QWidget::save/restoreGeometry(): Check screen size.

Bump minor version of the saved geometry and append
the screen width in version 1.1. Use that to check and bail out should
large differences occur due to scaling or different levels of DPI
awareness.

Task-number: QTBUG-38858
Change-Id: Iad8ae0705297118b4237c9a41469cb97d7eab549
Reviewed-by: Alessandro Portale <alessandro.portale@digia.com>

1 files changed, 27 insertions, 4 deletions

diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index 8ea43cfb6c..34adea866e 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/src/widgets/kernel/qwidget.cpp
@@ -7203,8 +7203,12 @@ QByteArray QWidget::saveGeometry() const
     QDataStream stream(&array, QIODevice::WriteOnly);
     stream.setVersion(QDataStream::Qt_4_0);
     const quint32 magicNumber = 0x1D9D0CB;
+    // Version history:
+    // - Qt 4.2 - 4.8.6, 5.0 - 5.3    : Version 1.0
+    // - Qt 4.8.6 - today, 5.4 - today: Version 1.1, save screen width in addition to check for high DPI scaling.
     quint16 majorVersion = 1;
-    quint16 minorVersion = 0;
+    quint16 minorVersion = 1;
+    const int screenNumber = QApplication::desktop()->screenNumber(this);
     stream << magicNumber
            << majorVersion
            << minorVersion
@@ -7215,9 +7219,10 @@ QByteArray QWidget::saveGeometry() const
            << frameGeometry()
            << normalGeometry()
 #endif // Q_WS_MAC
-           << qint32(QApplication::desktop()->screenNumber(this))
+           << qint32(screenNumber)
            << quint8(windowState() & Qt::WindowMaximized)
-           << quint8(windowState() & Qt::WindowFullScreen);
+           << quint8(windowState() & Qt::WindowFullScreen)
+           << qint32(QApplication::desktop()->screenGeometry(screenNumber).width()); // 1.1 onwards
     return array;
 }
 
@@ -7272,6 +7277,7 @@ bool QWidget::restoreGeometry(const QByteArray &geometry)
     qint32 restoredScreenNumber;
     quint8 maximized;
     quint8 fullScreen;
+    qint32 restoredScreenWidth = 0;
 
     stream >> restoredFrameGeometry
            >> restoredNormalGeometry
@@ -7279,6 +7285,24 @@ bool QWidget::restoreGeometry(const QByteArray &geometry)
            >> maximized
            >> fullScreen;
 
+    if (majorVersion > 1 || minorVersion >= 1)
+        stream >> restoredScreenWidth;
+
+    const QDesktopWidget * const desktop = QApplication::desktop();
+    const qreal screenWidthF = qreal(desktop->screenGeometry(restoredScreenNumber).width());
+    // Sanity check bailing out when large variations of screen sizes occur due to
+    // high DPI scaling or different levels of DPI awareness.
+    if (restoredScreenWidth) {
+        const qreal factor = qreal(restoredScreenWidth) / screenWidthF;
+        if (factor < 0.8 || factor > 1.25)
+            return false;
+    } else {
+        // Saved by Qt 5.3 and earlier, try to prevent too large windows
+        // unless the size will be adapted by maximized or fullscreen.
+        if (!maximized && !fullScreen && qreal(restoredFrameGeometry.width()) / screenWidthF > 1.5)
+            return false;
+    }
+
     const int frameHeight = 20;
     if (!restoredFrameGeometry.isValid())
         restoredFrameGeometry = QRect(QPoint(0,0), sizeHint());
@@ -7292,7 +7316,6 @@ bool QWidget::restoreGeometry(const QByteArray &geometry)
                                        .expandedTo(d_func()->adjustedSize()));
     }
 
-    const QDesktopWidget * const desktop = QApplication::desktop();
     if (restoredScreenNumber >= desktop->numScreens())
         restoredScreenNumber = desktop->primaryScreen();