X11 devicePixelRatio screen mapping fix

Fix screen detection and window geometry when screens have
different displayPixelRatios.

We must use the native coordinate system to figure out which
screen a window belongs to. Also, when a window moves to a
screen with a different devicePixelRatio, we must recalculate
the Qt geometry.

Task-number: QTBUG-43713
Change-Id: I93063e37354ff88f3c8a13320b76dfb272e43a9c
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>

src/plugins/platforms/xcb/qxcbscreen.cpp

@@ -77,8 +77,10 @@ QXcbScreen::QXcbScreen(QXcbConnection *connection, xcb_screen_t *scr,
     // virtual size is known (probably back-calculated from DPI and resolution)
     if (m_sizeMillimeters.isEmpty())
         m_sizeMillimeters = m_virtualSizeMillimeters;
-    if (m_geometry.isEmpty())
+    if (m_geometry.isEmpty()) {
         m_geometry = QRect(QPoint(), m_virtualSize/dpr);
+        m_nativeGeometry = QRect(QPoint(), m_virtualSize);
+    }
     if (m_availableGeometry.isEmpty())
         m_availableGeometry = m_geometry;
 
@@ -461,6 +463,7 @@ void QXcbScreen::updateGeometry(xcb_timestamp_t timestamp)
     m_devicePixelRatio = qRound(dpi/96);
     const int dpr = int(devicePixelRatio()); // we may override m_devicePixelRatio
     m_geometry = QRect(xGeometry.topLeft()/dpr, xGeometry.size()/dpr);
+    m_nativeGeometry = QRect(xGeometry.topLeft(), xGeometry.size());
     m_availableGeometry = QRect(xAvailableGeometry.topLeft()/dpr, xAvailableGeometry.size()/dpr);
 
     QWindowSystemInterface::handleScreenGeometryChange(QPlatformScreen::screen(), m_geometry, m_availableGeometry);

src/plugins/platforms/xcb/qxcbscreen.h

@@ -62,6 +62,7 @@ public:
     QWindow *topLevelAt(const QPoint &point) const;
 
     QRect geometry() const { return m_geometry; }
+    QRect nativeGeometry() const { return m_nativeGeometry; }
     QRect availableGeometry() const {return m_availableGeometry;}
     int depth() const { return m_screen->root_depth; }
     QImage::Format format() const;
@@ -114,6 +115,7 @@ private:
     QSizeF m_outputSizeMillimeters;
     QSizeF m_sizeMillimeters;
     QRect m_geometry;
+    QRect m_nativeGeometry;
     QRect m_availableGeometry;
     QSize m_virtualSize;
     QSizeF m_virtualSizeMillimeters;

src/plugins/platforms/xcb/qxcbwindow.cpp

@@ -1831,6 +1831,23 @@ void QXcbWindow::handleClientMessageEvent(const xcb_client_message_event_t *even
     }
 }
 
+// Temporary workaround for bug in QPlatformScreen::screenForNativeGeometry
+// we need the native geometries to detect our screen, but that's not
+// available in cross-platform code. Will be fixed properly when highDPI
+// support is refactored to expose the native coordinate system.
+
+QPlatformScreen *QXcbWindow::screenForNativeGeometry(const QRect &newGeometry) const
+{
+    QXcbScreen *currentScreen = static_cast<QXcbScreen*>(screen());
+    if (!parent() && !currentScreen->nativeGeometry().intersects(newGeometry)) {
+        Q_FOREACH (QPlatformScreen* screen, currentScreen->virtualSiblings()) {
+            if (static_cast<QXcbScreen*>(screen)->nativeGeometry().intersects(newGeometry))
+                return screen;
+        }
+    }
+    return currentScreen;
+}
+
 void QXcbWindow::handleConfigureNotifyEvent(const xcb_configure_notify_event_t *event)
 {
     bool fromSendEvent = (event->response_type & 0x80);
@@ -1847,15 +1864,23 @@ void QXcbWindow::handleConfigureNotifyEvent(const xcb_configure_notify_event_t *
         }
     }
 
-    QRect rect = mapFromNative(QRect(pos, QSize(event->width, event->height)), int(devicePixelRatio()));
+    const int dpr = devicePixelRatio();
+    const QRect nativeRect = QRect(pos, QSize(event->width, event->height));
+    const QRect rect = mapFromNative(nativeRect, dpr);
 
     QPlatformWindow::setGeometry(rect);
     QWindowSystemInterface::handleGeometryChange(window(), rect);
 
-    QPlatformScreen *newScreen = screenForGeometry(rect);
+    QPlatformScreen *newScreen = screenForNativeGeometry(nativeRect);
     if (newScreen != m_screen) {
         m_screen = static_cast<QXcbScreen*>(newScreen);
         QWindowSystemInterface::handleWindowScreenChanged(window(), newScreen->screen());
+        int newDpr = devicePixelRatio();
+        if (newDpr != dpr) {
+            QRect newRect = mapFromNative(nativeRect, newDpr);
+            QPlatformWindow::setGeometry(newRect);
+            QWindowSystemInterface::handleGeometryChange(window(), newRect);
+        }
     }
 
     m_configureNotifyPending = false;

src/plugins/platforms/xcb/qxcbwindow.h

@@ -154,6 +154,8 @@ public:
 
     qreal devicePixelRatio() const;
 
+    QPlatformScreen *screenForNativeGeometry(const QRect &newGeometry) const;
+
 public Q_SLOTS:
     void updateSyncRequestCounter();