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
Pick-to: 6.5 6.4
Change-Id: I7172e27bfef86d82cd51de70b40de42e8895bae6
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 73 insertions, 0 deletions

diff --git a/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp b/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp
index 0b495b2379..7e7cc8da7c 100644
--- a/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp
+++ b/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