Layouts: Use QQuickItemChangeListener for more things

Signal connections are expensive: even with qmlobject_connect, there's a bunch
of memory allocation. By avoiding the signal connections, we can do the same
thing essentially, a little faster.

This gives me another 15-20 RowLayout instances per frame when testing with
RowLayout containing 5 Rectangles on qmlbench (from ~139 to ~155 ops/frame).

Change-Id: I4448a28128dc251e40b6b06d642bae716af212f4
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

4 files changed, 51 insertions, 48 deletions

diff --git a/src/imports/layouts/qquicklayout.cpp b/src/imports/layouts/qquicklayout.cpp
index 07ada75a5f..3786d21727 100644
--- a/src/imports/layouts/qquicklayout.cpp
+++ b/src/imports/layouts/qquicklayout.cpp
@@ -763,18 +763,14 @@ void QQuickLayout::itemChange(ItemChange change, const ItemChangeData &value)
 {
     if (change == ItemChildAddedChange) {
         QQuickItem *item = value.item;
-        qmlobject_connect(item, QQuickItem, SIGNAL(implicitWidthChanged()), this, QQuickLayout, SLOT(invalidateSenderItem()));
-        qmlobject_connect(item, QQuickItem, SIGNAL(implicitHeightChanged()), this, QQuickLayout, SLOT(invalidateSenderItem()));
         qmlobject_connect(item, QQuickItem, SIGNAL(baselineOffsetChanged(qreal)), this, QQuickLayout, SLOT(invalidateSenderItem()));
-        QQuickItemPrivate::get(item)->addItemChangeListener(this, QQuickItemPrivate::SiblingOrder);
+        QQuickItemPrivate::get(item)->addItemChangeListener(this, QQuickItemPrivate::SiblingOrder | QQuickItemPrivate::ImplicitWidth | QQuickItemPrivate::ImplicitHeight | QQuickItemPrivate::Destroyed | QQuickItemPrivate::Visibility);
         if (isReady())
             updateLayoutItems();
     } else if (change == ItemChildRemovedChange) {
         QQuickItem *item = value.item;
-        qmlobject_disconnect(item, QQuickItem, SIGNAL(implicitWidthChanged()), this, QQuickLayout, SLOT(invalidateSenderItem()));
-        qmlobject_disconnect(item, QQuickItem, SIGNAL(implicitHeightChanged()), this, QQuickLayout, SLOT(invalidateSenderItem()));
         qmlobject_disconnect(item, QQuickItem, SIGNAL(baselineOffsetChanged(qreal)), this, QQuickLayout, SLOT(invalidateSenderItem()));
-        QQuickItemPrivate::get(item)->removeItemChangeListener(this, QQuickItemPrivate::SiblingOrder);
+        QQuickItemPrivate::get(item)->removeItemChangeListener(this, QQuickItemPrivate::SiblingOrder | QQuickItemPrivate::ImplicitWidth | QQuickItemPrivate::ImplicitHeight | QQuickItemPrivate::Destroyed | QQuickItemPrivate::Visibility);
         if (isReady())
             updateLayoutItems();
     }
@@ -812,6 +808,30 @@ void QQuickLayout::itemSiblingOrderChanged(QQuickItem *item)
     updateLayoutItems();
 }
 
+void QQuickLayout::itemImplicitWidthChanged(QQuickItem *item)
+{
+    if (!isReady() || item->signalsBlocked())
+        return;
+    invalidate(item);
+}
+
+void QQuickLayout::itemImplicitHeightChanged(QQuickItem *item)
+{
+    if (!isReady() || item->signalsBlocked())
+        return;
+    invalidate(item);
+}
+
+void QQuickLayout::itemDestroyed(QQuickItem *item)
+{
+    Q_UNUSED(item);
+}
+
+void QQuickLayout::itemVisibilityChanged(QQuickItem *item)
+{
+    Q_UNUSED(item);
+}
+
 void QQuickLayout::rearrange(const QSizeF &/*size*/)
 {
     m_dirty = false;
diff --git a/src/imports/layouts/qquicklayout_p.h b/src/imports/layouts/qquicklayout_p.h
index c7f04c1fed..eece6f8658 100644
--- a/src/imports/layouts/qquicklayout_p.h
+++ b/src/imports/layouts/qquicklayout_p.h
@@ -99,6 +99,10 @@ public:
 
     /* QQuickItemChangeListener */
     void itemSiblingOrderChanged(QQuickItem *item) Q_DECL_OVERRIDE;
+    void itemImplicitWidthChanged(QQuickItem *item) Q_DECL_OVERRIDE;
+    void itemImplicitHeightChanged(QQuickItem *item) Q_DECL_OVERRIDE;
+    void itemDestroyed(QQuickItem *item) Q_DECL_OVERRIDE;
+    void itemVisibilityChanged(QQuickItem *item) Q_DECL_OVERRIDE;
 
 protected:
     void updatePolish() Q_DECL_OVERRIDE;
diff --git a/src/imports/layouts/qquicklinearlayout.cpp b/src/imports/layouts/qquicklinearlayout.cpp
index 7fad395a29..13fdd496c2 100644
--- a/src/imports/layouts/qquicklinearlayout.cpp
+++ b/src/imports/layouts/qquicklinearlayout.cpp
@@ -303,17 +303,13 @@ QQuickGridLayoutBase::~QQuickGridLayoutBase()
 {
     Q_D(QQuickGridLayoutBase);
 
-    /* Avoid messy deconstruction, should give:
-        * Faster deconstruction
-        * Less risk of signals reaching already deleted objects
-    */
+    // Remove item listeners so we do not act on signalling unnecessarily
+    // (there is no point, as the layout will be torn down anyway).
     for (int i = 0; i < itemCount(); ++i) {
         QQuickItem *item = itemAt(i);
-        qmlobject_disconnect(item, QQuickItem, SIGNAL(destroyed()), this, QQuickGridLayoutBase, SLOT(onItemDestroyed()));
-        qmlobject_disconnect(item, QQuickItem, SIGNAL(visibleChanged()), this, QQuickGridLayoutBase, SLOT(onItemVisibleChanged()));
-        qmlobject_disconnect(item, QQuickItem, SIGNAL(implicitWidthChanged()), this, QQuickGridLayoutBase, SLOT(invalidateSenderItem()));
-        qmlobject_disconnect(item, QQuickItem, SIGNAL(implicitHeightChanged()), this, QQuickGridLayoutBase, SLOT(invalidateSenderItem()));
+        QQuickItemPrivate::get(item)->removeItemChangeListener(this, QQuickItemPrivate::SiblingOrder | QQuickItemPrivate::ImplicitWidth | QQuickItemPrivate::ImplicitHeight | QQuickItemPrivate::Destroyed | QQuickItemPrivate::Visibility);
     }
+
     delete d->styleInfo;
 }
 
@@ -436,23 +432,6 @@ int QQuickGridLayoutBase::itemCount() const
     return d->engine.itemCount();
 }
 
-void QQuickGridLayoutBase::itemChange(ItemChange change, const ItemChangeData &value)
-{
-    if (change == ItemChildAddedChange) {
-        quickLayoutDebug() << "ItemChildAddedChange";
-        QQuickItem *item = value.item;
-        qmlobject_connect(item, QQuickItem, SIGNAL(destroyed()), this, QQuickGridLayoutBase, SLOT(onItemDestroyed()));
-        qmlobject_connect(item, QQuickItem, SIGNAL(visibleChanged()), this, QQuickGridLayoutBase, SLOT(onItemVisibleChanged()));
-    } else if (change == ItemChildRemovedChange) {
-        quickLayoutDebug() << "ItemChildRemovedChange";
-        QQuickItem *item = value.item;
-        qmlobject_disconnect(item, QQuickItem, SIGNAL(destroyed()), this, QQuickGridLayoutBase, SLOT(onItemDestroyed()));
-        qmlobject_disconnect(item, QQuickItem, SIGNAL(visibleChanged()), this, QQuickGridLayoutBase, SLOT(onItemVisibleChanged()));
-    }
-
-    QQuickLayout::itemChange(change, value);
-}
-
 void QQuickGridLayoutBase::removeGridItem(QGridLayoutItem *gridItem)
 {
     Q_D(QQuickGridLayoutBase);
@@ -461,28 +440,29 @@ void QQuickGridLayoutBase::removeGridItem(QGridLayoutItem *gridItem)
     d->engine.removeRows(index, 1, d->orientation);
 }
 
-void QQuickGridLayoutBase::onItemVisibleChanged()
-{
-    if (!isReady())
-        return;
-    quickLayoutDebug() << "QQuickGridLayoutBase::onItemVisibleChanged";
-    updateLayoutItems();
-}
-
-void QQuickGridLayoutBase::onItemDestroyed()
+void QQuickGridLayoutBase::itemDestroyed(QQuickItem *item)
 {
     if (!isReady())
         return;
     Q_D(QQuickGridLayoutBase);
-    quickLayoutDebug() << "QQuickGridLayoutBase::onItemDestroyed";
-    QQuickItem *inDestruction = static_cast<QQuickItem *>(sender());
-    if (QQuickGridLayoutItem *gridItem = d->engine.findLayoutItem(inDestruction)) {
+    quickLayoutDebug() << "QQuickGridLayoutBase::itemDestroyed";
+    if (QQuickGridLayoutItem *gridItem = d->engine.findLayoutItem(item)) {
         removeGridItem(gridItem);
         delete gridItem;
         invalidate();
     }
 }
 
+void QQuickGridLayoutBase::itemVisibilityChanged(QQuickItem *item)
+{
+    Q_UNUSED(item);
+
+    if (!isReady())
+        return;
+    quickLayoutDebug() << "QQuickGridLayoutBase::itemVisibilityChanged";
+    updateLayoutItems();
+}
+
 void QQuickGridLayoutBase::rearrange(const QSizeF &size)
 {
     Q_D(QQuickGridLayoutBase);
diff --git a/src/imports/layouts/qquicklinearlayout_p.h b/src/imports/layouts/qquicklinearlayout_p.h
index 86404f8d79..c289416540 100644
--- a/src/imports/layouts/qquicklinearlayout_p.h
+++ b/src/imports/layouts/qquicklinearlayout_p.h
@@ -77,6 +77,10 @@ public:
     Qt::LayoutDirection effectiveLayoutDirection() const;
     void setAlignment(QQuickItem *item, Qt::Alignment align) Q_DECL_OVERRIDE;
 
+    /* QQuickItemChangeListener */
+    void itemDestroyed(QQuickItem *item) Q_DECL_OVERRIDE;
+    void itemVisibilityChanged(QQuickItem *item) Q_DECL_OVERRIDE;
+
 protected:
     void updateLayoutItems() Q_DECL_OVERRIDE;
     QQuickItem *itemAt(int index) const Q_DECL_OVERRIDE;
@@ -84,15 +88,10 @@ protected:
 
     void rearrange(const QSizeF &size) Q_DECL_OVERRIDE;
     virtual void insertLayoutItems() {}
-    void itemChange(ItemChange change, const ItemChangeData &data) Q_DECL_OVERRIDE;
 
 signals:
     Q_REVISION(1) void layoutDirectionChanged();
 
-protected slots:
-    void onItemVisibleChanged();
-    void onItemDestroyed();
-
 private:
     void removeGridItem(QGridLayoutItem *gridItem);
     Q_DECLARE_PRIVATE(QQuickGridLayoutBase)