Windows QPA: Fix wrong scaling of fixed size in window creation phase

When a fixed size the window is moved to another screen
by QPlatformWindow::initialGeometry(), the size constraints
would be incorrectly scaled using the initial screen in the handling of
WM_GETMINMAXINFO.
To fix this, pass the resulting screen out of QPlatformWindow::initialGeometry()
and use it during the window creation phase.

Fixes: QTBUG-77307
Change-Id: I149a2a65e816da841a32abc14a495925bf9cc6f6
Reviewed-by: André de la Rocha <andre.rocha@qt.io>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

src/gui/kernel/qplatformwindow.cpp

@@ -694,9 +694,12 @@ static QSize fixInitialSize(QSize size, const QWindow *w,
     However if the given window already has geometry which the application has
     initialized, it takes priority.
 */
-QRect QPlatformWindow::initialGeometry(const QWindow *w,
+QRect QPlatformWindow::initialGeometry(const QWindow *w, const QRect &initialGeometry,
-    const QRect &initialGeometry, int defaultWidth, int defaultHeight)
+                                       int defaultWidth, int defaultHeight,
+                                       const QScreen **resultingScreenReturn)
 {
+    if (resultingScreenReturn)
+        *resultingScreenReturn = w->screen();
     if (!w->isTopLevel()) {
         const qreal factor = QHighDpiScaling::factor(w);
         const QSize size = fixInitialSize(QHighDpi::fromNative(initialGeometry.size(), factor),
@@ -712,6 +715,8 @@ QRect QPlatformWindow::initialGeometry(const QWindow *w,
         : QGuiApplication::screenAt(initialGeometry.center());
     if (!screen)
         return initialGeometry;
+    if (resultingScreenReturn)
+        *resultingScreenReturn = screen;
     // initialGeometry refers to window's screen
     QRect rect(QHighDpi::fromNativePixels(initialGeometry, w));
     if (wp->resizeAutomatic)

src/gui/kernel/qplatformwindow.h

@@ -63,6 +63,7 @@ QT_BEGIN_NAMESPACE
 
 class QPlatformScreen;
 class QPlatformWindowPrivate;
+class QScreen;
 class QWindow;
 class QIcon;
 class QRegion;
@@ -142,8 +143,9 @@ public:
 
     virtual void invalidateSurface();
 
-    static QRect initialGeometry(const QWindow *w,
+    static QRect initialGeometry(const QWindow *w, const QRect &initialGeometry,
-        const QRect &initialGeometry, int defaultWidth, int defaultHeight);
+                                 int defaultWidth, int defaultHeight,
+                                 const QScreen **resultingScreenReturn = nullptr);
 
     virtual void requestUpdate();
     bool hasPendingUpdateRequest() const;

src/plugins/platforms/windows/qwindowswindow.cpp

@@ -759,7 +759,10 @@ QWindowsWindowData
 
     const QString windowClassName = QWindowsContext::instance()->registerWindowClass(w);
 
-    const QRect rect = QPlatformWindow::initialGeometry(w, data.geometry, defaultWindowWidth, defaultWindowHeight);
+    const QScreen *screen{};
+    const QRect rect = QPlatformWindow::initialGeometry(w, data.geometry,
+                                                        defaultWindowWidth, defaultWindowHeight,
+                                                        &screen);
 
     if (title.isEmpty() && (result.flags & Qt::WindowTitleHint))
         title = topLevel ? qAppName() : w->objectName();
@@ -769,7 +772,9 @@ QWindowsWindowData
 
     // Capture events before CreateWindowEx() returns. The context is cleared in
     // the QWindowsWindow constructor.
-    const QWindowCreationContextPtr context(new QWindowCreationContext(w, data.geometry, rect, data.customMargins, style, exStyle));
+    const QWindowCreationContextPtr context(new QWindowCreationContext(w, screen, data.geometry,
+                                                                       rect, data.customMargins,
+                                                                       style, exStyle));
     QWindowsContext::instance()->setWindowCreationContext(context);
 
     const bool hasFrame = (style & (WS_DLGFRAME | WS_THICKFRAME));
@@ -879,10 +884,10 @@ void WindowCreationData::initialize(const QWindow *w, HWND hwnd, bool frameChang
 
 
 // Scaling helpers for size constraints.
-static QSize toNativeSizeConstrained(QSize dip, const QWindow *w)
+static QSize toNativeSizeConstrained(QSize dip, const QScreen *s)
 {
     if (QHighDpiScaling::isActive()) {
-        const qreal factor = QHighDpiScaling::factor(w);
+        const qreal factor = QHighDpiScaling::factor(s);
         if (!qFuzzyCompare(factor, qreal(1))) {
             if (dip.width() > 0 && dip.width() < QWINDOWSIZE_MAX)
                 dip.setWidth(qRound(qreal(dip.width()) * factor));
@@ -995,11 +1000,12 @@ bool QWindowsGeometryHint::handleCalculateSize(const QMargins &customMargins, co
     return true;
 }
 
-void QWindowsGeometryHint::frameSizeConstraints(const QWindow *w, const QMargins &margins,
+void QWindowsGeometryHint::frameSizeConstraints(const QWindow *w, const QScreen *screen,
+                                                const QMargins &margins,
                                                 QSize *minimumSize, QSize *maximumSize)
 {
-    *minimumSize = toNativeSizeConstrained(w->minimumSize(), w);
+    *minimumSize = toNativeSizeConstrained(w->minimumSize(), screen);
-    *maximumSize = toNativeSizeConstrained(w->maximumSize(), w);
+    *maximumSize = toNativeSizeConstrained(w->maximumSize(), screen);
 
     const int maximumWidth = qMax(maximumSize->width(), minimumSize->width());
     const int maximumHeight = qMax(maximumSize->height(), minimumSize->height());
@@ -1017,12 +1023,13 @@ void QWindowsGeometryHint::frameSizeConstraints(const QWindow *w, const QMargins
 }
 
 void QWindowsGeometryHint::applyToMinMaxInfo(const QWindow *w,
+                                             const QScreen *screen,
                                              const QMargins &margins,
                                              MINMAXINFO *mmi)
 {
     QSize minimumSize;
     QSize maximumSize;
-    frameSizeConstraints(w, margins, &minimumSize, &maximumSize);
+    frameSizeConstraints(w, screen, margins, &minimumSize, &maximumSize);
     qCDebug(lcQpaWindows).nospace() << '>' << __FUNCTION__ << '<' << " min="
         << minimumSize.width() << ',' << minimumSize.height()
         << " max=" << maximumSize.width() << ',' << maximumSize.height()
@@ -1041,6 +1048,13 @@ void QWindowsGeometryHint::applyToMinMaxInfo(const QWindow *w,
     qCDebug(lcQpaWindows).nospace() << '<' << __FUNCTION__ << " out " << *mmi;
 }
 
+void QWindowsGeometryHint::applyToMinMaxInfo(const QWindow *w,
+                                             const QMargins &margins,
+                                             MINMAXINFO *mmi)
+{
+    applyToMinMaxInfo(w, w->screen(), margins, mmi);
+}
+
 bool QWindowsGeometryHint::positionIncludesFrame(const QWindow *w)
 {
     return qt_window_private(const_cast<QWindow *>(w))->positionPolicy
@@ -1226,11 +1240,12 @@ void QWindowsForeignWindow::setVisible(bool visible)
     \ingroup qt-lighthouse-win
 */
 
-QWindowCreationContext::QWindowCreationContext(const QWindow *w,
+QWindowCreationContext::QWindowCreationContext(const QWindow *w, const QScreen *s,
                                                const QRect &geometryIn, const QRect &geometry,
                                                const QMargins &cm,
                                                DWORD style, DWORD exStyle) :
     window(w),
+    screen(s),
     requestedGeometryIn(geometryIn),
     requestedGeometry(geometry),
     obtainedPos(geometryIn.topLeft()),
@@ -1270,7 +1285,7 @@ QWindowCreationContext::QWindowCreationContext(const QWindow *w,
 
 void QWindowCreationContext::applyToMinMaxInfo(MINMAXINFO *mmi) const
 {
-    QWindowsGeometryHint::applyToMinMaxInfo(window, margins + customMargins, mmi);
+    QWindowsGeometryHint::applyToMinMaxInfo(window, screen, margins + customMargins, mmi);
 }
 
 /*!

src/plugins/platforms/windows/qwindowswindow.h

@@ -66,9 +66,12 @@ struct QWindowsGeometryHint
     static QMargins frame(const QWindow *w, const QRect &geometry,
                           DWORD style, DWORD exStyle);
     static bool handleCalculateSize(const QMargins &customMargins, const MSG &msg, LRESULT *result);
+    static void applyToMinMaxInfo(const QWindow *w, const QScreen *screen,
+                                  const QMargins &margins, MINMAXINFO *mmi);
     static void applyToMinMaxInfo(const QWindow *w, const QMargins &margins,
                                   MINMAXINFO *mmi);
-    static void frameSizeConstraints(const QWindow *w, const QMargins &margins,
+    static void frameSizeConstraints(const QWindow *w, const QScreen *screen,
+                                     const QMargins &margins,
                                      QSize *minimumSize, QSize *maximumSize);
     static inline QPoint mapToGlobal(HWND hwnd, const QPoint &);
     static inline QPoint mapToGlobal(const QWindow *w, const QPoint &);
@@ -80,13 +83,16 @@ struct QWindowsGeometryHint
 
 struct QWindowCreationContext
 {
-    explicit QWindowCreationContext(const QWindow *w,
+    explicit QWindowCreationContext(const QWindow *w, const QScreen *s,
                                     const QRect &geometryIn, const QRect &geometry,
                                     const QMargins &customMargins,
                                     DWORD style, DWORD exStyle);
     void applyToMinMaxInfo(MINMAXINFO *mmi) const;
 
     const QWindow *window;
+    // The screen to use to scale size constraints, etc. Might differ from the
+    // screen of the window after QPlatformWindow::initialGeometry() (QTBUG-77307).
+    const QScreen *screen;
     QRect requestedGeometryIn; // QWindow scaled
     QRect requestedGeometry; // after QPlatformWindow::initialGeometry()
     QPoint obtainedPos;