Fixes: Discard update requests if possible.

AutoTest: Still pass.
Details:  Update requests can be discarded if the item itself is
          clipped away and the item clips all its children to shape.

          This cut-off is extremely effective (and aggressive:))

2 files changed, 35 insertions, 10 deletions

diff --git a/src/gui/graphicsview/qgraphicsitem.cpp b/src/gui/graphicsview/qgraphicsitem.cpp
index 327b352..23787a7 100644
--- a/src/gui/graphicsview/qgraphicsitem.cpp
+++ b/src/gui/graphicsview/qgraphicsitem.cpp
@@ -1102,10 +1102,7 @@ void QGraphicsItem::setParentItem(QGraphicsItem *parent)
     }
 
     // Resolve opacity.
-    if (QGraphicsItem *p = d_ptr->parent)
-        d_ptr->resolveEffectiveOpacity(p->effectiveOpacity());
-    else
-        d_ptr->resolveEffectiveOpacity(1.0);
+    d_ptr->updateEffectiveOpacity();
 
     // Resolve depth.
     d_ptr->resolveDepth(parent ? parent->d_ptr->depth : -1);
@@ -1246,12 +1243,8 @@ void QGraphicsItem::setFlags(GraphicsItemFlags flags)
 
     // Reresolve effective opacity if the opacity flags change.
     static const quint32 opacityFlagsMask = ItemIgnoresParentOpacity | ItemDoesntPropagateOpacityToChildren;
-    if ((flags & opacityFlagsMask) != (oldFlags & opacityFlagsMask)) {
-        if (QGraphicsItem *p = d_ptr->parent)
-            d_ptr->resolveEffectiveOpacity(p->effectiveOpacity());
-        else
-            d_ptr->resolveEffectiveOpacity(1.0);
-    }
+    if ((flags & opacityFlagsMask) != (oldFlags & opacityFlagsMask))
+        d_ptr->updateEffectiveOpacity();
 
     if (!(d_ptr->flags & ItemIsFocusable) && hasFocus()) {
         // Clear focus on the item if it has focus when the focusable flag
@@ -3693,6 +3686,32 @@ void QGraphicsItemPrivate::fullUpdateHelper(bool childrenOnly, bool maybeDirtyCl
     dirtyChildren = 1;
 }
 
+static inline bool allChildrenCombineOpacity(QGraphicsItem *parent)
+{
+    Q_ASSERT(parent);
+    if (parent->flags() & QGraphicsItem::ItemDoesntPropagateOpacityToChildren)
+        return false;
+
+    const QList<QGraphicsItem *> children(parent->childItems());
+    for (int i = 0; i < children.size(); ++i) {
+        if (children.at(i)->flags() & QGraphicsItem::ItemIgnoresParentOpacity)
+            return false;
+    }
+    return true;
+}
+
+void QGraphicsItemPrivate::updateEffectiveOpacity()
+{
+    Q_Q(QGraphicsItem);
+    if (parent) {
+        resolveEffectiveOpacity(parent->effectiveOpacity());
+        parent->d_ptr->allChildrenCombineOpacity = ::allChildrenCombineOpacity(parent);
+    } else {
+        resolveEffectiveOpacity(1.0);
+    }
+    allChildrenCombineOpacity = ::allChildrenCombineOpacity(q);
+}
+
 /*!
     \internal
 
diff --git a/src/gui/graphicsview/qgraphicsitem_p.h b/src/gui/graphicsview/qgraphicsitem_p.h
index dabbe53..c795915 100644
--- a/src/gui/graphicsview/qgraphicsitem_p.h
+++ b/src/gui/graphicsview/qgraphicsitem_p.h
@@ -141,6 +141,7 @@ public:
         dirtyClipPath(1),
         emptyClipPath(0),
         inSetPosHelper(0),
+        allChildrenCombineOpacity(1),
         globalStackingOrder(-1),
         sceneTransformIndex(-1),
         q_ptr(0)
@@ -166,6 +167,7 @@ public:
     void setEnabledHelper(bool newEnabled, bool explicitly, bool update = true);
     void updateHelper(const QRectF &rect = QRectF(), bool force = false, bool maybeDirtyClipPath = false);
     void fullUpdateHelper(bool childrenOnly = false, bool maybeDirtyClipPath = false);
+    void updateEffectiveOpacity();
     void resolveEffectiveOpacity(qreal effectiveParentOpacity);
     void resolveDepth(int parentDepth);
     void invalidateSceneTransformCache();
@@ -264,6 +266,9 @@ public:
                             && qFuzzyCompare(q_func()->effectiveOpacity() + 1, qreal(1.0)));
     }
 
+    inline bool childrenCombineOpacity() const
+    { return allChildrenCombineOpacity || children.isEmpty(); }
+
     inline bool isClippedAway() const
     { return !dirtyClipPath && q_func()->isClipped() && (emptyClipPath || cachedClipPath.isEmpty()); }
 
@@ -308,6 +313,7 @@ public:
     quint32 dirtyClipPath : 1;
     quint32 emptyClipPath : 1;
     quint32 inSetPosHelper : 1;
+    quint32 allChildrenCombineOpacity : 1;
 
     // Optional stacking order
     int globalStackingOrder;