Move from a count of cursors, to storing whether or not a subtree has a cursor.

Calculation of this is going to be slower (of course) as we have to recurse the
children, but this only happens when unsetting a cursor or removing a child item
from a tree that had a cursor.

On the other hand, wasting 4 bytes per ExtraData plus padding is quite a large
concern, and it was also forcing allocation of ExtraData for an entire tree that
had a cursor set.

This also reduces the size of ExtraData from 152 down to 144 bytes through
reordering of members on x86_64.

Change-Id: Iab14ee71c762285bf4448fc86399070263eb118d
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

3 files changed, 33 insertions, 19 deletions

diff --git a/src/quick/items/qquickitem.cpp b/src/quick/items/qquickitem.cpp
index b68a9b5455..3aff1f0dfc 100644
--- a/src/quick/items/qquickitem.cpp
+++ b/src/quick/items/qquickitem.cpp
@@ -2722,8 +2722,11 @@ void QQuickItemPrivate::addChild(QQuickItem *child)
 
 #ifndef QT_NO_CURSOR
     QQuickItemPrivate *childPrivate = QQuickItemPrivate::get(child);
-    if (childPrivate->extra.isAllocated())
-        incrementCursorCount(childPrivate->extra.value().numItemsWithCursor);
+
+    // if the added child has a cursor and we do not currently have any children
+    // with cursors, bubble the notification up
+    if (childPrivate->hasCursorInChild && !hasCursorInChild)
+        setHasCursorInChild(true);
 #endif
 
     markSortedChildrenDirty(child);
@@ -2745,8 +2748,10 @@ void QQuickItemPrivate::removeChild(QQuickItem *child)
 
 #ifndef QT_NO_CURSOR
     QQuickItemPrivate *childPrivate = QQuickItemPrivate::get(child);
-    if (childPrivate->extra.isAllocated())
-        incrementCursorCount(-childPrivate->extra.value().numItemsWithCursor);
+
+    // turn it off, if nothing else is using it
+    if (childPrivate->hasCursorInChild && hasCursorInChild)
+        setHasCursorInChild(false);
 #endif
 
     markSortedChildrenDirty(child);
@@ -2948,6 +2953,7 @@ QQuickItemPrivate::QQuickItemPrivate()
     , isAccessible(false)
     , culled(false)
     , hasCursor(false)
+    , hasCursorInChild(false)
     , activeFocusOnTab(false)
     , implicitAntialiasing(false)
     , antialiasingValid(false)
@@ -6731,15 +6737,27 @@ void QQuickItem::setAcceptHoverEvents(bool enabled)
     d->hoverEnabled = enabled;
 }
 
-void QQuickItemPrivate::incrementCursorCount(int delta)
+void QQuickItemPrivate::setHasCursorInChild(bool hasCursor)
 {
 #ifndef QT_NO_CURSOR
     Q_Q(QQuickItem);
-    extra.value().numItemsWithCursor += delta;
+
+    // if we're asked to turn it off (because of an unsetcursor call, or a node
+    // removal) then we should check our children and make sure it's really ok
+    // to turn it off.
+    if (!hasCursor && hasCursorInChild) {
+        foreach (QQuickItem *otherChild, childItems) {
+            QQuickItemPrivate *otherChildPrivate = QQuickItemPrivate::get(otherChild);
+            if (otherChildPrivate->hasCursorInChild)
+                return; // nope! sorry, something else wants it kept on.
+        }
+    }
+
+    hasCursorInChild = hasCursor;
     QQuickItem *parent = q->parentItem();
     if (parent) {
         QQuickItemPrivate *parentPrivate = QQuickItemPrivate::get(parent);
-        parentPrivate->incrementCursorCount(delta);
+        parentPrivate->setHasCursorInChild(hasCursor);
     }
 #endif
 }
@@ -6802,7 +6820,7 @@ void QQuickItem::setCursor(const QCursor &cursor)
     }
 
     if (!d->hasCursor) {
-        d->incrementCursorCount(+1);
+        d->setHasCursorInChild(true);
         d->hasCursor = true;
         if (d->window) {
             QWindow *renderWindow = QQuickRenderControl::renderWindowFor(d->window);
@@ -6825,7 +6843,7 @@ void QQuickItem::unsetCursor()
     Q_D(QQuickItem);
     if (!d->hasCursor)
         return;
-    d->incrementCursorCount(-1);
+    d->setHasCursorInChild(false);
     d->hasCursor = false;
     if (d->extra.isAllocated())
         d->extra->cursor = QCursor();
@@ -7807,9 +7825,6 @@ QQuickItemPrivate::ExtraData::ExtraData()
 : z(0), scale(1), rotation(0), opacity(1),
   contents(0), screenAttached(0), layoutDirectionAttached(0),
   keyHandler(0), layer(0),
-#ifndef QT_NO_CURSOR
-  numItemsWithCursor(0),
-#endif
   effectRefCount(0), hideRefCount(0),
   opacityNode(0), clipNode(0), rootNode(0),
   acceptedMouseButtons(0), origin(QQuickItem::Center),
diff --git a/src/quick/items/qquickitem_p.h b/src/quick/items/qquickitem_p.h
index 2ae67c4c23..461b2f3485 100644
--- a/src/quick/items/qquickitem_p.h
+++ b/src/quick/items/qquickitem_p.h
@@ -342,7 +342,6 @@ public:
         mutable QQuickItemLayer *layer;
 #ifndef QT_NO_CURSOR
         QCursor cursor;
-        int numItemsWithCursor;
 #endif
         QPointF userTransformOriginPoint;
 
@@ -353,6 +352,8 @@ public:
         QQuickDefaultClipNode *clipNode;
         QSGRootNode *rootNode;
 
+        QObjectList resourcesList;
+
         // Although acceptedMouseButtons is inside ExtraData, we actually store
         // the LeftButton flag in the extra.flag() bit.  This is because it is
         // extremely common to set acceptedMouseButtons to LeftButton, but very
@@ -362,7 +363,7 @@ public:
         QQuickItem::TransformOrigin origin:5;
         uint transparentForPositioner : 1;
 
-        QObjectList resourcesList;
+        // 26 bits padding
     };
     QLazilyAllocated<ExtraData> extra;
 
@@ -414,6 +415,7 @@ public:
     bool culled:1;
     bool hasCursor:1;
     // Bit 32
+    bool hasCursorInChild:1;
     bool activeFocusOnTab:1;
     bool implicitAntialiasing:1;
     bool antialiasingValid:1;
@@ -576,7 +578,7 @@ public:
 
     virtual void mirrorChange() {}
 
-    void incrementCursorCount(int delta);
+    void setHasCursorInChild(bool hasCursor);
 
     // recursive helper to let a visual parent mark its visual children
     void markObjects(QV4::ExecutionEngine *e);
diff --git a/src/quick/items/qquickwindow.cpp b/src/quick/items/qquickwindow.cpp
index c7dde6d4aa..8bd6adca94 100644
--- a/src/quick/items/qquickwindow.cpp
+++ b/src/quick/items/qquickwindow.cpp
@@ -2277,10 +2277,7 @@ QQuickItem *QQuickWindowPrivate::findCursorItem(QQuickItem *item, const QPointF
             return 0;
     }
 
-    const int numCursorsInHierarchy = itemPrivate->extra.isAllocated() ? itemPrivate->extra.value().numItemsWithCursor : 0;
-    const int numChildrenWithCursor = itemPrivate->hasCursor ? numCursorsInHierarchy-1 : numCursorsInHierarchy;
-
-    if (numChildrenWithCursor > 0) {
+    if (itemPrivate->hasCursorInChild) {
         QList<QQuickItem *> children = itemPrivate->paintOrderChildItems();
         for (int ii = children.count() - 1; ii >= 0; --ii) {
             QQuickItem *child = children.at(ii);