Add convenience function for checking screen changes to QPlatformWindow.

Add function returning the screen for a new geometry for geometry
change events. This ensures that the checking is done in platform
screen coordinates (which might differ from QScreen coordinates
due to high-DPI changes) and also that no screen changes are
emitted for child windows.

Change-Id: I406750f59f006f834c386d09c0c85a804014924a
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>

4 files changed, 31 insertions, 33 deletions

diff --git a/src/gui/kernel/qplatformwindow.cpp b/src/gui/kernel/qplatformwindow.cpp
index faaf418522..bb7b690992 100644
--- a/src/gui/kernel/qplatformwindow.cpp
+++ b/src/gui/kernel/qplatformwindow.cpp
@@ -474,6 +474,29 @@ QString QPlatformWindow::formatWindowTitle(const QString &title, const QString &
 }
 
 /*!
+    Helper function for finding the new screen for \a newGeometry in response to
+    a geometry changed event. Returns the new screen if the window was moved to
+    another virtual sibling. If the screen changes, the platform plugin should call
+    QWindowSystemInterface::handleWindowScreenChanged().
+    \note: The current screen will always be returned for child windows since
+    they should never signal screen changes.
+
+    \since 5.4
+    \sa QWindowSystemInterface::handleWindowScreenChanged()
+*/
+QPlatformScreen *QPlatformWindow::screenForGeometry(const QRect &newGeometry) const
+{
+    QPlatformScreen *currentScreen = screen();
+    if (!parent() && !currentScreen->geometry().intersects(newGeometry)) {
+        Q_FOREACH (QPlatformScreen* screen, currentScreen->virtualSiblings()) {
+            if (screen->geometry().intersects(newGeometry))
+                return screen;
+        }
+    }
+    return currentScreen;
+}
+
+/*!
     Reimplement this method to set whether the window demands attention
     (for example, by flashing the taskbar icon) depending on \a enabled.
 
diff --git a/src/gui/kernel/qplatformwindow.h b/src/gui/kernel/qplatformwindow.h
index 39bd8324a0..8f0e5ff352 100644
--- a/src/gui/kernel/qplatformwindow.h
+++ b/src/gui/kernel/qplatformwindow.h
@@ -139,6 +139,7 @@ public:
 
 protected:
     static QString formatWindowTitle(const QString &title, const QString &separator);
+    QPlatformScreen *screenForGeometry(const QRect &newGeometry) const;
 
     QScopedPointer<QPlatformWindowPrivate> d_ptr;
 private:
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 7d0b00b312..51497b3300 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -1376,25 +1376,6 @@ void QWindowsWindow::handleResized(int wParam)
     }
 }
 
-// Return the effective screen for full screen mode in a virtual desktop.
-static QScreen *effectiveScreen(const QWindow *w)
-{
-    QRect geometry = w->geometry();
-    if (!w->isTopLevel())
-        geometry.moveTopLeft(w->mapToGlobal(geometry.topLeft()));
-
-    QScreen *screen = w->screen();
-    if (!screen->geometry().intersects(geometry)) {
-        foreach (QScreen *sibling, screen->virtualSiblings()) {
-            if (sibling->geometry().intersects(geometry)) {
-                screen = sibling;
-                break;
-            }
-        }
-    }
-    return screen;
-}
-
 void QWindowsWindow::handleGeometryChange()
 {
     //Prevent recursive resizes for Windows CE
@@ -1411,12 +1392,9 @@ void QWindowsWindow::handleGeometryChange()
         fireExpose(QRegion(m_data.geometry), true);
     }
     if (previousGeometry.topLeft() != m_data.geometry.topLeft()) {
-        QWindow *w = window();
-        if (w->isTopLevel()) {
-            QScreen *newScreen = effectiveScreen(w);
-            if (newScreen != w->screen())
-                QWindowSystemInterface::handleWindowScreenChanged(w, newScreen);
-        }
+        QPlatformScreen *newScreen = screenForGeometry(m_data.geometry);
+        if (newScreen != screen())
+            QWindowSystemInterface::handleWindowScreenChanged(window(), newScreen->screen());
     }
     if (testFlag(SynchronousGeometryChangeEvent))
         QWindowSystemInterface::flushWindowSystemEvents();
diff --git a/src/plugins/platforms/xcb/qxcbwindow.cpp b/src/plugins/platforms/xcb/qxcbwindow.cpp
index 0cc8c8dbfe..578b4d6ec1 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.cpp
+++ b/src/plugins/platforms/xcb/qxcbwindow.cpp
@@ -1842,14 +1842,10 @@ void QXcbWindow::handleConfigureNotifyEvent(const xcb_configure_notify_event_t *
     QPlatformWindow::setGeometry(rect);
     QWindowSystemInterface::handleGeometryChange(window(), rect);
 
-    if (!m_screen->availableGeometry().intersects(rect)) {
-        Q_FOREACH (QPlatformScreen* screen, m_screen->virtualSiblings()) {
-            if (screen->availableGeometry().intersects(rect)) {
-                m_screen = static_cast<QXcbScreen*>(screen);
-                QWindowSystemInterface::handleWindowScreenChanged(window(), m_screen->QPlatformScreen::screen());
-                break;
-            }
-        }
+    QPlatformScreen *newScreen = screenForGeometry(rect);
+    if (newScreen != m_screen) {
+        m_screen = static_cast<QXcbScreen*>(newScreen);
+        QWindowSystemInterface::handleWindowScreenChanged(window(), newScreen->screen());
     }
 
     m_configureNotifyPending = false;