Avoid flicker when invalidate is propagated in a widget/layout hierarchy

* Do not call invalidate from activateRecursive().
  This resulted in that a layout was invalidated as many times as there
  were items in the layout.

* Several improvements. Do not call resize(size()) too often.
  Calling resize() from the widgetEvent() is not very nice though...

* Remove commented out code

* make sure layout is activated even if the widget does not change size

* activate the layout if the resize is same as size()

* In order to not break existing apps, make this an opt-in feature
  with QGraphicsLayout::setInstantInvalidatePropagation(true);

Reviewed-by: Frederik Gladhorn
Reviewed-by: John Tapsell

src/gui/graphicsview/qgraphicslayout.cpp

@@ -269,12 +269,20 @@ void QGraphicsLayout::activate()
         return;
     Q_ASSERT(!parentItem->isLayout());
 
-    setGeometry(parentItem->contentsRect());    // relayout children
+    if (QGraphicsLayout::instantInvalidatePropagation()) {
+        QGraphicsWidget *parentWidget = static_cast<QGraphicsWidget*>(parentItem);
+        if (!parentWidget->parentLayoutItem()) {
+            // we've reached the topmost widget, resize it
+            bool wasResized = parentWidget->testAttribute(Qt::WA_Resized);
+            parentWidget->resize(parentWidget->size());
+            parentWidget->setAttribute(Qt::WA_Resized, wasResized);
+        }
 
-    // ### bug, should be parentItem ?
+        setGeometry(parentItem->contentsRect());    // relayout children
-    parentLayoutItem()->updateGeometry();            // bubble up; will set activated to false
+    } else {
-    // ### too many resizes? maybe we should walk up the chain to the
+        setGeometry(parentItem->contentsRect());    // relayout children
-    // ### top-level layouted layoutItem and call activate there.
+        parentLayoutItem()->updateGeometry();
+    }
 }
 
 /*!
@@ -300,32 +308,36 @@ bool QGraphicsLayout::isActivated() const
 */
 void QGraphicsLayout::invalidate()
 {
-    // only mark layouts as invalid (activated = false) if we can post a LayoutRequest event.
+    if (QGraphicsLayout::instantInvalidatePropagation()) {
-    QGraphicsLayoutItem *layoutItem = this;
+        updateGeometry();
-    while (layoutItem && layoutItem->isLayout()) {
+    } else {
-        // we could call updateGeometry(), but what if that method
+        // only mark layouts as invalid (activated = false) if we can post a LayoutRequest event.
-        // does not call the base implementation? In addition, updateGeometry()
+        QGraphicsLayoutItem *layoutItem = this;
-        // does more than we need.
+        while (layoutItem && layoutItem->isLayout()) {
-        layoutItem->d_func()->sizeHintCacheDirty = true;
+            // we could call updateGeometry(), but what if that method
-        layoutItem->d_func()->sizeHintWithConstraintCacheDirty = true;
+            // does not call the base implementation? In addition, updateGeometry()
-        layoutItem = layoutItem->parentLayoutItem();
+            // does more than we need.
-    }
+            layoutItem->d_func()->sizeHintCacheDirty = true;
-    if (layoutItem) {
+            layoutItem->d_func()->sizeHintWithConstraintCacheDirty = true;
-        layoutItem->d_func()->sizeHintCacheDirty = true;
-        layoutItem->d_func()->sizeHintWithConstraintCacheDirty = true;
-    }
-
-    bool postIt = layoutItem ? !layoutItem->isLayout() : false;
-    if (postIt) {
-        layoutItem = this;
-        while (layoutItem && layoutItem->isLayout()
-                && static_cast<QGraphicsLayout*>(layoutItem)->d_func()->activated) {
-            static_cast<QGraphicsLayout*>(layoutItem)->d_func()->activated = false;
             layoutItem = layoutItem->parentLayoutItem();
         }
-        if (layoutItem && !layoutItem->isLayout()) {
+        if (layoutItem) {
-            // If a layout has a parent that is not a layout it must be a QGraphicsWidget.
+            layoutItem->d_func()->sizeHintCacheDirty = true;
-            QApplication::postEvent(static_cast<QGraphicsWidget *>(layoutItem), new QEvent(QEvent::LayoutRequest));
+            layoutItem->d_func()->sizeHintWithConstraintCacheDirty = true;
+        }
+
+        bool postIt = layoutItem ? !layoutItem->isLayout() : false;
+        if (postIt) {
+            layoutItem = this;
+            while (layoutItem && layoutItem->isLayout()
+                    && static_cast<QGraphicsLayout*>(layoutItem)->d_func()->activated) {
+                static_cast<QGraphicsLayout*>(layoutItem)->d_func()->activated = false;
+                layoutItem = layoutItem->parentLayoutItem();
+            }
+            if (layoutItem && !layoutItem->isLayout()) {
+                // If a layout has a parent that is not a layout it must be a QGraphicsWidget.
+                QApplication::postEvent(static_cast<QGraphicsWidget *>(layoutItem), new QEvent(QEvent::LayoutRequest));
+            }
         }
     }
 }
@@ -335,12 +347,27 @@ void QGraphicsLayout::invalidate()
 */
 void QGraphicsLayout::updateGeometry()
 {
-    QGraphicsLayoutItem::updateGeometry();
+    Q_D(QGraphicsLayout);
-    if (QGraphicsLayoutItem *parentItem = parentLayoutItem()) {
+    if (QGraphicsLayout::instantInvalidatePropagation()) {
-        if (parentItem->isLayout()) {
+        d->activated = false;
+        QGraphicsLayoutItem::updateGeometry();
+
+        QGraphicsLayoutItem *parentItem = parentLayoutItem();
+        if (!parentItem)
+            return;
+
+        if (parentItem->isLayout())
+            static_cast<QGraphicsLayout *>(parentItem)->invalidate();
+        else
             parentItem->updateGeometry();
-        } else {
+    } else {
-            invalidate();
+        QGraphicsLayoutItem::updateGeometry();
+        if (QGraphicsLayoutItem *parentItem = parentLayoutItem()) {
+            if (parentItem->isLayout()) {
+                parentItem->updateGeometry();
+            } else {
+                invalidate();
+            }
         }
     }
 }
@@ -446,6 +473,50 @@ void QGraphicsLayout::addChildLayoutItem(QGraphicsLayoutItem *layoutItem)
     d->addChildLayoutItem(layoutItem);
 }
 
+static bool g_instantInvalidatePropagation = false;
+
+/*!
+    \internal
+    \since 4.8
+    \see instantInvalidatePropagation
+
+    Calling this function with \a enable set to true will enable a feature that
+    makes propagation of invalidation up to ancestor layout items to be done in
+    one go. It will propagate up the parentLayoutItem() hierarchy until it has
+    reached the root. If the root item is a QGraphicsWidget, it will *post* a
+    layout request to it. When the layout request is consumed it will traverse
+    down the hierarchy of layouts and widgets and activate all layouts that is
+    invalid (not activated). This is the recommended behaviour.
+
+    If not set it will also propagate up the parentLayoutItem() hierarchy, but
+    it will stop at the \i first \i widget it encounters, and post a layout
+    request to the widget. When the layout request is consumed, this might
+    cause it to continue propagation up to the parentLayoutItem() of the
+    widget. It will continue in this fashion until it has reached a widget with
+    no parentLayoutItem(). This strategy might cause drawing artifacts, since
+    it is not done in one go, and the consumption of layout requests might be
+    interleaved by consumption of paint events, which might cause significant
+    flicker.
+    Note, this is not the recommended behavior, but for compatibility reasons
+    this is the default behaviour.
+*/
+void QGraphicsLayout::setInstantInvalidatePropagation(bool enable)
+{
+    g_instantInvalidatePropagation = enable;
+}
+
+/*!
+    \internal
+    \since 4.8
+    \see setInstantInvalidatePropagation
+
+    returns true if the complete widget/layout hierarchy is rearranged in one go.
+*/
+bool QGraphicsLayout::instantInvalidatePropagation()
+{
+    return g_instantInvalidatePropagation;
+}
+
 QT_END_NAMESPACE
 
 #endif //QT_NO_GRAPHICSVIEW

src/gui/graphicsview/qgraphicslayout.h

@@ -76,6 +76,8 @@ public:
     virtual QGraphicsLayoutItem *itemAt(int i) const = 0;
     virtual void removeAt(int index) = 0;
 
+    static void setInstantInvalidatePropagation(bool enable);
+    static bool instantInvalidatePropagation();
 protected:
     QGraphicsLayout(QGraphicsLayoutPrivate &, QGraphicsLayoutItem *);
     void addChildLayoutItem(QGraphicsLayoutItem *layoutItem);

src/gui/graphicsview/qgraphicslayout_p.cpp

@@ -180,9 +180,14 @@ void QGraphicsLayoutPrivate::activateRecursive(QGraphicsLayoutItem *item)
 {
     if (item->isLayout()) {
         QGraphicsLayout *layout = static_cast<QGraphicsLayout *>(item);
-        if (layout->d_func()->activated)
+        if (layout->d_func()->activated) {
-            layout->invalidate();
+            if (QGraphicsLayout::instantInvalidatePropagation()) {
-
+                return;
+            } else {
+                layout->invalidate();   // ### LOOKS SUSPICIOUSLY WRONG!!???
+            }
+        }
+        
         for (int i = layout->count() - 1; i >= 0; --i) {
             QGraphicsLayoutItem *childItem = layout->itemAt(i);
             if (childItem)

src/gui/graphicsview/qgraphicslinearlayout.cpp

@@ -275,17 +275,16 @@ void QGraphicsLinearLayout::insertItem(int index, QGraphicsLayoutItem *item)
         qWarning("QGraphicsLinearLayout::insertItem: cannot insert itself");
         return;
     }
-    Q_ASSERT(item);
 
-    //the order of the following instructions is very important because
-    //invalidating the layout before adding the child item will make the layout happen
-    //before we try to paint the item
-    invalidate();
     d->addChildLayoutItem(item);
 
     d->fixIndex(&index);
     d->engine.insertRow(index, d->orientation);
     new QGridLayoutItem(&d->engine, item, d->gridRow(index), d->gridColumn(index), 1, 1, 0, index);
+    //the order of the following instructions is very important because
+    //invalidating the layout before adding the child item will make the layout happen
+    //before we try to paint the item
+    invalidate();
 }
 
 /*!

src/gui/graphicsview/qgraphicswidget.cpp

@@ -354,8 +354,10 @@ void QGraphicsWidget::setGeometry(const QRectF &rect)
         newGeom = rect;
         newGeom.setSize(rect.size().expandedTo(effectiveSizeHint(Qt::MinimumSize))
                                    .boundedTo(effectiveSizeHint(Qt::MaximumSize)));
-        if (newGeom == d->geom)
+
-            return;
+        if (newGeom == d->geom) {
+            goto relayoutChildrenAndReturn;
+        }
 
         // setPos triggers ItemPositionChange, which can adjust position
         wd->inSetGeometry = 1;
@@ -363,8 +365,9 @@ void QGraphicsWidget::setGeometry(const QRectF &rect)
         wd->inSetGeometry = 0;
         newGeom.moveTopLeft(pos());
 
-        if (newGeom == d->geom)
+        if (newGeom == d->geom) {
-           return;
+            goto relayoutChildrenAndReturn;
+        }
 
          // Update and prepare to change the geometry (remove from index) if the size has changed.
         if (wd->scene) {
@@ -375,35 +378,54 @@ void QGraphicsWidget::setGeometry(const QRectF &rect)
     }
 
     // Update the layout item geometry
-    bool moved = oldPos != pos();
+    {
-    if (moved) {
+        bool moved = oldPos != pos();
-        // Send move event.
+        if (moved) {
-        QGraphicsSceneMoveEvent event;
+            // Send move event.
-        event.setOldPos(oldPos);
+            QGraphicsSceneMoveEvent event;
-        event.setNewPos(pos());
+            event.setOldPos(oldPos);
-        QApplication::sendEvent(this, &event);
+            event.setNewPos(pos());
-        if (wd->inSetPos) {
+            QApplication::sendEvent(this, &event);
-            //set the new pos
+            if (wd->inSetPos) {
-            d->geom.moveTopLeft(pos());
+                //set the new pos
-            emit geometryChanged();
+                d->geom.moveTopLeft(pos());
-            return;
+                emit geometryChanged();
+                goto relayoutChildrenAndReturn;
+            }
+        }
+        QSizeF oldSize = size();
+        QGraphicsLayoutItem::setGeometry(newGeom);
+        // Send resize event
+        bool resized = newGeom.size() != oldSize;
+        if (resized) {
+            QGraphicsSceneResizeEvent re;
+            re.setOldSize(oldSize);
+            re.setNewSize(newGeom.size());
+            if (oldSize.width() != newGeom.size().width())
+                emit widthChanged();
+            if (oldSize.height() != newGeom.size().height())
+                emit heightChanged();
+            QGraphicsLayout *lay = wd->layout;
+            if (QGraphicsLayout::instantInvalidatePropagation()) {
+                if (!lay || lay->isActivated()) {
+                    QApplication::sendEvent(this, &re);
+                }
+            } else {
+                QApplication::sendEvent(this, &re);
+            }
         }
     }
-    QSizeF oldSize = size();
+
-    QGraphicsLayoutItem::setGeometry(newGeom);
-    // Send resize event
-    bool resized = newGeom.size() != oldSize;
-    if (resized) {
-        QGraphicsSceneResizeEvent re;
-        re.setOldSize(oldSize);
-        re.setNewSize(newGeom.size());
-        if (oldSize.width() != newGeom.size().width())
-            emit widthChanged();
-        if (oldSize.height() != newGeom.size().height())
-            emit heightChanged();
-        QApplication::sendEvent(this, &re);
-    }
     emit geometryChanged();
+relayoutChildrenAndReturn:
+    if (QGraphicsLayout::instantInvalidatePropagation()) {
+        if (QGraphicsLayout *lay = wd->layout) {
+            if (!lay->isActivated()) {
+                QEvent layoutRequest(QEvent::LayoutRequest);
+                QApplication::sendEvent(this, &layoutRequest);
+            }
+        }
+    }
 }
 
 /*!
@@ -1052,16 +1074,31 @@ void QGraphicsWidget::updateGeometry()
     QGraphicsLayoutItem *parentItem = parentLayoutItem();
 
     if (parentItem && parentItem->isLayout()) {
-        parentItem->updateGeometry();
+        if (QGraphicsLayout::instantInvalidatePropagation()) {
+            static_cast<QGraphicsLayout *>(parentItem)->invalidate();
+        } else {
+            parentItem->updateGeometry();
+        }
     } else {
         if (parentItem) {
+            // This is for custom layouting
             QGraphicsWidget *parentWid = parentWidget();    //###
             if (parentWid->isVisible())
                 QApplication::postEvent(parentWid, new QEvent(QEvent::LayoutRequest));
+        } else {
+            /**
+             * If this is the topmost widget, post a LayoutRequest event to the widget.
+             * When the event is received, it will start flowing all the way down to the leaf
+             * widgets in one go. This will make a relayout flicker-free.
+             */
+            if (QGraphicsLayout::instantInvalidatePropagation())
+                QApplication::postEvent(static_cast<QGraphicsWidget *>(this), new QEvent(QEvent::LayoutRequest));
+        }
+        if (!QGraphicsLayout::instantInvalidatePropagation()) {
+            bool wasResized = testAttribute(Qt::WA_Resized);
+            resize(size()); // this will restrict the size
+            setAttribute(Qt::WA_Resized, wasResized);
         }
-        bool wasResized = testAttribute(Qt::WA_Resized);
-        resize(size()); // this will restrict the size
-        setAttribute(Qt::WA_Resized, wasResized);
     }
 }
 

tests/auto/qgraphicsanchorlayout/tst_qgraphicsanchorlayout.cpp

@@ -1091,6 +1091,9 @@ void tst_QGraphicsAnchorLayout::setSpacing()
 #ifdef Q_WS_MAC
     QTest::qWait(200);
 #endif
+
+    // 21x21
+    QCOMPARE(p->size(), QSizeF(41, 41));
     QCOMPARE(a->geometry(), QRectF(0, 0, 20, 20));
     QCOMPARE(b->geometry(), QRectF(21, 0, 20, 20));
     QCOMPARE(c->geometry(), QRectF(0, 21, 41, 20));

tests/auto/qgraphicslayout/tst_qgraphicslayout.cpp

@@ -62,6 +62,7 @@ private slots:
     void compressLayoutRequest();
     void automaticReparenting();
     void verifyActivate();
+    void invalidate();
     void constructors();
     void alternativeLayoutItems();
     void ownership();
@@ -218,6 +219,7 @@ class TestLayout : public QGraphicsLinearLayout
         : QGraphicsLinearLayout(parent)
     {
         m_count = 0;
+        m_invalidateCount = 0;
     }
 
     void setGeometry(const QRectF &rect) {
@@ -226,7 +228,12 @@ class TestLayout : public QGraphicsLinearLayout
         QGraphicsLinearLayout::setGeometry(rect);
     }
 
+    void invalidate() {
+        ++m_invalidateCount;
+        QGraphicsLinearLayout::invalidate();
+    }
 
+    int m_invalidateCount;
     int m_count;
 };
 
@@ -251,6 +258,87 @@ void tst_QGraphicsLayout::verifyActivate()
 
 }
 
+void tst_QGraphicsLayout::invalidate()
+{
+    QGraphicsLayout::setInstantInvalidatePropagation(true);
+    QGraphicsScene scene;
+    QGraphicsView view(&scene);
+
+    TestGraphicsWidget *a = new TestGraphicsWidget;
+    scene.addItem(a);
+    TestLayout *alay = new TestLayout(a);
+    TestGraphicsWidget *b = new TestGraphicsWidget;
+    alay->addItem(b);
+    TestLayout *blay = new TestLayout(b);
+    TestGraphicsWidget *e = new TestGraphicsWidget;
+    blay->addItem(e);
+
+
+    TestGraphicsWidget *c = new TestGraphicsWidget;
+    alay->addItem(c);
+    TestLayout *clay = new TestLayout(c);
+    TestGraphicsWidget *f = new TestGraphicsWidget;
+    clay->addItem(f);
+
+    TestGraphicsWidget *d = new TestGraphicsWidget;
+    alay->addItem(d);
+    TestLayout *dlay = new TestLayout(d);
+    TestGraphicsWidget *g = new TestGraphicsWidget;
+    dlay->addItem(g);
+
+    view.show();
+
+    alay->m_invalidateCount = 0;
+    blay->m_invalidateCount = 0;
+    clay->m_invalidateCount = 0;
+    dlay->m_invalidateCount = 0;
+
+    QCoreApplication::sendPostedEvents();
+    QCoreApplication::processEvents();
+
+    alay->activate();
+    QCOMPARE(alay->isActivated(), true);
+    QCOMPARE(blay->isActivated(), true);
+    QCOMPARE(clay->isActivated(), true);
+    qDebug() << "alay->m_invalidateCount:" << alay->m_invalidateCount;
+    qDebug() << "blay->m_invalidateCount:" << blay->m_invalidateCount;
+    qDebug() << "clay->m_invalidateCount:" << clay->m_invalidateCount;
+    qDebug() << "dlay->m_invalidateCount:" << dlay->m_invalidateCount;
+
+    a->clearEventCount();
+    b->clearEventCount();
+    c->clearEventCount();
+
+    blay->invalidate();
+    QCOMPARE(alay->isActivated(), false);
+    QCOMPARE(blay->isActivated(), false);
+    QCOMPARE(clay->isActivated(), true);
+    QCOMPARE(a->eventCount(QEvent::LayoutRequest), 0);
+    QCOMPARE(b->eventCount(QEvent::LayoutRequest), 0);
+    QCOMPARE(c->eventCount(QEvent::LayoutRequest), 0);
+
+
+    alay->m_invalidateCount = 0;
+    blay->m_invalidateCount = 0;
+    clay->m_invalidateCount = 0;
+    dlay->m_invalidateCount = 0;
+    clay->invalidate();
+    QCOMPARE(alay->isActivated(), false);
+    QCOMPARE(blay->isActivated(), false);
+    QCOMPARE(clay->isActivated(), false);
+
+    QCoreApplication::sendPostedEvents();
+    QCOMPARE(a->eventCount(QEvent::LayoutRequest), 1);
+    QCOMPARE(b->eventCount(QEvent::LayoutRequest), 0);
+    QCOMPARE(c->eventCount(QEvent::LayoutRequest), 0);
+    qDebug() << "alay->m_invalidateCount:" << alay->m_invalidateCount;
+    qDebug() << "blay->m_invalidateCount:" << blay->m_invalidateCount;
+    qDebug() << "clay->m_invalidateCount:" << clay->m_invalidateCount;
+    qDebug() << "dlay->m_invalidateCount:" << dlay->m_invalidateCount;
+
+    QGraphicsLayout::setInstantInvalidatePropagation(false);
+}
+
 class Layout : public QGraphicsLayout
 {
 public:

tests/auto/qgraphicslinearlayout/tst_qgraphicslinearlayout.cpp

@@ -94,6 +94,7 @@ private slots:
     void itemSpacing();
     void setStretchFactor_data();
     void setStretchFactor();
+    void testStretch();
     void defaultStretchFactors_data();
     void defaultStretchFactors();
     void sizeHint_data();
@@ -667,6 +668,10 @@ void tst_QGraphicsLinearLayout::invalidate()
     layout.setContentsMargins(0, 0, 0, 0);
     view.show();
     widget->show();
+    //QTest::qWait(1000);
+    QTest::qWaitForWindowShown(&view);
+    qApp->processEvents();
+    layout.layoutRequest = 0;
 
     layout.setContentsMargins(1, 2, 3, 4);
     QApplication::sendPostedEvents(0, 0);
@@ -1130,6 +1135,41 @@ void tst_QGraphicsLinearLayout::setStretchFactor()
     delete widget;
 }
 
+void tst_QGraphicsLinearLayout::testStretch()
+{
+    QGraphicsScene scene;
+    QGraphicsView *view = new QGraphicsView(&scene);
+    QGraphicsWidget *form = new QGraphicsWidget(0, Qt::Window);
+
+    scene.addItem(form);
+    form->setMinimumSize(600, 600);
+    form->setMaximumSize(600, 600);
+    QGraphicsLinearLayout *layout = new QGraphicsLinearLayout(Qt::Horizontal, form);
+    QGraphicsWidget *w1 = new RectWidget;
+    w1->setPreferredSize(100,100);
+    w1->setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
+    QGraphicsWidget *w2 = new RectWidget;
+    w2->setPreferredSize(200,200);
+    w2->setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
+    layout->setSpacing(0);
+    layout->setContentsMargins(0, 0, 0, 0);
+    layout->addItem(w1);
+    layout->addStretch(2);
+    layout->addItem(w2);
+    QCOMPARE(layout->count(), 2);
+    QVERIFY(layout->itemAt(0) == w1);
+    QVERIFY(layout->itemAt(1) == w2);
+    layout->activate();
+
+    //view->setSceneRect(-50, -50, 800, 800);
+    //view->show();
+    //QTest::qWaitForWindowShown(view);
+    //QTest::qWait(5000);
+    QCOMPARE(form->geometry().size(), QSizeF(600,600));
+    QCOMPARE(w1->geometry(), QRectF(0, 0, 100, 100));
+    QCOMPARE(w2->geometry(), QRectF(400, 0, 200, 200));
+}
+
 void tst_QGraphicsLinearLayout::defaultStretchFactors_data()
 {
     QTest::addColumn<Qt::Orientation>("orientation");