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>

1 files changed, 26 insertions, 6 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;