Add a new optimization flag to QGraphicsItem.

The new flag ItemContainsChildrenInShape is similar to the existing
flag ItemClipsChildrenToShape. Setting the new flag makes QGraphicsScene
assume that children are drawn within the shape of the current item
but this is not enforced by clipping. When an application manually
ensures this clipping boundary, setting the new flag removes the
overhead of enforcing the clip with ItemClipsChildrenToShape, while
still allowing other routines to behave more optimially by assuming
children are within the shape of the current item.

[ChangeLog][QtWidgets][QGraphicsItem] Added the
ItemContainsChildrenInShape flag that enables using optimizations
of ItemClipsChildrenToShape without the overhead of enforcing the clip.

Change-Id: I5496fe1ca331b77fd51e0df8a3ace2b8e939eaf2
Reviewed-by: Andreas Aardal Hanssen <andreas@hanssen.name>

1 files changed, 16 insertions, 8 deletions

diff --git a/src/widgets/graphicsview/qgraphicsscenebsptreeindex.cpp b/src/widgets/graphicsview/qgraphicsscenebsptreeindex.cpp
index 7598163f2d..50f17ab73f 100644
--- a/src/widgets/graphicsview/qgraphicsscenebsptreeindex.cpp
+++ b/src/widgets/graphicsview/qgraphicsscenebsptreeindex.cpp
@@ -169,7 +169,8 @@ void QGraphicsSceneBspTreeIndexPrivate::_q_updateIndex()
                 untransformableItems << item;
                 continue;
             }
-            if (item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren)
+            if (item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren
+                || item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorContainsChildren)
                 continue;
 
             bsp.insertItem(item, item->d_ptr->sceneEffectiveBoundingRect());
@@ -351,7 +352,8 @@ void QGraphicsSceneBspTreeIndexPrivate::removeItem(QGraphicsItem *item, bool rec
             // Avoid virtual function calls from the destructor.
             purgePending = true;
             removedItems << item;
-        } else if (!(item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren)) {
+        } else if (!(item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren
+                     || item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorContainsChildren)) {
             bsp.removeItem(item, item->d_ptr->sceneEffectiveBoundingRect());
         }
     } else {
@@ -510,7 +512,8 @@ void QGraphicsSceneBspTreeIndex::prepareBoundingRectChange(const QGraphicsItem *
         return;
 
     if (item->d_ptr->index == -1 || item->d_ptr->itemIsUntransformable()
-        || (item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren)) {
+        || (item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren
+            || item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorContainsChildren)) {
         return; // Item is not in BSP tree; nothing to do.
     }
 
@@ -641,8 +644,10 @@ void QGraphicsSceneBspTreeIndex::itemChange(const QGraphicsItem *item, QGraphics
         QGraphicsItem::GraphicsItemFlags newFlags = *static_cast<const QGraphicsItem::GraphicsItemFlags *>(value);
         bool ignoredTransform = item->d_ptr->flags & QGraphicsItem::ItemIgnoresTransformations;
         bool willIgnoreTransform = newFlags & QGraphicsItem::ItemIgnoresTransformations;
-        bool clipsChildren = item->d_ptr->flags & QGraphicsItem::ItemClipsChildrenToShape;
-        bool willClipChildren = newFlags & QGraphicsItem::ItemClipsChildrenToShape;
+        bool clipsChildren = item->d_ptr->flags & QGraphicsItem::ItemClipsChildrenToShape
+                             || item->d_ptr->flags & QGraphicsItem::ItemContainsChildrenInShape;
+        bool willClipChildren = newFlags & QGraphicsItem::ItemClipsChildrenToShape
+                                || newFlags & QGraphicsItem::ItemContainsChildrenInShape;
         if ((ignoredTransform != willIgnoreTransform) || (clipsChildren != willClipChildren)) {
             QGraphicsItem *thatItem = const_cast<QGraphicsItem *>(item);
             // Remove item and its descendants from the index and append
@@ -663,10 +668,13 @@ void QGraphicsSceneBspTreeIndex::itemChange(const QGraphicsItem *item, QGraphics
         bool ignoredTransform = item->d_ptr->itemIsUntransformable();
         bool willIgnoreTransform = (item->d_ptr->flags & QGraphicsItem::ItemIgnoresTransformations)
                                    || (newParent && newParent->d_ptr->itemIsUntransformable());
-        bool ancestorClippedChildren = item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren;
+        bool ancestorClippedChildren = item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren
+                                       || item->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorContainsChildren;
         bool ancestorWillClipChildren = newParent
-                            && ((newParent->d_ptr->flags & QGraphicsItem::ItemClipsChildrenToShape)
-                                || (newParent->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren));
+                            && ((newParent->d_ptr->flags & QGraphicsItem::ItemClipsChildrenToShape
+                                 || newParent->d_ptr->flags & QGraphicsItem::ItemContainsChildrenInShape)
+                                || (newParent->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorClipsChildren
+                                    || newParent->d_ptr->ancestorFlags & QGraphicsItemPrivate::AncestorContainsChildren));
         if ((ignoredTransform != willIgnoreTransform) || (ancestorClippedChildren != ancestorWillClipChildren)) {
             QGraphicsItem *thatItem = const_cast<QGraphicsItem *>(item);
             // Remove item and its descendants from the index and append