Windows: Restore maximized/full screen widgets to correct screen.

Partially revert 54865d47cfd859a0e84ba8e1bbff3b56c93d4e0d and
bring back parts from abba37cd0eff959edf2d011842cbf2b36cce8467 which
failed some tests on other platforms and never made it in.

Avoid setting a geometry on maximized windows since that leaves
them in a broken state. Instead, if there is a need to restore
maximized windows to a different screen, clear the maximized flag
before applying the geometry.

[ChangeLog][QWidget][Windows] QWidget::restoreGeometry() now restores
maximized/full screen widgets to the correct screen.

Task-number: QTBUG-21371
Task-number: QTBUG-4397

Change-Id: Ibd5b736e921f20d4b7365c06c6f9c5dd4469c781
Reviewed-by: Andy Shaw <andy.shaw@digia.com>
(cherry picked from qtbase/ae4243df1e53b0aaeada708f6fa7979a0f0d216a)

1 files changed, 17 insertions, 4 deletions

diff --git a/src/gui/kernel/qwidget.cpp b/src/gui/kernel/qwidget.cpp
index 53c1d3f64d..de7a4a1852 100644
--- a/src/gui/kernel/qwidget.cpp
+++ b/src/gui/kernel/qwidget.cpp
@@ -7139,12 +7139,25 @@ bool QWidget::restoreGeometry(const QByteArray &geometry)
     if (maximized || fullScreen) {
         // set geomerty before setting the window state to make
         // sure the window is maximized to the right screen.
-        // Skip on windows: the window is restored into a broken
-        // half-maximized state.
+        Qt::WindowStates ws = windowState();
 #ifndef Q_WS_WIN
         setGeometry(restoredNormalGeometry);
-#endif
-        Qt::WindowStates ws = windowState();
+#else
+        if (ws & Qt::WindowFullScreen) {
+            // Full screen is not a real window state on Windows.
+            move(availableGeometry.topLeft());
+        } else if (ws & Qt::WindowMaximized) {
+            // Setting a geometry on an already maximized window causes this to be
+            // restored into a broken, half-maximized state, non-resizable state (QTBUG-4397).
+            // Move the window in normal state if needed.
+            if (restoredScreenNumber != desktop->screenNumber(this)) {
+                setWindowState(Qt::WindowNoState);
+                setGeometry(restoredNormalGeometry);
+            }
+        } else {
+            setGeometry(restoredNormalGeometry);
+        }
+#endif // Q_WS_WIN
         if (maximized)
             ws |= Qt::WindowMaximized;
         if (fullScreen)