Expose screen change event to widgets so that they can check the dpr

Unlike ordinary widgets, the ones that have OpenGL framebuffers must know
about screen changes because the device pixel ratio may be different on
the new screen. Add an internal event, ScreenChangeInternal, as the
counterpart to WindowChangeInternal.

Change-Id: I5e55999838e4c0284e7d9832299f7cc6b541ee3f
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>

5 files changed, 30 insertions, 4 deletions

diff --git a/src/corelib/kernel/qcoreevent.cpp b/src/corelib/kernel/qcoreevent.cpp
index bc54a2ae74..044128998b 100644
--- a/src/corelib/kernel/qcoreevent.cpp
+++ b/src/corelib/kernel/qcoreevent.cpp
@@ -278,6 +278,7 @@ QT_BEGIN_NAMESPACE
     \omitvalue FutureCallOut
     \omitvalue NativeGesture
     \omitvalue WindowChangeInternal
+    \omitvalue ScreenChangeInternal
 */
 
 /*!
diff --git a/src/corelib/kernel/qcoreevent.h b/src/corelib/kernel/qcoreevent.h
index cd7689f842..bd5a5187e3 100644
--- a/src/corelib/kernel/qcoreevent.h
+++ b/src/corelib/kernel/qcoreevent.h
@@ -281,6 +281,7 @@ public:
         ApplicationStateChange = 214,
 
         WindowChangeInternal = 215,             // internal for QQuickWidget
+        ScreenChangeInternal = 216,
 
         // 512 reserved for Qt Jambi's MetaCall event
         // 513 reserved for Qt Jambi's DeleteOnMainThread event
diff --git a/src/widgets/kernel/qopenglwidget.cpp b/src/widgets/kernel/qopenglwidget.cpp
index 8f7751618d..4eee4e526d 100644
--- a/src/widgets/kernel/qopenglwidget.cpp
+++ b/src/widgets/kernel/qopenglwidget.cpp
@@ -1061,6 +1061,10 @@ bool QOpenGLWidget::event(QEvent *e)
                 d->recreateFbo();
         }
         break;
+    case QEvent::ScreenChangeInternal:
+        if (d->initialized && d->paintDevice->devicePixelRatio() != devicePixelRatio())
+            d->recreateFbo();
+        break;
     default:
         break;
     }
diff --git a/src/widgets/kernel/qwidgetwindow.cpp b/src/widgets/kernel/qwidgetwindow.cpp
index b255bc16f9..dccd7ae2c8 100644
--- a/src/widgets/kernel/qwidgetwindow.cpp
+++ b/src/widgets/kernel/qwidgetwindow.cpp
@@ -99,7 +99,7 @@ QWidgetWindow::QWidgetWindow(QWidget *widget)
         setSurfaceType(QSurface::RasterGLSurface);
     }
     connect(m_widget, &QObject::objectNameChanged, this, &QWidgetWindow::updateObjectName);
-    connect(this, SIGNAL(screenChanged(QScreen*)), this, SLOT(repaintWindow()));
+    connect(this, SIGNAL(screenChanged(QScreen*)), this, SLOT(handleScreenChange()));
 }
 
 QWidgetWindow::~QWidgetWindow()
@@ -558,8 +558,27 @@ void QWidgetWindow::updateGeometry()
     m_widget->data->fstrut_dirty = false;
 }
 
-// Invalidates the backing store buffer and repaints immediately.
-// ### Qt 5.4: replace with QUpdateWindowRequestEvent.
+static void sendScreenChangeRecursively(QWidget *widget)
+{
+    QEvent e(QEvent::ScreenChangeInternal);
+    QApplication::sendEvent(widget, &e);
+    QWidgetPrivate *d = QWidgetPrivate::get(widget);
+    for (int i = 0; i < d->children.size(); ++i) {
+        QWidget *w = qobject_cast<QWidget *>(d->children.at(i));
+        if (w)
+            sendScreenChangeRecursively(w);
+    }
+}
+
+void QWidgetWindow::handleScreenChange()
+{
+    // Send an event recursively to the widget and its children.
+    sendScreenChangeRecursively(m_widget);
+
+    // Invalidate the backing store buffer and repaint immediately.
+    repaintWindow();
+}
+
 void QWidgetWindow::repaintWindow()
 {
     if (!m_widget->isVisible() || !m_widget->updatesEnabled())
diff --git a/src/widgets/kernel/qwidgetwindow_p.h b/src/widgets/kernel/qwidgetwindow_p.h
index be2adddff5..87ad7a4bd4 100644
--- a/src/widgets/kernel/qwidgetwindow_p.h
+++ b/src/widgets/kernel/qwidgetwindow_p.h
@@ -101,9 +101,10 @@ protected:
 
 private slots:
     void updateObjectName();
-    void repaintWindow();
+    void handleScreenChange();
 
 private:
+    void repaintWindow();
     void updateGeometry();
     void updateNormalGeometry();