Add QPlatformScreen::windows() helper to return all windows on screen

Change-Id: Ib55b37b64ed0890ca777dfea8c4d702e267c34bf
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>

src/gui/kernel/qplatformscreen.cpp

@@ -103,6 +103,20 @@ QWindow *QPlatformScreen::topLevelAt(const QPoint & pos) const
     return 0;
 }
 
+/*!
+    Return all windows residing on this screen.
+*/
+QWindowList QPlatformScreen::windows() const
+{
+    QWindowList windows;
+    for (QWindow *window : QGuiApplication::allWindows()) {
+        if (platformScreenForWindow(window) != this)
+            continue;
+        windows.append(window);
+    }
+    return windows;
+}
+
 /*!
   Find the sibling screen corresponding to \a globalPos.
 
@@ -369,25 +383,17 @@ QPlatformCursor *QPlatformScreen::cursor() const
 */
 void QPlatformScreen::resizeMaximizedWindows()
 {
-    QList<QWindow*> windows = QGuiApplication::allWindows();
-
     // 'screen()' still has the old geometry info while 'this' has the new geometry info
     const QRect oldGeometry = screen()->geometry();
     const QRect oldAvailableGeometry = screen()->availableGeometry();
     const QRect newGeometry = deviceIndependentGeometry();
     const QRect newAvailableGeometry = QHighDpi::fromNative(availableGeometry(), QHighDpiScaling::factor(this), newGeometry.topLeft());
 
-    // make sure maximized and fullscreen windows are updated
-    for (int i = 0; i < windows.size(); ++i) {
-        QWindow *w = windows.at(i);
-
+    for (QWindow *w : windows()) {
         // Skip non-platform windows, e.g., offscreen windows.
         if (!w->handle())
             continue;
 
-        if (platformScreenForWindow(w) != this)
-            continue;
-
         if (w->windowState() & Qt::WindowMaximized || w->geometry() == oldAvailableGeometry)
             w->setGeometry(newAvailableGeometry);
         else if (w->windowState() & Qt::WindowFullScreen || w->geometry() == oldGeometry)

src/gui/kernel/qplatformscreen.h

@@ -123,6 +123,8 @@ public:
     virtual void setOrientationUpdateMask(Qt::ScreenOrientations mask);
 
     virtual QWindow *topLevelAt(const QPoint &point) const;
+    QWindowList windows() const;
+
     virtual QList<QPlatformScreen *> virtualSiblings() const;
     const QPlatformScreen *screenForPosition(const QPoint &point) const;