Windows QPA: Better recover from removed screens when fullscreen

QWindowsWindow::handleResized would call isFullScreen_sys which checks
if the window's screen geometry matches the one of the window. When
switching back from fullscreen, Windows will have set the geometry to
fill the next window, but we don't switch QScreen until later in that
function, inside handleGeometryChange. This would result in our window
to take the whole screen geometry, but the FullScreen state wouldn't
be transferred to the new screen.

Fix the issue by using screenForGeometry and check if we are fullscreen
on any screen.

Also make sure that we check the validity of m_savedFrameGeometry when
restoring after a screen remove, since we would previously restore to an
area not covered by any screen anymore.

Change-Id: I43bc02738007918e9a26c1d27a699c51d3365034
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 10 insertions, 4 deletions

diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 0028ad1bd0..79dce2fc43 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -1750,10 +1750,9 @@ bool QWindowsWindow::isFullScreen_sys() const
     const QWindow *w = window();
     if (!w->isTopLevel())
         return false;
-    const QScreen *screen = w->screen();
-    if (!screen)
-        screen = QGuiApplication::primaryScreen();
-    return screen && geometry_sys() == QHighDpi::toNativePixels(screen->geometry(), w);
+    QRect geometry = geometry_sys();
+    QPlatformScreen *screen = screenForGeometry(geometry);
+    return screen && geometry == QHighDpi::toNativePixels(screen->geometry(), screen);
 }
 
 /*!
@@ -1825,6 +1824,13 @@ void QWindowsWindow::setWindowState_sys(Qt::WindowState newState)
                 newStyle |= WS_VISIBLE;
             setStyle(newStyle);
 
+            const QScreen *screen = window()->screen();
+            if (!screen)
+                screen = QGuiApplication::primaryScreen();
+            // That area of the virtual desktop might not be covered by a screen anymore.
+            if (!screen->geometry().intersects(m_savedFrameGeometry))
+                m_savedFrameGeometry.moveTo(screen->geometry().topLeft());
+
             UINT swpf = SWP_FRAMECHANGED | SWP_NOZORDER | SWP_NOACTIVATE;
             if (!m_savedFrameGeometry.isValid())
                 swpf |= SWP_NOSIZE | SWP_NOMOVE;