
+    qCDebug(lcLayout) << "layoutFlow from=" << layoutFrom << "to=" << layoutTo;
     QTextFrameData *fd = data(layoutStruct->frame);
 
     fd->currentLayoutStruct = layoutStruct;
@@ -2578,9 +2570,8 @@ void QTextDocumentLayoutPrivate::layoutBlock(const QTextBlock &bl, int blockPosi
     QTextLayout *tl = bl.layout();
     const int blockLength = bl.length();
 
-    LDEBUG << "layoutBlock from=" << layoutFrom << "to=" << layoutTo;
-
-//    qDebug() << "layoutBlock; width" << layoutStruct->x_right - layoutStruct->x_left << "(maxWidth is btw" << tl->maximumWidth() << ')';
+    qCDebug(lcLayout) << "layoutBlock from=" << layoutFrom << "to=" << layoutTo
+                      << "; width" << layoutStruct->x_right - layoutStruct->x_left << "(maxWidth is btw" << tl->maximumWidth() << ')';
 
     if (previousBlockFormat) {
         qreal margin = qMax(blockFormat.topMargin(), previousBlockFormat->bottomMargin());
@@ -2612,7 +2603,7 @@ void QTextDocumentLayoutPrivate::layoutBlock(const QTextBlock &bl, int blockPosi
         // force relayout if we cross a page boundary
         || (layoutStruct->pageHeight != QFIXED_MAX && layoutStruct->absoluteY() + QFixed::fromReal(tl->boundingRect().height()) > layoutStruct->pageBottom)) {
 
-        LDEBUG << " do layout";
+        qCDebug(lcLayout) << "do layout";
         QTextOption option = docPrivate->defaultTextOption;
         option.setTextDirection(dir);
         option.setTabs( blockFormat.tabPositions() );
@@ -2741,7 +2732,7 @@ void QTextDocumentLayoutPrivate::layoutBlock(const QTextBlock &bl, int blockPosi
         const int cnt = tl->lineCount();
         QFixed bottom;
         for (int i = 0; i < cnt; ++i) {
-            LDEBUG << "going to move text line" << i;
+            qCDebug(lcLayout) << "going to move text line" << i;
             QTextLine line = tl->lineAt(i);
             layoutStruct->contentsWidth
                 = qMax(layoutStruct->contentsWidth, QFixed::fromReal(line.x() + tl->lineAt(i).naturalTextWidth()) + totalRightMargin);
diff --git a/src/network/configure.json b/src/network/configure.json
index e6c87b550b..07d46b790e 100644
--- a/src/network/configure.json
+++ b/src/network/configure.json
@@ -86,11 +86,11 @@
             "sources": [
                 { "type": "openssl" },
                 {
-                    "libs": "-lssleay32 -llibeay32",
+                    "libs": "-lssleay32 -llibeay32 -lUser32 -lWs2_32 -lAdvapi32 -lGdi32",
                     "condition": "config.win32"
                 },
                 {
-                    "libs": "-llibssl -llibcrypto",
+                    "libs": "-llibssl -llibcrypto -lUser32 -lWs2_32 -lAdvapi32 -lCrypt32",
                     "condition": "config.msvc"
                 },
                 {
diff --git a/src/plugins/platforms/android/qandroidplatformintegration.cpp b/src/plugins/platforms/android/qandroidplatformintegration.cpp
index 763b294660..e0c437be27 100644
--- a/src/plugins/platforms/android/qandroidplatformintegration.cpp
+++ b/src/plugins/platforms/android/qandroidplatformintegration.cpp
@@ -173,7 +173,7 @@ QAndroidPlatformIntegration::QAndroidPlatformIntegration(const QStringList &para
         qFatal("Could not bind GL_ES API");
 
     m_primaryScreen = new QAndroidPlatformScreen();
-    screenAdded(m_primaryScreen);
+    QWindowSystemInterface::handleScreenAdded(m_primaryScreen);
     m_primaryScreen->setPhysicalSize(QSize(m_defaultPhysicalSizeWidth, m_defaultPhysicalSizeHeight));
     m_primaryScreen->setSize(QSize(m_defaultScreenWidth, m_defaultScreenHeight));
     m_primaryScreen->setAvailableGeometry(QRect(0, 0, m_defaultGeometryWidth, m_defaultGeometryHeight));
diff --git a/src/plugins/platforms/bsdfb/qbsdfbintegration.cpp b/src/plugins/platforms/bsdfb/qbsdfbintegration.cpp
index 6a7d445e69..e4c90d26af 100644
--- a/src/plugins/platforms/bsdfb/qbsdfbintegration.cpp
+++ b/src/plugins/platforms/bsdfb/qbsdfbintegration.cpp
@@ -53,6 +53,7 @@
 #include <QtGui/private/qguiapplication_p.h>
 #include <qpa/qplatforminputcontext.h>
 #include <qpa/qplatforminputcontextfactory_p.h>
+#include <qpa/qwindowsysteminterface.h>
 
 #if QT_CONFIG(tslib)
 #include <QtInputSupport/private/qtslib_p.h>
@@ -69,13 +70,13 @@ QBsdFbIntegration::QBsdFbIntegration(const QStringList &paramList)
 
 QBsdFbIntegration::~QBsdFbIntegration()
 {
-    destroyScreen(m_primaryScreen.take());
+    QWindowSystemInterface::handleScreenRemoved(m_primaryScreen.take());
 }
 
 void QBsdFbIntegration::initialize()
 {
     if (m_primaryScreen->initialize())
-        screenAdded(m_primaryScreen.data());
+        QWindowSystemInterface::handleScreenAdded(m_primaryScreen.data());
     else
         qWarning("bsdfb: Failed to initialize screen");
 
diff --git a/src/plugins/platforms/cocoa/cocoa.pro b/src/plugins/platforms/cocoa/cocoa.pro
index 8d65cf328f..083b7c1655 100644
--- a/src/plugins/platforms/cocoa/cocoa.pro
+++ b/src/plugins/platforms/cocoa/cocoa.pro
@@ -33,6 +33,7 @@ SOURCES += main.mm \
     qcocoaintrospection.mm \
     qcocoakeymapper.mm \
     qcocoamimetypes.mm \
+    qiosurfacegraphicsbuffer.mm \
     messages.cpp
 
 HEADERS += qcocoaintegration.h \
@@ -67,6 +68,7 @@ HEADERS += qcocoaintegration.h \
     qcocoaintrospection.h \
     qcocoakeymapper.h \
     messages.h \
+    qiosurfacegraphicsbuffer.h \
     qcocoamimetypes.h
 
 qtConfig(opengl.*) {
@@ -81,7 +83,7 @@ qtConfig(vulkan) {
 
 RESOURCES += qcocoaresources.qrc
 
-LIBS += -framework AppKit -framework CoreServices -framework Carbon -framework IOKit -framework QuartzCore -framework CoreVideo -framework Metal -lcups
+LIBS += -framework AppKit -framework CoreServices -framework Carbon -framework IOKit -framework QuartzCore -framework CoreVideo -framework Metal -framework IOSurface -lcups
 
 QT += \
     core-private gui-private \
diff --git a/src/plugins/platforms/cocoa/qcocoabackingstore.h b/src/plugins/platforms/cocoa/qcocoabackingstore.h
index b4cd506513..508f24d578 100644
--- a/src/plugins/platforms/cocoa/qcocoabackingstore.h
+++ b/src/plugins/platforms/cocoa/qcocoabackingstore.h
@@ -44,13 +44,16 @@
 
 #include <private/qcore_mac_p.h>
 
+#include <QScopedPointer>
+#include "qiosurfacegraphicsbuffer.h"
+
 QT_BEGIN_NAMESPACE
 
-class QCocoaBackingStore : public QRasterBackingStore
+class QNSWindowBackingStore : public QRasterBackingStore
 {
 public:
-    QCocoaBackingStore(QWindow *window);
-    ~QCocoaBackingStore();
+    QNSWindowBackingStore(QWindow *window);
+    ~QNSWindowBackingStore();
 
     void flush(QWindow *, const QRegion &, const QPoint &) override;
 
@@ -60,6 +63,49 @@ private:
     void redrawRoundedBottomCorners(CGRect) const;
 };
 
+class QCALayerBackingStore : public QPlatformBackingStore
+{
+public:
+    QCALayerBackingStore(QWindow *window);
+    ~QCALayerBackingStore();
+
+    void resize(const QSize &size, const QRegion &staticContents) override;
+
+    void beginPaint(const QRegion &region) override;
+    QPaintDevice *paintDevice() override;
+    void endPaint() override;
+
+    void flush(QWindow *, const QRegion &, const QPoint &) override;
+    void composeAndFlush(QWindow *window, const QRegion &region, const QPoint &offset,
+        QPlatformTextureList *textures, bool translucentBackground) override;
+
+    QPlatformGraphicsBuffer *graphicsBuffer() const override;
+
+private:
+    QSize m_requestedSize;
+    QRegion m_paintedRegion;
+
+    class GraphicsBuffer : public QIOSurfaceGraphicsBuffer
+    {
+    public:
+        GraphicsBuffer(const QSize &size, qreal devicePixelRatio,
+                const QPixelFormat &format, QCFType<CGColorSpaceRef> colorSpace);
+
+        QRegion dirtyRegion; // In unscaled coordinates
+        QImage *asImage();
+
+    private:
+        qreal m_devicePixelRatio;
+        QImage m_image;
+    };
+
+    void ensureBackBuffer();
+    bool recreateBackBufferIfNeeded();
+    bool prepareForFlush();
+
+    std::list<std::unique_ptr<GraphicsBuffer>> m_buffers;
+};
+
 QT_END_NAMESPACE
 
 #endif
diff --git a/src/plugins/platforms/cocoa/qcocoabackingstore.mm b/src/plugins/platforms/cocoa/qcocoabackingstore.mm
index 81a0a7d040..8e4e928bc5 100644
--- a/src/plugins/platforms/cocoa/qcocoabackingstore.mm
+++ b/src/plugins/platforms/cocoa/qcocoabackingstore.mm
@@ -42,24 +42,28 @@
 #include "qcocoawindow.h"
 #include "qcocoahelpers.h"
 
+#include <QtCore/qmath.h>
+
+#include <QuartzCore/CATransaction.h>
+
 QT_BEGIN_NAMESPACE
 
-QCocoaBackingStore::QCocoaBackingStore(QWindow *window)
+QNSWindowBackingStore::QNSWindowBackingStore(QWindow *window)
     : QRasterBackingStore(window)
 {
 }
 
-QCocoaBackingStore::~QCocoaBackingStore()
+QNSWindowBackingStore::~QNSWindowBackingStore()
 {
 }
 
-bool QCocoaBackingStore::windowHasUnifiedToolbar() const
+bool QNSWindowBackingStore::windowHasUnifiedToolbar() const
 {
     Q_ASSERT(window()->handle());
     return static_cast<QCocoaWindow *>(window()->handle())->m_drawContentBorderGradient;
 }
 
-QImage::Format QCocoaBackingStore::format() const
+QImage::Format QNSWindowBackingStore::format() const
 {
     if (windowHasUnifiedToolbar())
         return QImage::Format_ARGB32_Premultiplied;
@@ -78,7 +82,7 @@ QImage::Format QCocoaBackingStore::format() const
     coordinates, and the \a offset will be the child window's offset in relation
     to the backingstore's top level window.
 */
-void QCocoaBackingStore::flush(QWindow *window, const QRegion &region, const QPoint &offset)
+void QNSWindowBackingStore::flush(QWindow *window, const QRegion &region, const QPoint &offset)
 {
     if (m_image.isNull())
         return;
@@ -103,131 +107,113 @@ void QCocoaBackingStore::flush(QWindow *window, const QRegion &region, const QPo
         qCDebug(lcQpaBackingStore) << "Flushing" << region << "of" << view << qPrintable(targetViewDescription);
     }
 
-    // Prevent potentially costly color conversion by assigning the display color space
-    // to the backingstore image. This does not copy the underlying image data.
-    CGColorSpaceRef displayColorSpace = view.window.screen.colorSpace.CGColorSpace;
-    QCFType<CGImageRef> cgImage = CGImageCreateCopyWithColorSpace(
-        QCFType<CGImageRef>(m_image.toCGImage()), displayColorSpace);
-
-    if (view.layer) {
-        // In layer-backed mode, locking focus on a view does not give the right
-        // view transformation, and doesn't give us a graphics context to render
-        // via when drawing outside of the display cycle. Instead we tell AppKit
-        // that we want to update the layer's content, via [NSView wantsUpdateLayer],
-        // which result in AppKit not creating a backingstore for each layer, and
-        // we then directly set the layer's backingstore (content) to our backingstore,
-        // masked to the part of the subview that is relevant.
-        // FIXME: Figure out if there's a way to do partial updates
-        view.layer.contents = (__bridge id)static_cast<CGImageRef>(cgImage);
-        if (view != topLevelView) {
-            const CGSize topLevelSize = topLevelView.bounds.size;
-            view.layer.contentsRect = CGRectApplyAffineTransform(
-                [view convertRect:view.bounds toView:topLevelView],
-                // The contentsRect is in unit coordinate system
-                CGAffineTransformMakeScale(1.0 / topLevelSize.width, 1.0 / topLevelSize.height));
-        }
-    } else {
-        // Normally a NSView is drawn via drawRect, as part of the display cycle in the
-        // main runloop, via setNeedsDisplay and friends. AppKit will lock focus on each
-        // individual view, starting with the top level and then traversing any subviews,
-        // calling drawRect for each of them. This pull model results in expose events
-        // sent to Qt, which result in drawing to the backingstore and flushing it.
-        // Qt may also decide to paint and flush the backingstore via e.g. timers,
-        // or other events such as mouse events, in which case we're in a push model.
-        // If there is no focused view, it means we're in the latter case, and need
-        // to manually flush the NSWindow after drawing to its graphic context.
-        const bool drawingOutsideOfDisplayCycle = ![NSView focusView];
-
-        // We also need to ensure the flushed view has focus, so that the graphics
-        // context is set up correctly (coordinate system, clipping, etc). Outside
-        // of the normal display cycle there is no focused view, as explained above,
-        // so we have to handle it manually. There's also a corner case inside the
-        // normal display cycle due to way QWidgetBackingStore composits native child
-        // widgets, where we'll get a flush of a native child during the drawRect of
-        // its parent/ancestor, and the parent/ancestor being the one locked by AppKit.
-        // In this case we also need to lock and unlock focus manually.
-        const bool shouldHandleViewLockManually = [NSView focusView] != view;
-        if (shouldHandleViewLockManually && ![view lockFocusIfCanDraw]) {
-            qWarning() << "failed to lock focus of" << view;
-            return;
-        }
+    // Normally a NSView is drawn via drawRect, as part of the display cycle in the
+    // main runloop, via setNeedsDisplay and friends. AppKit will lock focus on each
+    // individual view, starting with the top level and then traversing any subviews,
+    // calling drawRect for each of them. This pull model results in expose events
+    // sent to Qt, which result in drawing to the backingstore and flushing it.
+    // Qt may also decide to paint and flush the backingstore via e.g. timers,
+    // or other events such as mouse events, in which case we're in a push model.
+    // If there is no focused view, it means we're in the latter case, and need
+    // to manually flush the NSWindow after drawing to its graphic context.
+    const bool drawingOutsideOfDisplayCycle = ![NSView focusView];
+
+    // We also need to ensure the flushed view has focus, so that the graphics
+    // context is set up correctly (coordinate system, clipping, etc). Outside
+    // of the normal display cycle there is no focused view, as explained above,
+    // so we have to handle it manually. There's also a corner case inside the
+    // normal display cycle due to way QWidgetBackingStore composits native child
+    // widgets, where we'll get a flush of a native child during the drawRect of
+    // its parent/ancestor, and the parent/ancestor being the one locked by AppKit.
+    // In this case we also need to lock and unlock focus manually.
+    const bool shouldHandleViewLockManually = [NSView focusView] != view;
+    if (shouldHandleViewLockManually && ![view lockFocusIfCanDraw]) {
+        qWarning() << "failed to lock focus of" << view;
+        return;
+    }
 
-        const qreal devicePixelRatio = m_image.devicePixelRatio();
+    const qreal devicePixelRatio = m_image.devicePixelRatio();
 
-        // If the flushed window is a content view, and we're filling the drawn area
-        // completely, or it doesn't have a window background we need to preserve,
-        // we can get away with copying instead of blending the backing store.
-        QCocoaWindow *cocoaWindow = static_cast<QCocoaWindow *>(window->handle());
-        const NSCompositingOperation compositingOperation = cocoaWindow->isContentView()
-            && (cocoaWindow->isOpaque() || view.window.backgroundColor == NSColor.clearColor)
-                ? NSCompositingOperationCopy : NSCompositingOperationSourceOver;
+    // If the flushed window is a content view, and we're filling the drawn area
+    // completely, or it doesn't have a window background we need to preserve,
+    // we can get away with copying instead of blending the backing store.
+    QCocoaWindow *cocoaWindow = static_cast<QCocoaWindow *>(window->handle());
+    const NSCompositingOperation compositingOperation = cocoaWindow->isContentView()
+        && (cocoaWindow->isOpaque() || view.window.backgroundColor == NSColor.clearColor)
+            ? NSCompositingOperationCopy : NSCompositingOperationSourceOver;
 
 #ifdef QT_DEBUG
-        static bool debugBackingStoreFlush = [[NSUserDefaults standardUserDefaults]
-            boolForKey:@"QtCocoaDebugBackingStoreFlush"];
+    static bool debugBackingStoreFlush = [[NSUserDefaults standardUserDefaults]
+        boolForKey:@"QtCocoaDebugBackingStoreFlush"];
 #endif
 
-        // -------------------------------------------------------------------------
+    // -------------------------------------------------------------------------
 
-        // The current contexts is typically a NSWindowGraphicsContext, but can be
-        // NSBitmapGraphicsContext e.g. when debugging the view hierarchy in Xcode.
-        // If we need to distinguish things here in the future, we can use e.g.
-        // [NSGraphicsContext drawingToScreen], or the attributes of the context.
-        NSGraphicsContext *graphicsContext = [NSGraphicsContext currentContext];
-        Q_ASSERT_X(graphicsContext, "QCocoaBackingStore",
-            "Focusing the view should give us a current graphics context");
+    // The current contexts is typically a NSWindowGraphicsContext, but can be
+    // NSBitmapGraphicsContext e.g. when debugging the view hierarchy in Xcode.
+    // If we need to distinguish things here in the future, we can use e.g.
+    // [NSGraphicsContext drawingToScreen], or the attributes of the context.
+    NSGraphicsContext *graphicsContext = [NSGraphicsContext currentContext];
+    Q_ASSERT_X(graphicsContext, "QCocoaBackingStore",
+        "Focusing the view should give us a current graphics context");
 
-        // Create temporary image to use for blitting, without copying image data
-        NSImage *backingStoreImage = [[[NSImage alloc] initWithCGImage:cgImage size:NSZeroSize] autorelease];
+    // Prevent potentially costly color conversion by assigning the display color space
+    // to the backingstore image. This does not copy the underlying image data.
+    CGColorSpaceRef displayColorSpace = view.window.screen.colorSpace.CGColorSpace;
+    QCFType<CGImageRef> cgImage = CGImageCreateCopyWithColorSpace(
+        QCFType<CGImageRef>(m_image.toCGImage()), displayColorSpace);
 
-        QRegion clippedRegion = region;
-        for (QWindow *w = window; w; w = w->parent()) {
-            if (!w->mask().isEmpty()) {
-                clippedRegion &= w == window ? w->mask()
-                    : w->mask().translated(window->mapFromGlobal(w->mapToGlobal(QPoint(0, 0))));
-            }
+    // Create temporary image to use for blitting, without copying image data
+    NSImage *backingStoreImage = [[[NSImage alloc] initWithCGImage:cgImage size:NSZeroSize] autorelease];
+
+    QRegion clippedRegion = region;
+    for (QWindow *w = window; w; w = w->parent()) {
+        if (!w->mask().isEmpty()) {
+            clippedRegion &= w == window ? w->mask()
+                : w->mask().translated(window->mapFromGlobal(w->mapToGlobal(QPoint(0, 0))));
         }
+    }
 
-        for (const QRect &viewLocalRect : clippedRegion) {
-            QPoint backingStoreOffset = viewLocalRect.topLeft() + offset;
-            QRect backingStoreRect(backingStoreOffset * devicePixelRatio, viewLocalRect.size() * devicePixelRatio);
-            if (graphicsContext.flipped) // Flip backingStoreRect to match graphics context
-                backingStoreRect.moveTop(m_image.height() - (backingStoreRect.y() + backingStoreRect.height()));
+    for (const QRect &viewLocalRect : clippedRegion) {
+        QPoint backingStoreOffset = viewLocalRect.topLeft() + offset;
+        QRect backingStoreRect(backingStoreOffset * devicePixelRatio, viewLocalRect.size() * devicePixelRatio);
+        if (graphicsContext.flipped) // Flip backingStoreRect to match graphics context
+            backingStoreRect.moveTop(m_image.height() - (backingStoreRect.y() + backingStoreRect.height()));
 
-            CGRect viewRect = viewLocalRect.toCGRect();
+        CGRect viewRect = viewLocalRect.toCGRect();
 
-            if (windowHasUnifiedToolbar())
-                NSDrawWindowBackground(viewRect);
+        if (windowHasUnifiedToolbar())
+            NSDrawWindowBackground(viewRect);
 
-            [backingStoreImage drawInRect:viewRect fromRect:backingStoreRect.toCGRect()
-                operation:compositingOperation fraction:1.0 respectFlipped:YES hints:nil];
+        [backingStoreImage drawInRect:viewRect fromRect:backingStoreRect.toCGRect()
+            operation:compositingOperation fraction:1.0 respectFlipped:YES hints:nil];
 
 #ifdef QT_DEBUG
-            if (Q_UNLIKELY(debugBackingStoreFlush)) {
-                [[NSColor colorWithCalibratedRed:drand48() green:drand48() blue:drand48() alpha:0.3] set];
-                [NSBezierPath fillRect:viewRect];
-
-                if (drawingOutsideOfDisplayCycle) {
-                    [[[NSColor magentaColor] colorWithAlphaComponent:0.5] set];
-                    [NSBezierPath strokeLineFromPoint:viewLocalRect.topLeft().toCGPoint()
-                        toPoint:viewLocalRect.bottomRight().toCGPoint()];
-                }
+        if (Q_UNLIKELY(debugBackingStoreFlush)) {
+            [[NSColor colorWithCalibratedRed:drand48() green:drand48() blue:drand48() alpha:0.3] set];
+            [NSBezierPath fillRect:viewRect];
+
+            if (drawingOutsideOfDisplayCycle) {
+                [[[NSColor magentaColor] colorWithAlphaComponent:0.5] set];
+                [NSBezierPath strokeLineFromPoint:viewLocalRect.topLeft().toCGPoint()
+                    toPoint:viewLocalRect.bottomRight().toCGPoint()];
             }
-#endif
         }
+#endif
+    }
 
-        // -------------------------------------------------------------------------
+    // -------------------------------------------------------------------------
 
-        if (shouldHandleViewLockManually)
-            [view unlockFocus];
+    if (shouldHandleViewLockManually)
+        [view unlockFocus];
 
-        if (drawingOutsideOfDisplayCycle) {
-            redrawRoundedBottomCorners([view convertRect:region.boundingRect().toCGRect() toView:nil]);
-            [view.window flushWindow];
-        }
+    if (drawingOutsideOfDisplayCycle) {
+        redrawRoundedBottomCorners([view convertRect:region.boundingRect().toCGRect() toView:nil]);
+        [view.window flushWindow];
     }
 
-    // Done flushing to either CALayer or NSWindow backingstore
+
+    // Done flushing to NSWindow backingstore
 
     QCocoaWindow *topLevelCocoaWindow = static_cast<QCocoaWindow *>(topLevelWindow->handle());
     if (Q_UNLIKELY(topLevelCocoaWindow->m_needsInvalidateShadow)) {
@@ -251,7 +237,7 @@ void QCocoaBackingStore::flush(QWindow *window, const QRegion &region, const QPo
 
     https://trac.webkit.org/changeset/85376/webkit
 */
-void QCocoaBackingStore::redrawRoundedBottomCorners(CGRect windowRect) const
+void QNSWindowBackingStore::redrawRoundedBottomCorners(CGRect windowRect) const
 {
 #if !defined(QT_APPLE_NO_PRIVATE_APIS)
     Q_ASSERT(this->window()->handle());
@@ -285,4 +271,345 @@ void QCocoaBackingStore::redrawRoundedBottomCorners(CGRect windowRect) const
 #endif
 }
 
+// ----------------------------------------------------------------------------
+
+// https://stackoverflow.com/a/52722575/2761869
+template<class R>
+struct backwards_t {
+  R r;
+  constexpr auto begin() const { using std::rbegin; return rbegin(r); }
+  constexpr auto begin() { using std::rbegin; return rbegin(r); }
+  constexpr auto end() const { using std::rend; return rend(r); }
+  constexpr auto end() { using std::rend; return rend(r); }
+};
+template<class R>
+constexpr backwards_t<R> backwards(R&& r) { return {std::forward<R>(r)}; }
+
+QCALayerBackingStore::QCALayerBackingStore(QWindow *window)
+    : QPlatformBackingStore(window)
+{
+    qCDebug(lcQpaBackingStore) << "Creating QCALayerBackingStore for" << window;
+    m_buffers.resize(1);
+}
+
+QCALayerBackingStore::~QCALayerBackingStore()
+{
+}
+
+void QCALayerBackingStore::resize(const QSize &size, const QRegion &staticContents)
+{
+    qCDebug(lcQpaBackingStore) << "Resize requested to" << size;
+
+    if (!staticContents.isNull())
+        qCWarning(lcQpaBackingStore) << "QCALayerBackingStore does not support static contents";
+
+    m_requestedSize = size;
+}
+
+void QCALayerBackingStore::beginPaint(const QRegion &region)
+{
+    Q_UNUSED(region);
+
+    QMacAutoReleasePool pool;
+
+    qCInfo(lcQpaBackingStore) << "Beginning paint of" << region << "into backingstore of" << m_requestedSize;
+
+    ensureBackBuffer(); // Find an unused back buffer, or reserve space for a new one
+
+    const bool bufferWasRecreated = recreateBackBufferIfNeeded();
+
+    m_buffers.back()->lock(QPlatformGraphicsBuffer::SWWriteAccess);
+
+    // Although undocumented, QBackingStore::beginPaint expects the painted region
+    // to be cleared before use if the window has a surface format with an alpha.
+    // Fresh IOSurfaces are already cleared, so we don't need to clear those.
+    if (!bufferWasRecreated && window()->format().hasAlpha()) {
+        qCDebug(lcQpaBackingStore) << "Clearing" << region << "before use";
+        QPainter painter(m_buffers.back()->asImage());
+        painter.setCompositionMode(QPainter::CompositionMode_Source);
+        for (const QRect &rect : region)
+            painter.fillRect(rect, Qt::transparent);
+    }
+
+    m_paintedRegion += region;
+}
+
+void QCALayerBackingStore::ensureBackBuffer()
+{
+    if (window()->format().swapBehavior() == QSurfaceFormat::SingleBuffer)
+        return;
+
+    // The current back buffer may have been assigned to a layer in a previous flush,
+    // but we deferred the swap. Do it now if the surface has been picked up by CA.
+    if (m_buffers.back() && m_buffers.back()->isInUse() && m_buffers.back() != m_buffers.front()) {
+        qCInfo(lcQpaBackingStore) << "Back buffer has been picked up by CA, swapping to front";
+        std::swap(m_buffers.back(), m_buffers.front());
+    }
+
+    if (Q_UNLIKELY(lcQpaBackingStore().isDebugEnabled())) {
+        // ┌───────┬───────┬───────┬─────┬──────┐
+        // │ front ┊ spare ┊ spare ┊ ... ┊ back │
+        // └───────┴───────┴───────┴─────┴──────┘
+        for (const auto &buffer : m_buffers) {
+            qCDebug(lcQpaBackingStore).nospace() << "  "
+                << (buffer == m_buffers.front() ? "front" :
+                    buffer == m_buffers.back()  ? " back" :
+                                                  "spare"
+                ) << ": " << buffer.get();
+        }
+    }
+
+    // Ensure our back buffer is ready to draw into. If not, find a buffer that
+    // is not in use, or reserve space for a new buffer if none can be found.
+    for (auto &buffer : backwards(m_buffers)) {
+        if (!buffer || !buffer->isInUse()) {
+            // Buffer is okey to use, swap if necessary
+            if (buffer != m_buffers.back())
+                std::swap(buffer, m_buffers.back());
+            qCDebug(lcQpaBackingStore) << "Using back buffer" << m_buffers.back().get();
+
+            static const int kMaxSwapChainDepth = 3;
+            if (m_buffers.size() > kMaxSwapChainDepth) {
+                qCDebug(lcQpaBackingStore) << "Reducing swap chain depth to" << kMaxSwapChainDepth;
+                m_buffers.erase(std::next(m_buffers.begin(), 1), std::prev(m_buffers.end(), 2));
+            }
+
+            break;
+        } else if (buffer == m_buffers.front()) {
+            // We've exhausted the available buffers, make room for a new one
+            const int swapChainDepth = m_buffers.size() + 1;
+            qCDebug(lcQpaBackingStore) << "Available buffers exhausted, increasing swap chain depth to" << swapChainDepth;
+            m_buffers.resize(swapChainDepth);
+            break;
+        }
+    }
+
+    Q_ASSERT(!m_buffers.back() || !m_buffers.back()->isInUse());
+}
+
+// Disabled until performance issue on 5K iMac Pro has been investigated further,
+// as rounding up during resize will typically result in full screen buffer sizes
+// and low frame rate also for smaller window sizes.
+#define USE_LAZY_BUFFER_ALLOCATION_DURING_LIVE_WINDOW_RESIZE 0
+
+bool QCALayerBackingStore::recreateBackBufferIfNeeded()
+{
+    const qreal devicePixelRatio = window()->devicePixelRatio();
+    QSize requestedBufferSize = m_requestedSize * devicePixelRatio;
+
+    const NSView *backingStoreView = static_cast<QCocoaWindow *>(window()->handle())->view();
+    Q_UNUSED(backingStoreView);
+
+    auto bufferSizeMismatch = [&](const QSize requested, const QSize actual) {
+#if USE_LAZY_BUFFER_ALLOCATION_DURING_LIVE_WINDOW_RESIZE
+        if (backingStoreView.inLiveResize) {
+            // Prevent over-eager buffer allocation during window resize by reusing larger buffers
+            return requested.width() > actual.width() || requested.height() > actual.height();
+        }
+#endif
+        return requested != actual;
+    };
+
+    if (!m_buffers.back() || bufferSizeMismatch(requestedBufferSize, m_buffers.back()->size())) {
+#if USE_LAZY_BUFFER_ALLOCATION_DURING_LIVE_WINDOW_RESIZE
+        if (backingStoreView.inLiveResize) {
+            // Prevent over-eager buffer allocation during window resize by rounding up
+            QSize nativeScreenSize = window()->screen()->geometry().size() * devicePixelRatio;
+            requestedBufferSize = QSize(qNextPowerOfTwo(requestedBufferSize.width()),
+                qNextPowerOfTwo(requestedBufferSize.height())).boundedTo(nativeScreenSize);
+        }
+#endif
+
+        qCInfo(lcQpaBackingStore) << "Creating surface of" << requestedBufferSize
+            << "based on requested" << m_requestedSize << "and dpr =" << devicePixelRatio;
+
+        static auto pixelFormat = QImage::toPixelFormat(QImage::Format_ARGB32_Premultiplied);
+
+        NSView *view = static_cast<QCocoaWindow *>(window()->handle())->view();
+        auto colorSpace = QCFType<CGColorSpaceRef>::constructFromGet(view.window.screen.colorSpace.CGColorSpace);
+
+        m_buffers.back().reset(new GraphicsBuffer(requestedBufferSize, devicePixelRatio, pixelFormat, colorSpace));
+        return true;
+    }
+
+    return false;
+}
+
+QPaintDevice *QCALayerBackingStore::paintDevice()
+{
+    Q_ASSERT(m_buffers.back());
+    return m_buffers.back()->asImage();
+}
+
+void QCALayerBackingStore::endPaint()
+{
+    qCInfo(lcQpaBackingStore) << "Paint ended with painted region" << m_paintedRegion;
+    m_buffers.back()->unlock();
+}
+
+void QCALayerBackingStore::flush(QWindow *flushedWindow, const QRegion &region, const QPoint &offset)
+{
+    Q_UNUSED(region);
+    Q_UNUSED(offset);
+
+    if (!prepareForFlush())
+        return;
+
+    QMacAutoReleasePool pool;
+
+    NSView *backingStoreView = static_cast<QCocoaWindow *>(window()->handle())->view();
+    NSView *flushedView = static_cast<QCocoaWindow *>(flushedWindow->handle())->view();
+
+    id backBufferSurface = (__bridge id)m_buffers.back()->surface();
+    if (flushedView.layer.contents == backBufferSurface) {
+        // We've managed to paint to the back buffer again before Core Animation had time
+        // to flush the transaction and persist the layer changes to the window server.
+        // The layer already knows about the back buffer, and we don't need to re-apply
+        // it to pick up the surface changes, so bail out early.
+        qCInfo(lcQpaBackingStore).nospace() << "Skipping flush of " << flushedView
+            << ", layer already reflects back buffer";
+        return;
+    }
+
+    // Trigger a new display cycle if there isn't one. This ensures that our layer updates
+    // are committed as part of a display-cycle instead of on the next runloop pass. This
+    // means CA won't try to throttle us if we flush too fast, and we'll coalesce our flush
+    // with other pending view and layer updates.
+    backingStoreView.window.viewsNeedDisplay = YES;
+
+    if (window()->format().swapBehavior() == QSurfaceFormat::SingleBuffer) {
+        // The private API [CALayer reloadValueForKeyPath:@"contents"] would be preferable,
+        // but barring any side effects or performance issues we opt for the hammer for now.
+        flushedView.layer.contents = nil;
+    }
+
+    qCInfo(lcQpaBackingStore) << "Flushing" << backBufferSurface
+         << "to" << flushedView.layer << "of" << flushedView;
+
+    flushedView.layer.contents = backBufferSurface;
+
+    if (flushedView != backingStoreView) {
+        const CGSize backingStoreSize = backingStoreView.bounds.size;
+        flushedView.layer.contentsRect = CGRectApplyAffineTransform(
+            [flushedView convertRect:flushedView.bounds toView:backingStoreView],
+            // The contentsRect is in unit coordinate system
+            CGAffineTransformMakeScale(1.0 / backingStoreSize.width, 1.0 / backingStoreSize.height));
+    }
+
+    // Since we may receive multiple flushes before a new frame is started, we do not
+    // swap any buffers just yet. Instead we check in the next beginPaint if the layer's
+    // surface is in use, and if so swap to an unused surface as the new back buffer.
+
+    // Note: Ideally CoreAnimation would mark a surface as in use the moment we assign
+    // it to a layer, but as that's not the case we may end up painting to the same back
+    // buffer once more if we are painting faster than CA can ship the surfaces over to
+    // the window server.
+}
+
+void QCALayerBackingStore::composeAndFlush(QWindow *window, const QRegion &region, const QPoint &offset,
+                                    QPlatformTextureList *textures, bool translucentBackground)
+{
+    if (!prepareForFlush())
+        return;
+
+    QPlatformBackingStore::composeAndFlush(window, region, offset, textures, translucentBackground);
+}
+
+QPlatformGraphicsBuffer *QCALayerBackingStore::graphicsBuffer() const
+{
+    return m_buffers.back().get();
+}
+
+bool QCALayerBackingStore::prepareForFlush()
+{
+    if (!m_buffers.back()) {
+        qCWarning(lcQpaBackingStore) << "Tried to flush backingstore without painting to it first";
+        return false;
+    }
+
+    // Update dirty state of buffers based on what was painted. The back buffer will be
+    // less dirty, since we painted to it, while other buffers will become more dirty.
+    // This allows us to minimize copies between front and back buffers on swap in the
+    // cases where the painted region overlaps with the previous frame (front buffer).
+    for (const auto &buffer : m_buffers) {
+        if (buffer == m_buffers.back())
+            buffer->dirtyRegion -= m_paintedRegion;
+        else
+            buffer->dirtyRegion += m_paintedRegion;
+    }
+
+    // After painting, the back buffer is only guaranteed to have content for the painted
+    // region, and may still have dirty areas that need to be synced up with the front buffer,
+    // if we have one. We know that the front buffer is always up to date.
+    if (!m_buffers.back()->dirtyRegion.isEmpty() && m_buffers.front() != m_buffers.back()) {
+        QRegion preserveRegion = m_buffers.back()->dirtyRegion;
+        qCDebug(lcQpaBackingStore) << "Preserving" << preserveRegion << "from front to back buffer";
+
+        m_buffers.front()->lock(QPlatformGraphicsBuffer::SWReadAccess);
+        const QImage *frontBuffer = m_buffers.front()->asImage();
+
+        const QRect frontSurfaceBounds(QPoint(0, 0), m_buffers.front()->size());
+        const qreal sourceDevicePixelRatio = frontBuffer->devicePixelRatio();
+
+        m_buffers.back()->lock(QPlatformGraphicsBuffer::SWWriteAccess);
+        QPainter painter(m_buffers.back()->asImage());
+        painter.setCompositionMode(QPainter::CompositionMode_Source);
+
+        // Let painter operate in device pixels, to make it easier to compare coordinates
+        const qreal targetDevicePixelRatio = painter.device()->devicePixelRatio();
+        painter.scale(1.0 / targetDevicePixelRatio, 1.0 / targetDevicePixelRatio);
+
+        for (const QRect &rect : preserveRegion) {
+            QRect sourceRect(rect.topLeft() * sourceDevicePixelRatio, rect.size() * sourceDevicePixelRatio);
+            QRect targetRect(rect.topLeft() * targetDevicePixelRatio, rect.size() * targetDevicePixelRatio);
+
+#ifdef QT_DEBUG
+            if (Q_UNLIKELY(!frontSurfaceBounds.contains(sourceRect.bottomRight()))) {
+                qCWarning(lcQpaBackingStore) << "Front buffer too small to preserve"
+                    << QRegion(sourceRect).subtracted(frontSurfaceBounds);
+            }
+#endif
+            painter.drawImage(targetRect, *frontBuffer, sourceRect);
+        }
+
+        m_buffers.back()->unlock();
+        m_buffers.front()->unlock();
+
+        // The back buffer is now completely in sync, ready to be presented
+        m_buffers.back()->dirtyRegion = QRegion();
+    }
+
+    // Prepare for another round of painting
+    m_paintedRegion = QRegion();
+
+    return true;
+}
+
+// ----------------------------------------------------------------------------
+
+QCALayerBackingStore::GraphicsBuffer::GraphicsBuffer(const QSize &size, qreal devicePixelRatio,
+                                const QPixelFormat &format, QCFType<CGColorSpaceRef> colorSpace)
+    : QIOSurfaceGraphicsBuffer(size, format, colorSpace)
+    , dirtyRegion(0, 0, size.width() / devicePixelRatio, size.height() / devicePixelRatio)
+    , m_devicePixelRatio(devicePixelRatio)
+{
+}
+
+QImage *QCALayerBackingStore::GraphicsBuffer::asImage()
+{
+    if (m_image.isNull()) {
+        qCDebug(lcQpaBackingStore) << "Setting up paint device for" << this;
+        CFRetain(surface());
+        m_image = QImage(data(), size().width(), size().height(),
+            bytesPerLine(), QImage::toImageFormat(format()),
+            QImageCleanupFunction(CFRelease), surface());
+        m_image.setDevicePixelRatio(m_devicePixelRatio);
+    }
+
+    Q_ASSERT_X(m_image.constBits() == data(), "QCALayerBackingStore",
+        "IOSurfaces should have have a fixed location in memory once created");
+
+    return &m_image;
+}
+
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/cocoa/qcocoaintegration.mm b/src/plugins/platforms/cocoa/qcocoaintegration.mm
index affbee35b7..fb3d05d3e4 100644
--- a/src/plugins/platforms/cocoa/qcocoaintegration.mm
+++ b/src/plugins/platforms/cocoa/qcocoaintegration.mm
@@ -244,7 +244,7 @@ QCocoaIntegration::~QCocoaIntegration()
 
     // Delete screens in reverse order to avoid crash in case of multiple screens
     while (!mScreens.isEmpty()) {
-        destroyScreen(mScreens.takeLast());
+        QWindowSystemInterface::handleScreenRemoved(mScreens.takeLast());
     }
 
     clearToolbars();
@@ -304,7 +304,7 @@ void QCocoaIntegration::updateScreens()
             screen = new QCocoaScreen(i);
             mScreens.append(screen);
             qCDebug(lcQpaScreen) << "Adding" << screen;
-            screenAdded(screen);
+            QWindowSystemInterface::handleScreenAdded(screen);
         }
         siblings << screen;
     }
@@ -321,7 +321,7 @@ void QCocoaIntegration::updateScreens()
         // Prevent stale references to NSScreen during destroy
         screen->m_screenIndex = -1;
         qCDebug(lcQpaScreen) << "Removing" << screen;
-        destroyScreen(screen);
+        QWindowSystemInterface::handleScreenRemoved(screen);
     }
 }
 
@@ -407,7 +407,16 @@ QPlatformOpenGLContext *QCocoaIntegration::createPlatformOpenGLContext(QOpenGLCo
 
 QPlatformBackingStore *QCocoaIntegration::createPlatformBackingStore(QWindow *window) const
 {
-    return new QCocoaBackingStore(window);
+    QCocoaWindow *platformWindow = static_cast<QCocoaWindow*>(window->handle());
+    if (!platformWindow) {
+        qWarning() << window << "must be created before being used with a backingstore";
+        return nullptr;
+    }
+
+    if (platformWindow->view().layer)
+        return new QCALayerBackingStore(window);
+    else
+        return new QNSWindowBackingStore(window);
 }
 
 QAbstractEventDispatcher *QCocoaIntegration::createEventDispatcher() const
diff --git a/src/plugins/platforms/cocoa/qiosurfacegraphicsbuffer.h b/src/plugins/platforms/cocoa/qiosurfacegraphicsbuffer.h
new file mode 100644
index 0000000000..872773cb7a
--- /dev/null
+++ b/src/plugins/platforms/cocoa/qiosurfacegraphicsbuffer.h
@@ -0,0 +1,77 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the plugins of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QIOSURFACEGRAPHICSBUFFER_H
+#define QIOSURFACEGRAPHICSBUFFER_H
+
+#include <qpa/qplatformgraphicsbuffer.h>
+#include <private/qcore_mac_p.h>
+
+QT_BEGIN_NAMESPACE
+
+class QIOSurfaceGraphicsBuffer : public QPlatformGraphicsBuffer
+{
+public:
+    QIOSurfaceGraphicsBuffer(const QSize &size, const QPixelFormat &format, QCFType<CGColorSpaceRef> colorSpace);
+    ~QIOSurfaceGraphicsBuffer();
+
+    const uchar *data() const override;
+    uchar *data() override;
+    int bytesPerLine() const override;
+
+    IOSurfaceRef surface();
+    bool isInUse() const;
+
+protected:
+    bool doLock(AccessTypes access, const QRect &rect) override;
+    void doUnlock() override;
+
+private:
+    QCFType<IOSurfaceRef> m_surface;
+
+    friend QDebug operator<<(QDebug, const QIOSurfaceGraphicsBuffer *);
+};
+
+#ifndef QT_NO_DEBUG_STREAM
+QDebug operator<<(QDebug, const QIOSurfaceGraphicsBuffer *);
+#endif
+
+QT_END_NAMESPACE
+
+#endif // QIOSURFACEGRAPHICSBUFFER_H
diff --git a/src/plugins/platforms/cocoa/qiosurfacegraphicsbuffer.mm b/src/plugins/platforms/cocoa/qiosurfacegraphicsbuffer.mm
new file mode 100644
index 0000000000..a367487e85
--- /dev/null
+++ b/src/plugins/platforms/cocoa/qiosurfacegraphicsbuffer.mm
@@ -0,0 +1,188 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the plugins of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qiosurfacegraphicsbuffer.h"
+
+#include <QtCore/qdebug.h>
+#include <QtCore/qloggingcategory.h>
+
+#include <CoreGraphics/CoreGraphics.h>
+#include <IOSurface/IOSurface.h>
+
+// CGColorSpaceCopyPropertyList is available on 10.12 and above,
+// but was only added in the 10.14 SDK, so declare it just in case.
+extern "C" CFPropertyListRef CGColorSpaceCopyPropertyList(CGColorSpaceRef space);
+
+QT_BEGIN_NAMESPACE
+
+Q_LOGGING_CATEGORY(lcQpaIOSurface, "qt.qpa.backingstore.iosurface");
+
+QIOSurfaceGraphicsBuffer::QIOSurfaceGraphicsBuffer(const QSize &size, const QPixelFormat &format, QCFType<CGColorSpaceRef> colorSpace)
+    : QPlatformGraphicsBuffer(size, format)
+{
+    const size_t width = size.width();
+    const size_t height = size.height();
+
+    Q_ASSERT(width <= IOSurfaceGetPropertyMaximum(kIOSurfaceWidth));
+    Q_ASSERT(height <= IOSurfaceGetPropertyMaximum(kIOSurfaceHeight));
+
+    static const char bytesPerElement = 4;
+
+    const size_t bytesPerRow = IOSurfaceAlignProperty(kIOSurfaceBytesPerRow, width * bytesPerElement);
+    const size_t totalBytes = IOSurfaceAlignProperty(kIOSurfaceAllocSize, height * bytesPerRow);
+
+    NSDictionary *options = @{
+        (id)kIOSurfaceWidth: @(width),
+        (id)kIOSurfaceHeight: @(height),
+        (id)kIOSurfacePixelFormat: @(unsigned('BGRA')),
+        (id)kIOSurfaceBytesPerElement: @(bytesPerElement),
+        (id)kIOSurfaceBytesPerRow: @(bytesPerRow),
+        (id)kIOSurfaceAllocSize: @(totalBytes),
+    };
+
+    m_surface = IOSurfaceCreate((CFDictionaryRef)options);
+    Q_ASSERT(m_surface);
+
+    Q_ASSERT(size_t(bytesPerLine()) == bytesPerRow);
+    Q_ASSERT(size_t(byteCount()) == totalBytes);
+
+    if (colorSpace) {
+        IOSurfaceSetValue(m_surface, CFSTR("IOSurfaceColorSpace"),
+            QCFType<CFPropertyListRef>(CGColorSpaceCopyPropertyList(colorSpace)));
+    }
+}
+
+QIOSurfaceGraphicsBuffer::~QIOSurfaceGraphicsBuffer()
+{
+}
+
+const uchar *QIOSurfaceGraphicsBuffer::data() const
+{
+    return (const uchar *)IOSurfaceGetBaseAddress(m_surface);
+}
+
+uchar *QIOSurfaceGraphicsBuffer::data()
+{
+    return (uchar *)IOSurfaceGetBaseAddress(m_surface);
+}
+
+int QIOSurfaceGraphicsBuffer::bytesPerLine() const
+{
+    return IOSurfaceGetBytesPerRow(m_surface);
+}
+
+IOSurfaceRef QIOSurfaceGraphicsBuffer::surface()
+{
+    return m_surface;
+}
+
+bool QIOSurfaceGraphicsBuffer::isInUse() const
+{
+    return IOSurfaceIsInUse(m_surface);
+}
+
+IOSurfaceLockOptions lockOptionsForAccess(QPlatformGraphicsBuffer::AccessTypes access)
+{
+    IOSurfaceLockOptions lockOptions = 0;
+    if (!(access & QPlatformGraphicsBuffer::SWWriteAccess))
+        lockOptions |= kIOSurfaceLockReadOnly;
+    return lockOptions;
+}
+
+bool QIOSurfaceGraphicsBuffer::doLock(AccessTypes access, const QRect &rect)
+{
+    Q_UNUSED(rect);
+    Q_ASSERT(!isLocked());
+
+    qCDebug(lcQpaIOSurface) << "Locking" << this << "for" << access;
+
+    // FIXME: Teach QPlatformBackingStore::composeAndFlush about non-2D texture
+    // targets, so that we can use CGLTexImageIOSurface2D to support TextureAccess.
+    if (access & (TextureAccess | HWCompositor))
+        return false;
+
+    auto lockOptions = lockOptionsForAccess(access);
+
+    // Try without read-back first
+    lockOptions |= kIOSurfaceLockAvoidSync;
+    kern_return_t ret = IOSurfaceLock(m_surface, lockOptions, nullptr);
+    if (ret == kIOSurfaceSuccess)
+        return true;
+
+    if (ret == kIOReturnCannotLock) {
+        qCWarning(lcQpaIOSurface) << "Locking of" << this << "requires read-back";
+        lockOptions ^= kIOSurfaceLockAvoidSync;
+        ret = IOSurfaceLock(m_surface, lockOptions, nullptr);
+    }
+
+    if (ret != kIOSurfaceSuccess) {
+        qCWarning(lcQpaIOSurface) << "Failed to lock" << this << ret;
+        return false;
+    }
+
+    return true;
+}
+
+void QIOSurfaceGraphicsBuffer::doUnlock()
+{
+    qCDebug(lcQpaIOSurface) << "Unlocking" << this << "from" << isLocked();
+
+    auto lockOptions = lockOptionsForAccess(isLocked());
+    bool success = IOSurfaceUnlock(m_surface, lockOptions, nullptr) == kIOSurfaceSuccess;
+    Q_ASSERT_X(success, "QIOSurfaceGraphicsBuffer", "Unlocking surface should succeed");
+}
+
+#ifndef QT_NO_DEBUG_STREAM
+QDebug operator<<(QDebug debug, const QIOSurfaceGraphicsBuffer *graphicsBuffer)
+{
+    QDebugStateSaver saver(debug);
+    debug.nospace();
+    debug << "QIOSurfaceGraphicsBuffer(" << (const void *)graphicsBuffer;
+    if (graphicsBuffer) {
+        debug << ", surface=" << graphicsBuffer->m_surface;
+        debug << ", size=" << graphicsBuffer->size();
+        debug << ", isLocked=" << bool(graphicsBuffer->isLocked());
+        debug << ", isInUse=" << graphicsBuffer->isInUse();
+    }
+    debug << ')';
+    return debug;
+}
+#endif // !QT_NO_DEBUG_STREAM
+
+QT_END_NAMESPACE
diff --git a/src/plugins/platforms/cocoa/qnsview_drawing.mm b/src/plugins/platforms/cocoa/qnsview_drawing.mm
index 6db5ed8bad..f7e14b7883 100644
--- a/src/plugins/platforms/cocoa/qnsview_drawing.mm
+++ b/src/plugins/platforms/cocoa/qnsview_drawing.mm
@@ -163,6 +163,13 @@
     return NSViewLayerContentsRedrawDuringViewResize;
 }
 
+- (NSViewLayerContentsPlacement)layerContentsPlacement
+{
+    // Always place the layer at top left without any automatic scaling,
+    // so that we can re-use larger layers when resizing a window down.
+    return NSViewLayerContentsPlacementTopLeft;
+}
+
 - (void)updateMetalLayerDrawableSize:(CAMetalLayer *)layer
 {
     CGSize drawableSize = layer.bounds.size;
diff --git a/src/plugins/platforms/directfb/qdirectfb_egl.cpp b/src/plugins/platforms/directfb/qdirectfb_egl.cpp
index dad553c890..d3c95f0b65 100644
--- a/src/plugins/platforms/directfb/qdirectfb_egl.cpp
+++ b/src/plugins/platforms/directfb/qdirectfb_egl.cpp
@@ -44,6 +44,7 @@
 
 #include <QtGui/QOpenGLContext>
 #include <qpa/qplatformopenglcontext.h>
+#include <qpa/qwindowsysteminterface.h>
 #include <QtGui/QScreen>
 
 #include <QtEglSupport/private/qeglplatformcontext_p.h>
@@ -248,7 +249,7 @@ QPlatformOpenGLContext *QDirectFbIntegrationEGL::createPlatformOpenGLContext(QOp
 void QDirectFbIntegrationEGL::initializeScreen()
 {
     m_primaryScreen.reset(new QDirectFbScreenEGL(0));
-    screenAdded(m_primaryScreen.data());
+    QWindowSystemInterface::handleScreenAdded(m_primaryScreen.data());
 }
 
 bool QDirectFbIntegrationEGL::hasCapability(QPlatformIntegration::Capability cap) const
diff --git a/src/plugins/platforms/directfb/qdirectfbintegration.cpp b/src/plugins/platforms/directfb/qdirectfbintegration.cpp
index cdf340da7a..73e308da53 100644
--- a/src/plugins/platforms/directfb/qdirectfbintegration.cpp
+++ b/src/plugins/platforms/directfb/qdirectfbintegration.cpp
@@ -56,6 +56,7 @@
 #include <QtCore/QThread>
 #include <QtCore/QAbstractEventDispatcher>
 #include <qpa/qplatforminputcontextfactory_p.h>
+#include <qpa/qwindowsysteminterface.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -113,7 +114,7 @@ void QDirectFbIntegration::initializeDirectFB()
 void QDirectFbIntegration::initializeScreen()
 {
     m_primaryScreen.reset(new QDirectFbScreen(0));
-    screenAdded(m_primaryScreen.data());
+    QWindowSystemInterface::handleScreenAdded(m_primaryScreen.data());
 }
 
 void QDirectFbIntegration::initializeInput()
diff --git a/src/plugins/platforms/eglfs/api/qeglfsdeviceintegration.cpp b/src/plugins/platforms/eglfs/api/qeglfsdeviceintegration.cpp
index 0a3a37863a..81bad45cd2 100644
--- a/src/plugins/platforms/eglfs/api/qeglfsdeviceintegration.cpp
+++ b/src/plugins/platforms/eglfs/api/qeglfsdeviceintegration.cpp
@@ -200,10 +200,8 @@ void QEglFSDeviceIntegration::screenInit()
 void QEglFSDeviceIntegration::screenDestroy()
 {
     QGuiApplication *app = qGuiApp;
-    QEglFSIntegration *platformIntegration = static_cast<QEglFSIntegration *>(
-        QGuiApplicationPrivate::platformIntegration());
     while (!app->screens().isEmpty())
-        platformIntegration->removeScreen(app->screens().constLast()->handle());
+        QWindowSystemInterface::handleScreenRemoved(app->screens().constLast()->handle());
 }
 
 QSizeF QEglFSDeviceIntegration::physicalScreenSize() const
diff --git a/src/plugins/platforms/eglfs/api/qeglfsintegration.cpp b/src/plugins/platforms/eglfs/api/qeglfsintegration.cpp
index 8ccb0ef2cd..48469b0f8c 100644
--- a/src/plugins/platforms/eglfs/api/qeglfsintegration.cpp
+++ b/src/plugins/platforms/eglfs/api/qeglfsintegration.cpp
@@ -120,16 +120,6 @@ QEglFSIntegration::QEglFSIntegration()
     initResources();
 }
 
-void QEglFSIntegration::addScreen(QPlatformScreen *screen, bool isPrimary)
-{
-    screenAdded(screen, isPrimary);
-}
-
-void QEglFSIntegration::removeScreen(QPlatformScreen *screen)
-{
-    destroyScreen(screen);
-}
-
 void QEglFSIntegration::initialize()
 {
     qt_egl_device_integration()->platformInit();
@@ -147,7 +137,7 @@ void QEglFSIntegration::initialize()
     m_vtHandler.reset(new QFbVtHandler);
 
     if (qt_egl_device_integration()->usesDefaultScreen())
-        addScreen(new QEglFSScreen(display()));
+        QWindowSystemInterface::handleScreenAdded(new QEglFSScreen(display()));
     else
         qt_egl_device_integration()->screenInit();
 
diff --git a/src/plugins/platforms/eglfs/api/qeglfsintegration_p.h b/src/plugins/platforms/eglfs/api/qeglfsintegration_p.h
index 4b4585d33c..898b322834 100644
--- a/src/plugins/platforms/eglfs/api/qeglfsintegration_p.h
+++ b/src/plugins/platforms/eglfs/api/qeglfsintegration_p.h
@@ -103,9 +103,6 @@ public:
 
     QFbVtHandler *vtHandler() { return m_vtHandler.data(); }
 
-    void addScreen(QPlatformScreen *screen, bool isPrimary = false);
-    void removeScreen(QPlatformScreen *screen);
-
 private:
     EGLNativeDisplayType nativeDisplay() const;
     void createInputHandlers();
diff --git a/src/plugins/platforms/eglfs/deviceintegration/eglfs_emu/qeglfsemulatorintegration.cpp b/src/plugins/platforms/eglfs/deviceintegration/eglfs_emu/qeglfsemulatorintegration.cpp
index 5e2708e958..cb7844aff0 100644
--- a/src/plugins/platforms/eglfs/deviceintegration/eglfs_emu/qeglfsemulatorintegration.cpp
+++ b/src/plugins/platforms/eglfs/deviceintegration/eglfs_emu/qeglfsemulatorintegration.cpp
@@ -45,6 +45,8 @@
 #include <QtEglSupport/private/qeglconvenience_p.h>
 #include <QtEglSupport/private/qeglplatformcontext_p.h>
 
+#include <qpa/qwindowsysteminterface.h>
+
 #include <QtCore/QJsonDocument>
 #include <QtCore/QJsonArray>
 #include <QtCore/QJsonParseError>
@@ -80,8 +82,6 @@ bool QEglFSEmulatorIntegration::usesDefaultScreen()
 
 void QEglFSEmulatorIntegration::screenInit()
 {
-    QEglFSIntegration *integration = static_cast<QEglFSIntegration *>(QGuiApplicationPrivate::platformIntegration());
-
     // Use qgsGetDisplays() call to retrieve the available screens from the Emulator
     if (getDisplays) {
         QByteArray displaysInfo = getDisplays();
@@ -93,7 +93,7 @@ void QEglFSEmulatorIntegration::screenInit()
                 QJsonArray screenArray = displaysDocument.array();
                 for (auto screenValue : screenArray) {
                     if (screenValue.isObject())
-                        integration->addScreen(new QEglFSEmulatorScreen(screenValue.toObject()));
+                        QWindowSystemInterface::handleScreenAdded(new QEglFSEmulatorScreen(screenValue.toObject()));
                 }
             }
         } else {
diff --git a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_egldevice/qeglfskmsegldeviceintegration.cpp b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_egldevice/qeglfskmsegldeviceintegration.cpp
index ab39af6b80..ecdfb352ab 100644
--- a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_egldevice/qeglfskmsegldeviceintegration.cpp
+++ b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_egldevice/qeglfskmsegldeviceintegration.cpp
@@ -260,7 +260,7 @@ QKmsDevice *QEglFSKmsEglDeviceIntegration::createDevice()
     if (Q_UNLIKELY(!deviceName))
         qFatal("Failed to query device name from EGLDevice");
 
-    return new QEglFSKmsEglDevice(this, screenConfig(), deviceName);
+    return new QEglFSKmsEglDevice(this, screenConfig(), QLatin1String(deviceName));
 }
 
 bool QEglFSKmsEglDeviceIntegration::query_egl_device()
diff --git a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_support/qeglfskmsdevice.cpp b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_support/qeglfskmsdevice.cpp
index b073577797..4f0b0d7725 100644
--- a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_support/qeglfskmsdevice.cpp
+++ b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_support/qeglfskmsdevice.cpp
@@ -58,7 +58,7 @@ void QEglFSKmsDevice::registerScreen(QPlatformScreen *screen,
     QEglFSKmsScreen *s = static_cast<QEglFSKmsScreen *>(screen);
     s->setVirtualPosition(virtualPos);
     s->setVirtualSiblings(virtualSiblings);
-    static_cast<QEglFSIntegration *>(QGuiApplicationPrivate::platformIntegration())->addScreen(s, isPrimary);
+    QWindowSystemInterface::handleScreenAdded(s, isPrimary);
 }
 
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/haiku/qhaikuintegration.cpp b/src/plugins/platforms/haiku/qhaikuintegration.cpp
index 8bd2171794..44df6ae8f5 100644
--- a/src/plugins/platforms/haiku/qhaikuintegration.cpp
+++ b/src/plugins/platforms/haiku/qhaikuintegration.cpp
@@ -49,6 +49,7 @@
 #include <QCoreApplication>
 #include <QFileInfo>
 #include <qpa/qplatformwindow.h>
+#include <qpa/qwindowsysteminterface.h>
 #include <QtEventDispatcherSupport/private/qgenericunixeventdispatcher_p.h>
 
 #include <Application.h>
@@ -81,12 +82,12 @@ QHaikuIntegration::QHaikuIntegration(const QStringList &parameters)
     m_services = new QHaikuServices;
 
     // notify system about available screen
-    screenAdded(m_screen);
+    QWindowSystemInterface::handleScreenAdded(m_screen);
 }
 
 QHaikuIntegration::~QHaikuIntegration()
 {
-    destroyScreen(m_screen);
+    QWindowSystemInterface::handleScreenRemoved(m_screen);
     m_screen = nullptr;
 
     delete m_services;
diff --git a/src/plugins/platforms/integrity/qintegrityfbintegration.cpp b/src/plugins/platforms/integrity/qintegrityfbintegration.cpp
index ae802bb1fa..3ad31dc562 100644
--- a/src/plugins/platforms/integrity/qintegrityfbintegration.cpp
+++ b/src/plugins/platforms/integrity/qintegrityfbintegration.cpp
@@ -51,7 +51,7 @@
 
 #include <QtGui/private/qguiapplication_p.h>
 #include <qpa/qplatforminputcontextfactory_p.h>
-
+#include <qpa/qwindowsysteminterface.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -64,13 +64,13 @@ QIntegrityFbIntegration::QIntegrityFbIntegration(const QStringList &paramList)
 
 QIntegrityFbIntegration::~QIntegrityFbIntegration()
 {
-    destroyScreen(m_primaryScreen);
+    QWindowSystemInterface::handleScreenRemoved(m_primaryScreen);
 }
 
 void QIntegrityFbIntegration::initialize()
 {
     if (m_primaryScreen->initialize())
-        screenAdded(m_primaryScreen);
+        QWindowSystemInterface::handleScreenAdded(m_primaryScreen);
     else
         qWarning("integrityfb: Failed to initialize screen");
 
diff --git a/src/plugins/platforms/ios/qiosintegration.h b/src/plugins/platforms/ios/qiosintegration.h
index 818250fcee..eeb44b54d3 100644
--- a/src/plugins/platforms/ios/qiosintegration.h
+++ b/src/plugins/platforms/ios/qiosintegration.h
@@ -92,10 +92,6 @@ public:
     QPlatformAccessibility *accessibility() const override;
 #endif
 
-    // Called from Objective-C class QIOSScreenTracker, which can't be friended
-    void addScreen(QPlatformScreen *screen) { screenAdded(screen); }
-    void destroyScreen(QPlatformScreen *screen) { QPlatformIntegration::destroyScreen(screen); }
-
     void beep() const override;
 
     static QIOSIntegration *instance();
diff --git a/src/plugins/platforms/ios/qiosintegration.mm b/src/plugins/platforms/ios/qiosintegration.mm
index bec8354fcc..9eca0eaad3 100644
--- a/src/plugins/platforms/ios/qiosintegration.mm
+++ b/src/plugins/platforms/ios/qiosintegration.mm
@@ -107,7 +107,7 @@ void QIOSIntegration::initialize()
     }
 
     for (UIScreen *screen in screens)
-        addScreen(new QIOSScreen(screen));
+        QWindowSystemInterface::handleScreenAdded(new QIOSScreen(screen));
 
     // Depends on a primary screen being present
     m_inputContext = new QIOSInputContext;
@@ -143,7 +143,7 @@ QIOSIntegration::~QIOSIntegration()
     m_inputContext = 0;
 
     foreach (QScreen *screen, QGuiApplication::screens())
-        destroyScreen(screen->handle());
+        QWindowSystemInterface::handleScreenRemoved(screen->handle());
 
     delete m_platformServices;
     m_platformServices = 0;
diff --git a/src/plugins/platforms/ios/qiosscreen.mm b/src/plugins/platforms/ios/qiosscreen.mm
index 4f753be21a..9aba658479 100644
--- a/src/plugins/platforms/ios/qiosscreen.mm
+++ b/src/plugins/platforms/ios/qiosscreen.mm
@@ -50,6 +50,7 @@
 
 #include <QtGui/private/qwindow_p.h>
 #include <private/qcoregraphics_p.h>
+#include <qpa/qwindowsysteminterface.h>
 
 #include <sys/sysctl.h>
 
@@ -105,10 +106,10 @@ static QIOSScreen* qtPlatformScreenFor(UIScreen *uiScreen)
 
 + (void)screenConnected:(NSNotification*)notification
 {
-    QIOSIntegration *integration = QIOSIntegration::instance();
-    Q_ASSERT_X(integration, Q_FUNC_INFO, "Screen connected before QIOSIntegration creation");
+    Q_ASSERT_X(QIOSIntegration::instance(), Q_FUNC_INFO,
+        "Screen connected before QIOSIntegration creation");
 
-    integration->addScreen(new QIOSScreen([notification object]));
+    QWindowSystemInterface::handleScreenAdded(new QIOSScreen([notification object]));
 }
 
 + (void)screenDisconnected:(NSNotification*)notification
@@ -116,8 +117,7 @@ static QIOSScreen* qtPlatformScreenFor(UIScreen *uiScreen)
     QIOSScreen *screen = qtPlatformScreenFor([notification object]);
     Q_ASSERT_X(screen, Q_FUNC_INFO, "Screen disconnected that we didn't know about");
 
-    QIOSIntegration *integration = QIOSIntegration::instance();
-    integration->destroyScreen(screen);
+    QWindowSystemInterface::handleScreenRemoved(screen);
 }
 
 + (void)screenModeChanged:(NSNotification*)notification
diff --git a/src/plugins/platforms/linuxfb/qlinuxfbintegration.cpp b/src/plugins/platforms/linuxfb/qlinuxfbintegration.cpp
index 9e38900bcd..68843aa4c5 100644
--- a/src/plugins/platforms/linuxfb/qlinuxfbintegration.cpp
+++ b/src/plugins/platforms/linuxfb/qlinuxfbintegration.cpp
@@ -54,6 +54,7 @@
 
 #include <QtGui/private/qguiapplication_p.h>
 #include <qpa/qplatforminputcontextfactory_p.h>
+#include <qpa/qwindowsysteminterface.h>
 
 #if QT_CONFIG(libinput)
 #include <QtInputSupport/private/qlibinputhandler_p.h>
@@ -89,13 +90,13 @@ QLinuxFbIntegration::QLinuxFbIntegration(const QStringList &paramList)
 
 QLinuxFbIntegration::~QLinuxFbIntegration()
 {
-    destroyScreen(m_primaryScreen);
+    QWindowSystemInterface::handleScreenRemoved(m_primaryScreen);
 }
 
 void QLinuxFbIntegration::initialize()
 {
     if (m_primaryScreen->initialize())
-        screenAdded(m_primaryScreen);
+        QWindowSystemInterface::handleScreenAdded(m_primaryScreen);
     else
         qWarning("linuxfb: Failed to initialize screen");
 
diff --git a/src/plugins/platforms/minimal/qminimalintegration.cpp b/src/plugins/platforms/minimal/qminimalintegration.cpp
index 0c04608fca..f457f69f11 100644
--- a/src/plugins/platforms/minimal/qminimalintegration.cpp
+++ b/src/plugins/platforms/minimal/qminimalintegration.cpp
@@ -43,6 +43,7 @@
 #include <QtGui/private/qpixmap_raster_p.h>
 #include <QtGui/private/qguiapplication_p.h>
 #include <qpa/qplatformwindow.h>
+#include <qpa/qwindowsysteminterface.h>
 
 #include <QtFontDatabaseSupport/private/qfreetypefontdatabase_p.h>
 #if defined(Q_OS_WINRT)
@@ -108,7 +109,7 @@ QMinimalIntegration::QMinimalIntegration(const QStringList &parameters)
     mPrimaryScreen->mDepth = 32;
     mPrimaryScreen->mFormat = QImage::Format_ARGB32_Premultiplied;
 
-    screenAdded(mPrimaryScreen);
+    QWindowSystemInterface::handleScreenAdded(mPrimaryScreen);
 }
 
 QMinimalIntegration::~QMinimalIntegration()
diff --git a/src/plugins/platforms/minimalegl/qminimaleglintegration.cpp b/src/plugins/platforms/minimalegl/qminimaleglintegration.cpp
index da58441d67..a0d35a80cd 100644
--- a/src/plugins/platforms/minimalegl/qminimaleglintegration.cpp
+++ b/src/plugins/platforms/minimalegl/qminimaleglintegration.cpp
@@ -58,6 +58,7 @@
 #include <QtGui/QSurfaceFormat>
 #include <QtGui/QOpenGLContext>
 #include <QtGui/QScreen>
+#include <qpa/qwindowsysteminterface.h>
 
 // this is where EGL headers are pulled in, make sure it is last
 #include "qminimaleglscreen.h"
@@ -90,7 +91,7 @@ protected:
 QMinimalEglIntegration::QMinimalEglIntegration()
     : mFontDb(new QGenericUnixFontDatabase()), mScreen(new QMinimalEglScreen(EGL_DEFAULT_DISPLAY))
 {
-    screenAdded(mScreen);
+    QWindowSystemInterface::handleScreenAdded(mScreen);
 
 #ifdef QEGL_EXTRA_DEBUG
     qWarning("QMinimalEglIntegration\n");
@@ -99,7 +100,7 @@ QMinimalEglIntegration::QMinimalEglIntegration()
 
 QMinimalEglIntegration::~QMinimalEglIntegration()
 {
-    destroyScreen(mScreen);
+    QWindowSystemInterface::handleScreenRemoved(mScreen);
     delete mFontDb;
 }
 
diff --git a/src/plugins/platforms/mirclient/qmirclientintegration.cpp b/src/plugins/platforms/mirclient/qmirclientintegration.cpp
index eef96ee3de..d2b1dbee0d 100644
--- a/src/plugins/platforms/mirclient/qmirclientintegration.cpp
+++ b/src/plugins/platforms/mirclient/qmirclientintegration.cpp
@@ -58,6 +58,7 @@
 #include <qpa/qplatformnativeinterface.h>
 #include <qpa/qplatforminputcontextfactory_p.h>
 #include <qpa/qplatforminputcontext.h>
+#include <qpa/qwindowsysteminterface.h>
 #include <QtEglSupport/private/qeglconvenience_p.h>
 #include <QtEglSupport/private/qeglpbuffer_p.h>
 #include <QtFontDatabaseSupport/private/qgenericunixfontdatabase_p.h>
@@ -149,12 +150,12 @@ void QMirClientClientIntegration::initialize()
     // Init the ScreenObserver
     mScreenObserver.reset(new QMirClientScreenObserver(mMirConnection));
     connect(mScreenObserver.data(), &QMirClientScreenObserver::screenAdded,
-            [this](QMirClientScreen *screen) { this->screenAdded(screen); });
+            [this](QMirClientScreen *screen) { QWindowSystemInterface::handleScreenAdded(screen); });
     connect(mScreenObserver.data(), &QMirClientScreenObserver::screenRemoved,
                      this, &QMirClientClientIntegration::destroyScreen);
 
     Q_FOREACH (auto screen, mScreenObserver->screens()) {
-        screenAdded(screen);
+        QWindowSystemInterface::handleScreenAdded(screen);
     }
 
     // Initialize input.
@@ -392,7 +393,7 @@ void QMirClientClientIntegration::destroyScreen(QMirClientScreen *screen)
 #if QT_VERSION < QT_VERSION_CHECK(5, 5, 0)
     delete screen;
 #else
-    QPlatformIntegration::destroyScreen(screen);
+    QWindowSystemInterface::handleScreenRemoved(screen);
 #endif
 }
 
diff --git a/src/plugins/platforms/offscreen/qoffscreenintegration.cpp b/src/plugins/platforms/offscreen/qoffscreenintegration.cpp
index f2933b7179..869e9228cd 100644
--- a/src/plugins/platforms/offscreen/qoffscreenintegration.cpp
+++ b/src/plugins/platforms/offscreen/qoffscreenintegration.cpp
@@ -63,6 +63,7 @@
 #include <qpa/qplatforminputcontextfactory_p.h>
 #include <qpa/qplatforminputcontext.h>
 #include <qpa/qplatformtheme.h>
+#include <qpa/qwindowsysteminterface.h>
 
 #include <qpa/qplatformservices.h>
 
@@ -121,7 +122,7 @@ QOffscreenIntegration::QOffscreenIntegration()
 #endif
     m_services.reset(new QPlatformServices);
 
-    screenAdded(new QOffscreenScreen);
+    QWindowSystemInterface::handleScreenAdded(new QOffscreenScreen);
 }
 
 QOffscreenIntegration::~QOffscreenIntegration()
diff --git a/src/plugins/platforms/openwfd/qopenwfdintegration.cpp b/src/plugins/platforms/openwfd/qopenwfdintegration.cpp
index 4850ca2e45..c5dc40a206 100644
--- a/src/plugins/platforms/openwfd/qopenwfdintegration.cpp
+++ b/src/plugins/platforms/openwfd/qopenwfdintegration.cpp
@@ -50,6 +50,7 @@
 #include <QtGui/private/qguiapplication_p.h>
 #include <QtGui/QOpenGLContext>
 #include <QtGui/QScreen>
+#include <qpa/qwindowsysteminterface.h>
 
 #include <QtEventDispatcherSupport/private/qgenericunixeventdispatcher_p.h>
 #include <QtFontDatabaseSupport/private/qgenericunixfontdatabase_p.h>
@@ -135,13 +136,3 @@ QPlatformPrinterSupport * QOpenWFDIntegration::printerSupport() const
 {
     return mPrinterSupport;
 }
-
-void QOpenWFDIntegration::addScreen(QOpenWFDScreen *screen)
-{
-    screenAdded(screen);
-}
-
-void QOpenWFDIntegration::destroyScreen(QOpenWFDScreen *screen)
-{
-    QPlatformIntegration::destroyScreen(screen);
-}
diff --git a/src/plugins/platforms/openwfd/qopenwfdintegration.h b/src/plugins/platforms/openwfd/qopenwfdintegration.h
index 1ce1001bed..444aaccaaf 100644
--- a/src/plugins/platforms/openwfd/qopenwfdintegration.h
+++ b/src/plugins/platforms/openwfd/qopenwfdintegration.h
@@ -68,8 +68,6 @@ public:
 
     QPlatformPrinterSupport *printerSupport() const;
 
-    void addScreen(QOpenWFDScreen *screen);
-    void destroyScreen(QOpenWFDScreen *screen);
 private:
     QList<QPlatformScreen *> mScreens;
     QList<QOpenWFDDevice *>mDevices;
diff --git a/src/plugins/platforms/openwfd/qopenwfdport.cpp b/src/plugins/platforms/openwfd/qopenwfdport.cpp
index 33254fe83c..34b4439958 100644
--- a/src/plugins/platforms/openwfd/qopenwfdport.cpp
+++ b/src/plugins/platforms/openwfd/qopenwfdport.cpp
@@ -133,7 +133,7 @@ void QOpenWFDPort::attach()
     wfdBindPipelineToPort(mDevice->handle(),mPort,mPipeline);
 
     mScreen = new QOpenWFDScreen(this);
-    mDevice->integration()->addScreen(mScreen);
+    QWindowSystemInterface::handleScreenAdded(mScreen);
     mAttached = true;
 }
 
@@ -145,7 +145,7 @@ void QOpenWFDPort::detach()
     mAttached = false;
     mOn = false;
 
-    mDevice->integration()->destroyScreen(mScreen);
+    QWindowSystemInterface::handleScreenRemoved(mScreen);
 
     wfdDestroyPipeline(mDevice->handle(),mPipeline);
     mPipelineId = WFD_INVALID_PIPELINE_ID;
diff --git a/src/plugins/platforms/qnx/qqnxintegration.cpp b/src/plugins/platforms/qnx/qqnxintegration.cpp
index a996e765c4..a45dcabeb7 100644
--- a/src/plugins/platforms/qnx/qqnxintegration.cpp
+++ b/src/plugins/platforms/qnx/qqnxintegration.cpp
@@ -649,7 +649,7 @@ void QQnxIntegration::createDisplay(screen_display_t display, bool isPrimary)
 {
     QQnxScreen *screen = new QQnxScreen(m_screenContext, display, isPrimary);
     m_screens.append(screen);
-    screenAdded(screen);
+    QWindowSystemInterface::handleScreenAdded(screen);
     screen->adjustOrientation();
 
     QObject::connect(m_screenEventHandler, SIGNAL(newWindowCreated(void*)),
@@ -669,14 +669,14 @@ void QQnxIntegration::removeDisplay(QQnxScreen *screen)
     Q_CHECK_PTR(screen);
     Q_ASSERT(m_screens.contains(screen));
     m_screens.removeAll(screen);
-    destroyScreen(screen);
+    QWindowSystemInterface::handleScreenRemoved(screen);
 }
 
 void QQnxIntegration::destroyDisplays()
 {
     qIntegrationDebug();
     Q_FOREACH (QQnxScreen *screen, m_screens) {
-        QPlatformIntegration::destroyScreen(screen);
+        QWindowSystemInterface::handleScreenRemoved(screen);
     }
     m_screens.clear();
 }
diff --git a/src/plugins/platforms/vnc/qvncintegration.cpp b/src/plugins/platforms/vnc/qvncintegration.cpp
index 1e2cf6292c..c7a796464a 100644
--- a/src/plugins/platforms/vnc/qvncintegration.cpp
+++ b/src/plugins/platforms/vnc/qvncintegration.cpp
@@ -52,6 +52,7 @@
 #include <QtGui/private/qguiapplication_p.h>
 #include <qpa/qplatforminputcontextfactory_p.h>
 #include <private/qinputdevicemanager_p_p.h>
+#include <qpa/qwindowsysteminterface.h>
 
 #include <QtCore/QRegularExpression>
 
@@ -77,13 +78,13 @@ QVncIntegration::QVncIntegration(const QStringList &paramList)
 QVncIntegration::~QVncIntegration()
 {
     delete m_server;
-    destroyScreen(m_primaryScreen);
+    QWindowSystemInterface::handleScreenRemoved(m_primaryScreen);
 }
 
 void QVncIntegration::initialize()
 {
     if (m_primaryScreen->initialize())
-        screenAdded(m_primaryScreen);
+        QWindowSystemInterface::handleScreenAdded(m_primaryScreen);
     else
         qWarning("vnc: Failed to initialize screen");
 
diff --git a/src/plugins/platforms/wasm/qwasmintegration.cpp b/src/plugins/platforms/wasm/qwasmintegration.cpp
index 1964cefdad..499a82adbd 100644
--- a/src/plugins/platforms/wasm/qwasmintegration.cpp
+++ b/src/plugins/platforms/wasm/qwasmintegration.cpp
@@ -98,7 +98,10 @@ QWasmIntegration::QWasmIntegration()
 QWasmIntegration::~QWasmIntegration()
 {
     delete m_fontDb;
-    qDeleteAll(m_screens);
+
+    while (!m_screens.isEmpty())
+        QWindowSystemInterface::handleScreenRemoved(m_screens.takeLast());
+
     s_instance = nullptr;
 }
 
@@ -191,7 +194,7 @@ void QWasmIntegration::addScreen(const QString &canvasId)
     QWasmScreen *screen = new QWasmScreen(canvasId);
     m_clipboard->installEventHandlers(canvasId);
     m_screens.append(screen);
-    screenAdded(screen);
+    QWindowSystemInterface::handleScreenAdded(screen);
 }
 
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/windows/qwindowsintegration.h b/src/plugins/platforms/windows/qwindowsintegration.h
index da86852766..e28b2c2fb3 100644
--- a/src/plugins/platforms/windows/qwindowsintegration.h
+++ b/src/plugins/platforms/windows/qwindowsintegration.h
@@ -107,9 +107,6 @@ public:
 
     static QWindowsIntegration *instance() { return m_instance; }
 
-    inline void emitScreenAdded(QPlatformScreen *s, bool isPrimary = false) { screenAdded(s, isPrimary); }
-    inline void emitDestroyScreen(QPlatformScreen *s) { destroyScreen(s); }
-
     unsigned options() const;
 
     void beep() const override;
diff --git a/src/plugins/platforms/windows/qwindowsscreen.cpp b/src/plugins/platforms/windows/qwindowsscreen.cpp
index a161dc46e9..0520f88935 100644
--- a/src/plugins/platforms/windows/qwindowsscreen.cpp
+++ b/src/plugins/platforms/windows/qwindowsscreen.cpp
@@ -121,7 +121,7 @@ BOOL QT_WIN_CALLBACK monitorEnumCallback(HMONITOR hMonitor, HDC, LPRECT, LPARAM
     QWindowsScreenData data;
     if (monitorData(hMonitor, &data)) {
         WindowsScreenDataList *result = reinterpret_cast<WindowsScreenDataList *>(p);
-        // QPlatformIntegration::screenAdded() documentation specifies that first
+        // QWindowSystemInterface::handleScreenAdded() documentation specifies that first
         // added screen will be the primary screen, so order accordingly.
         // Note that the side effect of this policy is that there is no way to change primary
         // screen reported by Qt, unless we want to delete all existing screens and add them
@@ -521,7 +521,7 @@ void QWindowsScreenManager::removeScreen(int index)
         if (movedWindowCount)
             QWindowSystemInterface::flushWindowSystemEvents();
     }
-    QWindowsIntegration::instance()->emitDestroyScreen(m_screens.takeAt(index));
+    QWindowSystemInterface::handleScreenRemoved(m_screens.takeAt(index));
 }
 
 /*!
@@ -541,7 +541,7 @@ bool QWindowsScreenManager::handleScreenChanges()
         } else {
             QWindowsScreen *newScreen = new QWindowsScreen(newData);
             m_screens.push_back(newScreen);
-            QWindowsIntegration::instance()->emitScreenAdded(newScreen,
+            QWindowSystemInterface::handleScreenAdded(newScreen,
                                                              newData.flags & QWindowsScreenData::PrimaryScreen);
             qCDebug(lcQpaWindows) << "New Monitor: " << newData;
         }    // exists
@@ -561,7 +561,7 @@ void QWindowsScreenManager::clearScreens()
 {
     // Delete screens in reverse order to avoid crash in case of multiple screens
     while (!m_screens.isEmpty())
-        QWindowsIntegration::instance()->emitDestroyScreen(m_screens.takeLast());
+        QWindowSystemInterface::handleScreenRemoved(m_screens.takeLast());
 }
 
 const QWindowsScreen *QWindowsScreenManager::screenAtDp(const QPoint &p) const
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 8bf090bf03..07fd2916c2 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -1759,15 +1759,12 @@ void QWindowsWindow::checkForScreenChanged()
 
     QPlatformScreen *currentScreen = screen();
     const auto &screenManager = QWindowsContext::instance()->screenManager();
-    // QTBUG-62971: When dragging a window by its border, detect by mouse position
-    // to prevent it from oscillating between screens when it resizes
-    const QWindowsScreen *newScreen = testFlag(ResizeMoveActive)
-        ? screenManager.screenAtDp(QWindowsCursor::mousePosition())
-        : screenManager.screenForHwnd(m_data.hwnd);
+    const QWindowsScreen *newScreen = screenManager.screenForHwnd(m_data.hwnd);
     if (newScreen != nullptr && newScreen != currentScreen) {
         qCDebug(lcQpaWindows).noquote().nospace() << __FUNCTION__
             << ' ' << window() << " \"" << currentScreen->name()
             << "\"->\"" << newScreen->name() << '"';
+        setFlag(SynchronousGeometryChangeEvent);
         QWindowSystemInterface::handleWindowScreenChanged(window(), newScreen->screen());
     }
 }
@@ -1786,11 +1783,14 @@ void QWindowsWindow::handleGeometryChange()
         fireExpose(QRect(QPoint(0, 0), m_data.geometry.size()), true);
     }
 
+    const bool wasSync = testFlag(SynchronousGeometryChangeEvent);
     checkForScreenChanged();
 
     if (testFlag(SynchronousGeometryChangeEvent))
         QWindowSystemInterface::flushWindowSystemEvents(QEventLoop::ExcludeUserInputEvents);
 
+    if (!wasSync)
+        clearFlag(SynchronousGeometryChangeEvent);
     qCDebug(lcQpaEvents) << __FUNCTION__ << this << window() << m_data.geometry;
 }
 
diff --git a/src/plugins/platforms/winrt/qwinrtintegration.cpp b/src/plugins/platforms/winrt/qwinrtintegration.cpp
index 78cbc3aec3..27d3746933 100644
--- a/src/plugins/platforms/winrt/qwinrtintegration.cpp
+++ b/src/plugins/platforms/winrt/qwinrtintegration.cpp
@@ -133,7 +133,7 @@ QWinRTIntegration::QWinRTIntegration() : d_ptr(new QWinRTIntegrationPrivate)
     });
     d->inputContext.reset(new QWinRTInputContext(d->mainScreen));
 
-    screenAdded(d->mainScreen);
+    QWindowSystemInterface::handleScreenAdded(d->mainScreen);
     d->platformServices = new QWinRTServices;
     d->clipboard = new QWinRTClipboard;
 #if QT_CONFIG(accessibility)
@@ -154,7 +154,7 @@ QWinRTIntegration::~QWinRTIntegration()
         Q_ASSERT_SUCCEEDED(hr);
     }
 
-    destroyScreen(d->mainScreen);
+    QWindowSystemInterface::handleScreenRemoved(d->mainScreen);
     Windows::Foundation::Uninitialize();
 }
 
diff --git a/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.cpp b/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.cpp
index d42a33c22b..476de6d1e5 100644
--- a/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.cpp
+++ b/src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.cpp
@@ -652,6 +652,12 @@ static const char *qglx_threadedgl_blacklist_renderer[] = {
     0
 };
 
+static const char *qglx_threadedgl_blacklist_vendor[] = {
+    "llvmpipe",                             // QTCREATORBUG-10666
+    "nouveau",                              // https://bugs.freedesktop.org/show_bug.cgi?id=91632
+    nullptr
+};
+
 void QGLXContext::queryDummyContext()
 {
     if (m_queriedDummyContext)
@@ -710,6 +716,18 @@ void QGLXContext::queryDummyContext()
             }
         }
     }
+    if (const char *vendor = (const char *) glGetString(GL_VENDOR)) {
+        for (int i = 0; qglx_threadedgl_blacklist_vendor[i]; ++i) {
+            if (strstr(vendor, qglx_threadedgl_blacklist_vendor[i]) != 0) {
+                qCDebug(lcQpaGl).nospace() << "Multithreaded OpenGL disabled: "
+                                              "blacklisted vendor \""
+                                           << qglx_threadedgl_blacklist_vendor[i]
+                                           << "\"";
+                m_supportsThreading = false;
+                break;
+            }
+        }
+    }
 
     if (glxvendor && m_supportsThreading) {
         // Blacklist Mesa drivers due to QTCREATORBUG-10875 (crash in creator),
diff --git a/src/plugins/platforms/xcb/qxcbconnection.cpp b/src/plugins/platforms/xcb/qxcbconnection.cpp
index 1ff06dd39e..06d1000993 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection.cpp
@@ -152,10 +152,9 @@ QXcbConnection::~QXcbConnection()
     if (m_eventQueue)
         delete m_eventQueue;
 
-    QXcbIntegration *integration = QXcbIntegration::instance();
     // Delete screens in reverse order to avoid crash in case of multiple screens
     while (!m_screens.isEmpty())
-        integration->destroyScreen(m_screens.takeLast());
+        QWindowSystemInterface::handleScreenRemoved(m_screens.takeLast());
 
     while (!m_virtualDesktops.isEmpty())
         delete m_virtualDesktops.takeLast();
diff --git a/src/plugins/platforms/xcb/qxcbconnection_basic.h b/src/plugins/platforms/xcb/qxcbconnection_basic.h
index 3691763398..b979129cba 100644
--- a/src/plugins/platforms/xcb/qxcbconnection_basic.h
+++ b/src/plugins/platforms/xcb/qxcbconnection_basic.h
@@ -40,6 +40,7 @@
 #define QXCBBASICCONNECTION_H
 
 #include "qxcbatom.h"
+#include "qxcbexport.h"
 
 #include <QtCore/QPair>
 #include <QtCore/QObject>
@@ -55,7 +56,7 @@ QT_BEGIN_NAMESPACE
 
 Q_DECLARE_LOGGING_CATEGORY(lcQpaXcb)
 
-class QXcbBasicConnection : public QObject
+class Q_XCB_EXPORT QXcbBasicConnection : public QObject
 {
     Q_OBJECT
 public:
diff --git a/src/plugins/platforms/xcb/qxcbconnection_screens.cpp b/src/plugins/platforms/xcb/qxcbconnection_screens.cpp
index 4bafe83156..9ba71ada37 100644
--- a/src/plugins/platforms/xcb/qxcbconnection_screens.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection_screens.cpp
@@ -44,6 +44,8 @@
 #include <QtCore/QString>
 #include <QtCore/QList>
 
+#include <qpa/qwindowsysteminterface.h>
+
 #include <xcb/xinerama.h>
 
 void QXcbConnection::xrandrSelectEvents()
@@ -211,7 +213,7 @@ void QXcbConnection::updateScreen(QXcbScreen *screen, const xcb_randr_output_cha
                 m_screens.swapItemsAt(0, idx);
             }
             screen->virtualDesktop()->setPrimaryScreen(screen);
-            QXcbIntegration::instance()->setPrimaryScreen(screen);
+            QWindowSystemInterface::handlePrimaryScreenChanged(screen);
         }
     }
 }
@@ -234,7 +236,7 @@ QXcbScreen *QXcbConnection::createScreen(QXcbVirtualDesktop *virtualDesktop,
         m_screens.append(screen);
     }
     virtualDesktop->addScreen(screen);
-    QXcbIntegration::instance()->screenAdded(screen, screen->isPrimary());
+    QWindowSystemInterface::handleScreenAdded(screen, screen->isPrimary());
 
     return screen;
 }
@@ -261,10 +263,10 @@ void QXcbConnection::destroyScreen(QXcbScreen *screen)
             const int idx = m_screens.indexOf(newPrimary);
             if (idx > 0)
                 m_screens.swapItemsAt(0, idx);
-            QXcbIntegration::instance()->setPrimaryScreen(newPrimary);
+            QWindowSystemInterface::handlePrimaryScreenChanged(newPrimary);
         }
 
-        QXcbIntegration::instance()->destroyScreen(screen);
+        QWindowSystemInterface::handleScreenRemoved(screen);
     }
 }
 
@@ -406,7 +408,7 @@ void QXcbConnection::initializeScreens()
         // Push the screens to QGuiApplication
         for (QXcbScreen *screen : qAsConst(m_screens)) {
             qCDebug(lcQpaScreen) << "adding" << screen << "(Primary:" << screen->isPrimary() << ")";
-            QXcbIntegration::instance()->screenAdded(screen, screen->isPrimary());
+            QWindowSystemInterface::handleScreenAdded(screen, screen->isPrimary());
         }
 
         qCDebug(lcQpaScreen) << "primary output is" << qAsConst(m_screens).first()->name();
diff --git a/src/plugins/platforms/xcb/qxcbintegration.h b/src/plugins/platforms/xcb/qxcbintegration.h
index f13e232291..571726c354 100644
--- a/src/plugins/platforms/xcb/qxcbintegration.h
+++ b/src/plugins/platforms/xcb/qxcbintegration.h
@@ -137,8 +137,6 @@ private:
 
     QScopedPointer<QPlatformServices> m_services;
 
-    friend class QXcbConnection; // access QPlatformIntegration::screenAdded()
-
     mutable QByteArray m_wmClass;
     const char *m_instanceName;
     bool m_canGrab;
diff --git a/src/plugins/platforms/xcb/qxcbnativeinterface.cpp b/src/plugins/platforms/xcb/qxcbnativeinterface.cpp
index 4d526a6bda..899081e752 100644
--- a/src/plugins/platforms/xcb/qxcbnativeinterface.cpp
+++ b/src/plugins/platforms/xcb/qxcbnativeinterface.cpp
@@ -412,12 +412,15 @@ void *QXcbNativeInterface::atspiBus()
         auto reply = Q_XCB_REPLY(xcb_get_property, defaultConnection->xcb_connection(),
                                      false, defaultConnection->rootWindow(),
                                      atspiBusAtom, XCB_ATOM_STRING, 0, 128);
-        Q_ASSERT(!reply->bytes_after);
+        if (!reply)
+            return nullptr;
+
         char *data = (char *)xcb_get_property_value(reply.get());
         int length = xcb_get_property_value_length(reply.get());
         return new QByteArray(data, length);
     }
-    return 0;
+
+    return nullptr;
 }
 
 void QXcbNativeInterface::setAppTime(QScreen* screen, xcb_timestamp_t time)
diff --git a/src/tools/androiddeployqt/main.cpp b/src/tools/androiddeployqt/main.cpp
index fd7f72eebf..3af5237f3d 100644
--- a/src/tools/androiddeployqt/main.cpp
+++ b/src/tools/androiddeployqt/main.cpp
@@ -900,7 +900,7 @@ bool readInputFile(Options *options)
             options->extraPlugins = extraPlugins.toString().split(QLatin1Char(','));
     }
 
-    {
+    if (!options->auxMode) {
         const QJsonValue stdcppPath = jsonObject.value(QStringLiteral("stdcpp-path"));
         if (stdcppPath.isUndefined()) {
             fprintf(stderr, "No stdcpp-path defined in json file.\n");
diff --git a/src/widgets/kernel/qgesturemanager.cpp b/src/widgets/kernel/qgesturemanager.cpp
index 57d6994c88..cd27c9c5be 100644
--- a/src/widgets/kernel/qgesturemanager.cpp
+++ b/src/widgets/kernel/qgesturemanager.cpp
@@ -143,11 +143,6 @@ Qt::GestureType QGestureManager::registerGestureRecognizer(QGestureRecognizer *r
 void QGestureManager::unregisterGestureRecognizer(Qt::GestureType type)
 {
     QList<QGestureRecognizer *> list = m_recognizers.values(type);
-    while (QGestureRecognizer *recognizer = m_recognizers.take(type)) {
-        // ensuring an entry exists causes the recognizer to be deleted on destruction of the manager
-        auto &gestures = m_obsoleteGestures[recognizer];
-        Q_UNUSED(gestures);
-    }
     foreach (QGesture *g, m_gestureToRecognizer.keys()) {
         QGestureRecognizer *recognizer = m_gestureToRecognizer.value(g);
         if (list.contains(recognizer)) {
diff --git a/src/widgets/kernel/qgesturerecognizer.cpp b/src/widgets/kernel/qgesturerecognizer.cpp
index 65c46a5e56..75d091ce4e 100644
--- a/src/widgets/kernel/qgesturerecognizer.cpp
+++ b/src/widgets/kernel/qgesturerecognizer.cpp
@@ -41,6 +41,7 @@
 
 #include "private/qgesture_p.h"
 #include "private/qgesturemanager_p.h"
+#include "private/qapplication_p.h"
 
 #ifndef QT_NO_GESTURES
 
@@ -231,6 +232,11 @@ Qt::GestureType QGestureRecognizer::registerRecognizer(QGestureRecognizer *recog
 */
 void QGestureRecognizer::unregisterRecognizer(Qt::GestureType type)
 {
+    auto qAppPriv = QApplicationPrivate::instance();
+    if (!qAppPriv)
+        return;
+    if (!qAppPriv->gestureManager)
+        return;
     QGestureManager::instance()->unregisterGestureRecognizer(type);
 }
 
diff --git a/src/widgets/styles/qstyle.cpp b/src/widgets/styles/qstyle.cpp
index ac4fb7fbd1..97ec1d3f19 100644
--- a/src/widgets/styles/qstyle.cpp
+++ b/src/widgets/styles/qstyle.cpp
@@ -1971,8 +1971,8 @@ void QStyle::drawItemPixmap(QPainter *painter, const QRect &rect, int alignment,
 
     \value SH_Widget_Animate Deprecated. Use \l{SH_Widget_Animation_Duration} instead.
 
-    \value SH_Splitter_OpaqueResize Determines if resizing is opaque
-           This enum value has been introduced in Qt 5.2
+    \value SH_Splitter_OpaqueResize Determines if widgets are resized dynamically (opaquely) while
+           interactively moving the splitter. This enum value was introduced in Qt 5.2.
 
     \value SH_TabBar_ChangeCurrentDelay Determines the delay before the current
            tab is changed while dragging over the tabbar, in milliseconds. This
diff --git a/src/widgets/widgets/qsplashscreen.cpp b/src/widgets/widgets/qsplashscreen.cpp
index 4af4f90119..bf6bf1c7c9 100644
--- a/src/widgets/widgets/qsplashscreen.cpp
+++ b/src/widgets/widgets/qsplashscreen.cpp
@@ -289,8 +289,7 @@ void QSplashScreen::setPixmap(const QPixmap &pixmap)
 // 1) If a QDesktopScreenWidget is found in the parent hierarchy, use that (see docs on
 //    QSplashScreen(QWidget *, QPixmap).
 // 2) If a widget with associated QWindow is found, use that
-// 3) When nothing can be found, do not position the widget, allowing for
-//    QPlatformWindow::initialGeometry() to center it over the cursor
+// 3) When nothing can be found, try to center it over the cursor
 
 static inline int screenNumberOf(const QDesktopScreenWidget *dsw)
 {
@@ -307,7 +306,15 @@ const QScreen *QSplashScreenPrivate::screenFor(const QWidget *w)
         if (QWindow *window = p->windowHandle())
             return window->screen();
     }
-    return nullptr;
+#if QT_CONFIG(cursor)
+    // Note: We could rely on QPlatformWindow::initialGeometry() to center it
+    // over the cursor, but not all platforms (namely Android) use that.
+    if (QGuiApplication::screens().size() > 1) {
+        if (auto screenAtCursor = QGuiApplication::screenAt(QCursor::pos()))
+            return screenAtCursor;
+    }
+#endif // cursor
+    return QGuiApplication::primaryScreen();
 }
 
 void QSplashScreenPrivate::setPixmap(const QPixmap &p, const QScreen *screen)
diff --git a/src/widgets/widgets/qsplitter.cpp b/src/widgets/widgets/qsplitter.cpp
index 98bb23caad..de838a8f93 100644
--- a/src/widgets/widgets/qsplitter.cpp
+++ b/src/widgets/widgets/qsplitter.cpp
@@ -161,11 +161,10 @@ Qt::Orientation QSplitterHandle::orientation() const
 
 
 /*!
-    Returns \c true if widgets are resized dynamically (opaquely), otherwise
-    returns \c false. This value is controlled by the QSplitter.
+    Returns \c true if widgets are resized dynamically (opaquely) while interactively moving the
+    splitter. Otherwise returns \c false. This value is controlled by the QSplitter.
 
     \sa QSplitter::opaqueResize()
-
 */
 bool QSplitterHandle::opaqueResize() const
 {
@@ -1483,7 +1482,8 @@ int QSplitter::closestLegalPosition(int pos, int index)
 
 /*!
     \property QSplitter::opaqueResize
-    \brief whether resizing is opaque
+    Returns \c true if widgets are resized dynamically (opaquely) while interactively moving the
+    splitter. Otherwise returns \c false.
 
     The default resize behavior is style dependent (determined by the
     SH_Splitter_OpaqueResize style hint). However, you can override it