Make sure QGraphicsScene::update() only requires one event-loop

iteration before the views are updated.

A full scene update (scene.update()) already supported it because the
scene called update() on the views directly. However, partially scene
updates (scene.update(rect)) required two event-loop iterations
before the views were updated.

Auto-test included.

4 files changed, 46 insertions, 15 deletions

diff --git a/src/gui/graphicsview/qgraphicsscene.cpp b/src/gui/graphicsview/qgraphicsscene.cpp
index c8e178a143..48d8788e4f 100644
--- a/src/gui/graphicsview/qgraphicsscene.cpp
+++ b/src/gui/graphicsview/qgraphicsscene.cpp
@@ -357,6 +357,9 @@ void QGraphicsScenePrivate::_q_emitUpdated()
         updateAll = false;
         for (int i = 0; i < views.size(); ++i)
             views.at(i)->d_func()->processPendingUpdates();
+        // It's important that we update all views before we dispatch, hence two for-loops.
+        for (int i = 0; i < views.size(); ++i)
+            views.at(i)->d_func()->dispatchPendingUpdateRequests();
         return;
     }
 
@@ -447,13 +450,8 @@ void QGraphicsScenePrivate::_q_processDirtyItems()
     }
 
     // Immediately dispatch all pending update requests on the views.
-    for (int i = 0; i < views.size(); ++i) {
-        QWidget *viewport = views.at(i)->d_func()->viewport;
-        if (qt_widget_private(viewport)->paintOnScreen())
-            QCoreApplication::sendPostedEvents(viewport, QEvent::UpdateRequest);
-        else
-            QCoreApplication::sendPostedEvents(viewport->window(), QEvent::UpdateRequest);
-    }
+    for (int i = 0; i < views.size(); ++i)
+        views.at(i)->d_func()->dispatchPendingUpdateRequests();
 }
 
 /*!
@@ -2730,7 +2728,7 @@ void QGraphicsScene::update(const QRectF &rect)
         if (directUpdates) {
             // Update all views.
             for (int i = 0; i < d->views.size(); ++i)
-                d->views.at(i)->d_func()->updateAll();
+                d->views.at(i)->d_func()->fullUpdatePending = true;
         }
     } else {
         if (directUpdates) {
diff --git a/src/gui/graphicsview/qgraphicsview.cpp b/src/gui/graphicsview/qgraphicsview.cpp
index bcfd68cb57..1cea8db616 100644
--- a/src/gui/graphicsview/qgraphicsview.cpp
+++ b/src/gui/graphicsview/qgraphicsview.cpp
@@ -821,13 +821,9 @@ void QGraphicsViewPrivate::processPendingUpdates()
     if (!scene)
         return;
 
-    if (fullUpdatePending) { // We have already called viewport->update()
-        dirtyBoundingRect = QRect();
-        dirtyRegion = QRegion();
-        return;
-    }
-
-    if (viewportUpdateMode == QGraphicsView::BoundingRectViewportUpdate) {
+    if (fullUpdatePending) {
+        viewport->update();
+    } else if (viewportUpdateMode == QGraphicsView::BoundingRectViewportUpdate) {
         if (optimizationFlags & QGraphicsView::DontAdjustForAntialiasing)
             viewport->update(dirtyBoundingRect.adjusted(-1, -1, 1, 1));
         else
diff --git a/src/gui/graphicsview/qgraphicsview_p.h b/src/gui/graphicsview/qgraphicsview_p.h
index 0fa8b34689..62a2b84f74 100644
--- a/src/gui/graphicsview/qgraphicsview_p.h
+++ b/src/gui/graphicsview/qgraphicsview_p.h
@@ -58,6 +58,7 @@
 #if !defined(QT_NO_GRAPHICSVIEW) || (QT_EDITION & QT_MODULE_GRAPHICSVIEW) != QT_MODULE_GRAPHICSVIEW
 
 #include <QtGui/qevent.h>
+#include <QtCore/qcoreapplication.h>
 #include "qgraphicssceneevent.h"
 #include <QtGui/qstyleoption.h>
 #include <private/qabstractscrollarea_p.h>
@@ -168,6 +169,15 @@ public:
         dirtyBoundingRect = QRect();
         dirtyRegion = QRegion();
     }
+
+    inline void dispatchPendingUpdateRequests()
+    {
+        if (qt_widget_private(viewport)->paintOnScreen())
+            QCoreApplication::sendPostedEvents(viewport, QEvent::UpdateRequest);
+        else
+            QCoreApplication::sendPostedEvents(viewport->window(), QEvent::UpdateRequest);
+    }
+
     bool updateRect(const QRect &rect);
     bool updateRegion(const QRegion &region);
     bool updateSceneSlotReimplementedChecked;
diff --git a/tests/auto/qgraphicsscene/tst_qgraphicsscene.cpp b/tests/auto/qgraphicsscene/tst_qgraphicsscene.cpp
index e9d6f1dedb..f7ea4cecc8 100644
--- a/tests/auto/qgraphicsscene/tst_qgraphicsscene.cpp
+++ b/tests/auto/qgraphicsscene/tst_qgraphicsscene.cpp
@@ -236,6 +236,7 @@ private slots:
     void contextMenuEvent();
     void contextMenuEvent_ItemIgnoresTransformations();
     void update();
+    void update2();
     void views();
     void event();
     void eventsToDisabledItems();
@@ -2779,6 +2780,32 @@ void tst_QGraphicsScene::update()
     QCOMPARE(region, QRectF(-100, -100, 200, 200));
 }
 
+void tst_QGraphicsScene::update2()
+{
+    QGraphicsScene scene;
+    scene.setSceneRect(-200, -200, 200, 200);
+    CustomView view;
+    view.setScene(&scene);
+    view.show();
+#ifdef Q_WS_X11
+    qt_x11_wait_for_window_manager(&view);
+#endif
+    QTest::qWait(250);
+    view.repaints = 0;
+
+    // Make sure QGraphicsScene::update only requires one event-loop iteration
+    // before the view is updated.
+    scene.update();
+    qApp->processEvents();
+    QCOMPARE(view.repaints, 1);
+    view.repaints = 0;
+
+    // The same for partial scene updates.
+    scene.update(QRectF(-100, -100, 100, 100));
+    qApp->processEvents();
+    QCOMPARE(view.repaints, 1);
+}
+
 void tst_QGraphicsScene::views()
 {
     QGraphicsScene scene;