Fix QWidget::restoreGeometry when restored geometry is off screen

If a widget's geometry is restored to a screen, which is smaller than
the one it was saved from,
- the widget could appear (partly) off screen
- the widget's title bar and resize handles could be inaccessible

This patch refactors and documents checkRestoredGeometry.
In a first step, the restored geometry's size is checked against
a given screen size. It is corrected if necessary.
In a second step, the restored geometry is moved inside the screen,
if necessary.
It makes the function a static member of QWidgetPrivate in order to
expose it for auto testing and adds a respective test function to
tst_QWidget.

Fixes: QTBUG-77385
Fixes: QTBUG-4397
Task-number: QTBUG-69104
Change-Id: I7172e27bfef86d82cd51de70b40de42e8895bae6
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
(cherry picked from commit 5edb71c6d4cb0051d27d023ddcd180c5f59f2725)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/kernel/qwidget.cpp

@@ -7382,15 +7382,65 @@ QByteArray QWidget::saveGeometry() const
     return array;
 }
 
-static void checkRestoredGeometry(const QRect &availableGeometry, QRect *restoredGeometry,
+/*!
+   \internal Check a if \a restoredGeometry fits into \a availableGeometry
+   This method is used to verify that a widget is restored to a geometry, which
+   fits into the target screen.
+
+   \param frameHeight represents the height of the widget's title bar, which is expected
+   to be on its top.
+
+   If the size of \a restoredGeometry exceeds \a availableGeometry, its height and width
+   will be resized to be two pixels smaller than \a availableGeometry. An exact match would
+   be full screen.
+
+   If at least one edge of \a restoredGeometry is outside \a availableGeometry,
+   \a restoredGeometry will be moved
+   \list
+   \li down if its top is off screen
+   \li up if its bottom is off screen
+   \li right if its left edge is off screen
+   \li left if its right edge is off screen
+   \endlist
+ */
+void QWidgetPrivate::checkRestoredGeometry(const QRect &availableGeometry, QRect *restoredGeometry,
                                   int frameHeight)
 {
-    if (!restoredGeometry->intersects(availableGeometry)) {
-        restoredGeometry->moveBottom(qMin(restoredGeometry->bottom(), availableGeometry.bottom()));
-        restoredGeometry->moveLeft(qMax(restoredGeometry->left(), availableGeometry.left()));
-        restoredGeometry->moveRight(qMin(restoredGeometry->right(), availableGeometry.right()));
+    // compare with restored geometry's height increased by frameHeight
+    const int height = restoredGeometry->height() + frameHeight;
+
+    // Step 1: Resize if necessary:
+    // make height / width 2px smaller than screen, because an exact match would be fullscreen
+    if (availableGeometry.height() <= height)
+        restoredGeometry->setHeight(availableGeometry.height() - 2 - frameHeight);
+    if (availableGeometry.width() <= restoredGeometry->width())
+        restoredGeometry->setWidth(availableGeometry.width() - 2);
+
+    // Step 2: Move if necessary:
+    // Construct a rectangle from restored Geometry adjusted by frameHeight
+    const QRect restored = restoredGeometry->adjusted(0, -frameHeight, 0, 0);
+
+    // Return if restoredGeometry (including frame) fits into screen
+    if (availableGeometry.contains(restored))
+        return;
+
+    // (size is correct, but at least one edge is off screen)
+
+    // Top out of bounds => move down
+    if (restored.top() <= availableGeometry.top()) {
+        restoredGeometry->moveTop(availableGeometry.top() + 1 + frameHeight);
+    } else if (restored.bottom() >= availableGeometry.bottom()) {
+        // Bottom out of bounds => move up
+        restoredGeometry->moveBottom(availableGeometry.bottom() - 1);
+    }
+
+    // Left edge out of bounds => move right
+    if (restored.left() <= availableGeometry.left()) {
+        restoredGeometry->moveLeft(availableGeometry.left() + 1);
+    } else if (restored.right() >= availableGeometry.right()) {
+        // Right edge out of bounds => move left
+        restoredGeometry->moveRight(availableGeometry.right() - 1);
     }
-    restoredGeometry->moveTop(qMax(restoredGeometry->top(), availableGeometry.top() + frameHeight));
 }
 
 /*!
@@ -7477,7 +7527,9 @@ bool QWidget::restoreGeometry(const QByteArray &geometry)
             return false;
     }
 
-    const int frameHeight = 20;
+    const int frameHeight = QApplication::style()
+                          ? QApplication::style()->pixelMetric(QStyle::PM_TitleBarHeight)
+                          : 20;
 
     if (!restoredNormalGeometry.isValid())
         restoredNormalGeometry = QRect(QPoint(0, frameHeight), sizeHint());
@@ -7493,11 +7545,11 @@ bool QWidget::restoreGeometry(const QByteArray &geometry)
 
     // Modify the restored geometry if we are about to restore to coordinates
     // that would make the window "lost". This happens if:
-    // - The restored geometry is completely oustside the available geometry
+    // - The restored geometry is completely or partly oustside the available geometry
     // - The title bar is outside the available geometry.
 
-    checkRestoredGeometry(availableGeometry, &restoredGeometry, frameHeight);
-    checkRestoredGeometry(availableGeometry, &restoredNormalGeometry, frameHeight);
+    QWidgetPrivate::checkRestoredGeometry(availableGeometry, &restoredGeometry, frameHeight);
+    QWidgetPrivate::checkRestoredGeometry(availableGeometry, &restoredNormalGeometry, frameHeight);
 
     if (maximized || fullScreen) {
         // set geometry before setting the window state to make
@@ -7529,6 +7581,8 @@ bool QWidget::restoreGeometry(const QByteArray &geometry)
        d_func()->topData()->normalGeometry = restoredNormalGeometry;
     } else {
         setWindowState(windowState() & ~(Qt::WindowMaximized | Qt::WindowFullScreen));
+
+        // FIXME: Why fall back to restoredNormalGeometry if majorVersion <= 2?
         if (majorVersion > 2)
             setGeometry(restoredGeometry);
         else

src/widgets/kernel/qwidget_p.h

@@ -210,6 +210,9 @@ public:
     static QWidgetPrivate *get(QWidget *w) { return w->d_func(); }
     static const QWidgetPrivate *get(const QWidget *w) { return w->d_func(); }
 
+    static void checkRestoredGeometry(const QRect &availableGeometry, QRect *restoredGeometry,
+                                      int frameHeight);
+
     QWExtra *extraData() const;
     QTLWExtra *topData() const;
     QTLWExtra *maybeTopData() const;

tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp

@@ -195,6 +195,8 @@ private slots:
     void saveRestoreGeometry();
     void restoreVersion1Geometry_data();
     void restoreVersion1Geometry();
+    void restoreGeometryAfterScreenChange_data();
+    void restoreGeometryAfterScreenChange();
 
     void widgetAt();
 #ifdef Q_OS_MACOS
@@ -434,6 +436,15 @@ private:
     QPointingDevice *m_touchScreen;
     const int m_fuzz;
     QPalette simplePalette();
+
+private:
+    enum class ScreenPosition {
+        OffAbove,
+        OffLeft,
+        OffBelow,
+        OffRight,
+        Contained
+    };
 };
 
 // Testing get/set functions
@@ -4245,6 +4256,68 @@ void tst_QWidget::restoreVersion1Geometry()
 #endif
 }
 
+void tst_QWidget::restoreGeometryAfterScreenChange_data()
+{
+    QTest::addColumn<ScreenPosition>("screenPosition");
+    QTest::addColumn<int>("deltaWidth");
+    QTest::addColumn<int>("deltaHeight");
+    QTest::addColumn<int>("frameMargin");
+    QTest::addColumn<bool>("outside");
+
+    QTest::newRow("offAboveLarge") << ScreenPosition::OffAbove << 200 << 250 << 20 << true;
+    QTest::newRow("fitting") << ScreenPosition::Contained << 80 << 80 << 20 << false;
+    QTest::newRow("offRightWide") << ScreenPosition::OffRight << 150 << 80 << 20 << false;
+    QTest::newRow("offLeftFitting") << ScreenPosition::OffLeft << 70 << 70 << 20 << true;
+    QTest::newRow("offBelowHigh") << ScreenPosition::OffBelow << 80 << 200 << 20 << false;
+}
+
+void tst_QWidget::restoreGeometryAfterScreenChange()
+{
+    const QList<QScreen *> &screens = QApplication::screens();
+    QVERIFY2(!screens.isEmpty(), "No screens found.");
+    const QRect screenGeometry = screens.at(0)->geometry();
+
+    QFETCH(ScreenPosition, screenPosition);
+    QFETCH(int, deltaWidth);
+    QFETCH(int, deltaHeight);
+    QFETCH(int, frameMargin);
+    QFETCH(bool, outside);
+
+    QRect restoredGeometry = screenGeometry;
+    restoredGeometry.setHeight(screenGeometry.height() * deltaHeight / 100);
+    restoredGeometry.setWidth(screenGeometry.width() * deltaWidth / 100);
+    const float moveMargin = outside ? 1.2 : 0.75;
+
+    switch (screenPosition) {
+    case ScreenPosition::OffLeft:
+        restoredGeometry.setLeft(restoredGeometry.width() * (-moveMargin));
+        break;
+    case ScreenPosition::OffAbove:
+        restoredGeometry.setTop(restoredGeometry.height() * (-moveMargin));
+        break;
+    case ScreenPosition::OffRight:
+        restoredGeometry.setRight(restoredGeometry.width() * moveMargin);
+        break;
+    case ScreenPosition::OffBelow:
+        restoredGeometry.setBottom(restoredGeometry.height() * moveMargin);
+        break;
+    case ScreenPosition::Contained:
+        break;
+    }
+
+    // If restored geometry fits into screen and has not been moved,
+    // it is changed only by frame margin plus one pixel at each edge
+    const QRect originalGeometry = restoredGeometry.adjusted(1, frameMargin + 1, 1, frameMargin + 1);
+
+    QWidgetPrivate::checkRestoredGeometry(screenGeometry, &restoredGeometry, frameMargin);
+
+    if (deltaHeight < 100 && deltaWidth < 100 && screenPosition == ScreenPosition::Contained)
+        QCOMPARE(originalGeometry, restoredGeometry);
+
+    // new geometry has to fit on the screen
+    QVERIFY(screenGeometry.contains(restoredGeometry));
+}
+
 void tst_QWidget::widgetAt()
 {
 #ifdef Q_OS_MACOS