Graphics View Optimization: Use a simple style option by default.

QStyleOptionGraphicsItem extends QStyleOption with three values:
1) matrix, 2) levelOfDetail, 3) exposedRect, and they all
involve expensive QTranform operations when calculated. We
pass style option(s) to drawItems() and paint(), but the
extended values are usually not in use. We can therefore gain
quite some nice speedup by making them opt-in with the
QGraphicsItem::ItemUsesExtendedStyleOption flag.

Additionally, QStyleOptionGraphicsItem::levelOfDetail has been
obsoleted, and a new function QStyleOptionGraphicsItem::
levelOfDetailFromTransform(const QTransform &) has been added.

Me and Andreas don't consider this change to be too controversial
even though it changes the behavior.

Auto tests still pass.

Reviewed-by: Andreas

13 files changed, 155 insertions, 180 deletions

diff --git a/demos/chip/chip.cpp b/demos/chip/chip.cpp
index c2b22dad8b..4b6579e7e5 100644
--- a/demos/chip/chip.cpp
+++ b/demos/chip/chip.cpp
@@ -74,8 +74,9 @@ void Chip::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWid
     if (option->state & QStyle::State_MouseOver)
         fillColor = fillColor.light(125);
 
-    if (option->levelOfDetail < 0.2) {
-        if (option->levelOfDetail < 0.125) {
+    const qreal lod = option->levelOfDetailFromTransform(painter->worldTransform());
+    if (lod < 0.2) {
+        if (lod < 0.125) {
             painter->fillRect(QRectF(0, 0, 110, 70), fillColor);
             return;
         }
@@ -100,7 +101,7 @@ void Chip::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWid
     painter->drawRect(QRect(14, 14, 79, 39));
     painter->setBrush(b);
 
-    if (option->levelOfDetail >= 1) {
+    if (lod >= 1) {
         painter->setPen(QPen(Qt::gray, 1));
         painter->drawLine(15, 54, 94, 54);
         painter->drawLine(94, 53, 94, 15);
@@ -108,7 +109,7 @@ void Chip::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWid
     }
 
     // Draw text
-    if (option->levelOfDetail >= 2) {
+    if (lod >= 2) {
         QFont font("Times", 10);
         font.setStyleStrategy(QFont::ForceOutline);
         painter->setFont(font);
@@ -122,17 +123,17 @@ void Chip::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWid
 
     // Draw lines
     QVarLengthArray<QLineF, 36> lines;
-    if (option->levelOfDetail >= 0.5) {
-        for (int i = 0; i <= 10; i += (option->levelOfDetail > 0.5 ? 1 : 2)) {
+    if (lod >= 0.5) {
+        for (int i = 0; i <= 10; i += (lod > 0.5 ? 1 : 2)) {
             lines.append(QLineF(18 + 7 * i, 13, 18 + 7 * i, 5));
             lines.append(QLineF(18 + 7 * i, 54, 18 + 7 * i, 62));
         }
-        for (int i = 0; i <= 6; i += (option->levelOfDetail > 0.5 ? 1 : 2)) {
+        for (int i = 0; i <= 6; i += (lod > 0.5 ? 1 : 2)) {
             lines.append(QLineF(5, 18 + i * 5, 13, 18 + i * 5));
             lines.append(QLineF(94, 18 + i * 5, 102, 18 + i * 5));
         }
     }
-    if (option->levelOfDetail >= 0.4) {
+    if (lod >= 0.4) {
         const QLineF lineData[] = {
             QLineF(25, 35, 35, 35),
             QLineF(35, 30, 35, 40),
diff --git a/dist/changes-4.6.0 b/dist/changes-4.6.0
index db4ab5f104..6a94f26fa6 100644
--- a/dist/changes-4.6.0
+++ b/dist/changes-4.6.0
@@ -38,4 +38,14 @@ information about a particular change.
 
  - The experimental Direct3D paint engine has been removed. The
    reasons for this is that Qt Software focuses on OpenGL for desktop
-   hardware accelerated rendering.
\ No newline at end of file
+   hardware accelerated rendering.
+
+ - QStyleOptionGraphicsItem::exposedRect and QStyleOptionGraphicsItem::matrix
+   does no longer contain fine-grained values when passed in drawItems()/paint()
+   unless the QGraphicsItem::ItemUsesExtendedStyleOptions flag is enabled.
+   By default, exposedRect is initialized to the item's bounding rect
+   and the matrix is untransformed.
+
+ - QStyleOptionGraphicsItem::levelOfDetails is obsoleted and its value
+   is always initialized to 1. For a more fine-grained value use
+   QStyleOptionGraphicsItem::levelOfDetailFromTransform(const QTransform &).
diff --git a/src/gui/graphicsview/qgraphicsitem.cpp b/src/gui/graphicsview/qgraphicsitem.cpp
index aa55908695..ec08aaf442 100644
--- a/src/gui/graphicsview/qgraphicsitem.cpp
+++ b/src/gui/graphicsview/qgraphicsitem.cpp
@@ -274,6 +274,15 @@
     this flag, the child will be stacked behind it. This flag is useful for
     drop shadow effects and for decoration objects that follow the parent
     item's geometry without drawing on top of it.
+
+    \value ItemUsesExtendedStyleOption The item makes use of either
+    QStyleOptionGraphicsItem::exposedRect or QStyleOptionGraphicsItem::matrix.
+    By default, the exposedRect is initialized to the item's boundingRect and
+    the matrix is untransformed. Enable this flag for more fine-grained values.
+    Note that QStyleOptionGraphicsItem::levelOfDetail is unaffected by this flag
+    and is always initialized to 1.
+    Use QStyleOptionGraphicsItem::levelOfDetailFromTransform for a more
+    fine-grained value.
 */
 
 /*!
@@ -914,6 +923,53 @@ void QGraphicsItemPrivate::childrenBoundingRectHelper(QTransform *x, QRectF *rec
     }
 }
 
+void QGraphicsItemPrivate::initStyleOption(QStyleOptionGraphicsItem *option, const QTransform &worldTransform,
+                                           const QRegion &exposedRegion, bool allItems) const
+{
+    Q_ASSERT(option);
+    Q_Q(const QGraphicsItem);
+
+    // Initialize standard QStyleOption values.
+    const QRectF brect = q->boundingRect();
+    option->state = QStyle::State_None;
+    option->rect = brect.toRect();
+    option->levelOfDetail = 1;
+    option->exposedRect = brect;
+    if (selected)
+        option->state |= QStyle::State_Selected;
+    if (enabled)
+        option->state |= QStyle::State_Enabled;
+    if (q->hasFocus())
+        option->state |= QStyle::State_HasFocus;
+    if (scene) {
+        if (scene->d_func()->hoverItems.contains(q_ptr))
+            option->state |= QStyle::State_MouseOver;
+        if (q == scene->mouseGrabberItem())
+            option->state |= QStyle::State_Sunken;
+    }
+
+    if (!(flags & QGraphicsItem::ItemUsesExtendedStyleOption))
+        return;
+
+    // Initialize QStyleOptionGraphicsItem specific values (matrix, exposedRect).
+
+    const QTransform itemToViewportTransform = q->deviceTransform(worldTransform);
+    option->matrix = itemToViewportTransform.toAffine(); //### discards perspective
+
+    if (!allItems) {
+        // Determine the item's exposed area
+        option->exposedRect = QRectF();
+        const QTransform reverseMap = itemToViewportTransform.inverted();
+        const QVector<QRect> exposedRects(exposedRegion.rects());
+        for (int i = 0; i < exposedRects.size(); ++i) {
+            option->exposedRect |= reverseMap.mapRect(exposedRects.at(i));
+            if (option->exposedRect.contains(brect))
+                break;
+        }
+        option->exposedRect &= brect;
+    }
+}
+
 /*!
     \internal
 
@@ -3671,7 +3727,7 @@ void QGraphicsItem::setBoundingRegionGranularity(qreal granularity)
 
     All painting is done in local coordinates.
 
-    \sa setCacheMode(), QPen::width(), {Item Coordinates}
+    \sa setCacheMode(), QPen::width(), {Item Coordinates}, ItemUsesExtendedStyleOption
 */
 
 /*!
@@ -7635,9 +7691,7 @@ void QGraphicsPixmapItem::paint(QPainter *painter, const QStyleOptionGraphicsIte
     painter->setRenderHint(QPainter::SmoothPixmapTransform,
                            (d->transformationMode == Qt::SmoothTransformation));
 
-    QRectF exposed = option->exposedRect.adjusted(-1, -1, 1, 1);
-    exposed &= QRectF(d->offset.x(), d->offset.y(), d->pixmap.width(), d->pixmap.height());
-    painter->drawPixmap(exposed, d->pixmap, exposed.translated(-d->offset));
+    painter->drawPixmap(d->offset, d->pixmap);
 
     if (option->state & QStyle::State_Selected)
         qt_graphicsItem_highlightSelected(this, painter, option);
@@ -7803,6 +7857,7 @@ QGraphicsTextItem::QGraphicsTextItem(const QString &text, QGraphicsItem *parent
         setPlainText(text);
     setAcceptDrops(true);
     setAcceptHoverEvents(true);
+    setFlags(ItemUsesExtendedStyleOption);
 }
 
 /*!
@@ -7822,6 +7877,7 @@ QGraphicsTextItem::QGraphicsTextItem(QGraphicsItem *parent
     dd->qq = this;
     setAcceptDrops(true);
     setAcceptHoverEvents(true);
+    setFlag(ItemUsesExtendedStyleOption);
 }
 
 /*!
@@ -9167,6 +9223,9 @@ QDebug operator<<(QDebug debug, QGraphicsItem::GraphicsItemFlag flag)
     case QGraphicsItem::ItemStacksBehindParent:
         str = "ItemStacksBehindParent";
         break;
+    case QGraphicsItem::ItemUsesExtendedStyleOption:
+        str = "ItemUsesExtendedStyleOption";
+        break;
     }
     debug << str;
     return debug;
diff --git a/src/gui/graphicsview/qgraphicsitem.h b/src/gui/graphicsview/qgraphicsitem.h
index b98882d1d4..0a0179ebab 100644
--- a/src/gui/graphicsview/qgraphicsitem.h
+++ b/src/gui/graphicsview/qgraphicsitem.h
@@ -94,7 +94,9 @@ public:
         ItemIgnoresTransformations = 0x20,
         ItemIgnoresParentOpacity = 0x40,
         ItemDoesntPropagateOpacityToChildren = 0x80,
-        ItemStacksBehindParent = 0x100
+        ItemStacksBehindParent = 0x100,
+        ItemUsesExtendedStyleOption = 0x200
+        // NB! Don't forget to increase the d_ptr->flags bit field by 1 when adding a new flag.
     };
     Q_DECLARE_FLAGS(GraphicsItemFlags, GraphicsItemFlag)
 
diff --git a/src/gui/graphicsview/qgraphicsitem_p.h b/src/gui/graphicsview/qgraphicsitem_p.h
index 2936cf1d65..82a48fb789 100644
--- a/src/gui/graphicsview/qgraphicsitem_p.h
+++ b/src/gui/graphicsview/qgraphicsitem_p.h
@@ -132,7 +132,6 @@ public:
         ancestorFlags(0),
         cacheMode(0),
         hasBoundingRegionGranularity(0),
-        flags(0),
         hasOpacity(0),
         hasEffectiveOpacity(0),
         isWidget(0),
@@ -142,6 +141,7 @@ public:
         dirtyClipPath(1),
         emptyClipPath(0),
         inSetPosHelper(0),
+        flags(0),
         allChildrenCombineOpacity(1),
         globalStackingOrder(-1),
         sceneTransformIndex(-1),
@@ -178,6 +178,8 @@ public:
     void removeChild(QGraphicsItem *child);
     void setParentItemHelper(QGraphicsItem *parent, bool deleting);
     void childrenBoundingRectHelper(QTransform *x, QRectF *rect);
+    void initStyleOption(QStyleOptionGraphicsItem *option, const QTransform &worldTransform,
+                         const QRegion &exposedRegion, bool allItems = false) const;
 
     virtual void resolveFont(uint inheritedMask)
     {
@@ -297,7 +299,7 @@ public:
     int index;
     int depth;
 
-    // Packed 32 bytes
+    // Packed 32 bits
     quint32 acceptedMouseButtons : 5;
     quint32 visible : 1;
     quint32 explicitlyHidden : 1;
@@ -314,9 +316,6 @@ public:
     quint32 ancestorFlags : 3;
     quint32 cacheMode : 2;
     quint32 hasBoundingRegionGranularity : 1;
-    quint32 flags : 9;
-
-    // New 32 bytes
     quint32 hasOpacity : 1;
     quint32 hasEffectiveOpacity : 1;
     quint32 isWidget : 1;
@@ -326,7 +325,11 @@ public:
     quint32 dirtyClipPath : 1;
     quint32 emptyClipPath : 1;
     quint32 inSetPosHelper : 1;
+
+    // New 32 bits
+    quint32 flags : 10;
     quint32 allChildrenCombineOpacity : 1;
+    quint32 padding : 21; // feel free to use
 
     // Optional stacking order
     int globalStackingOrder;
diff --git a/src/gui/graphicsview/qgraphicsscene.cpp b/src/gui/graphicsview/qgraphicsscene.cpp
index c421f05b38..7318fa5f59 100644
--- a/src/gui/graphicsview/qgraphicsscene.cpp
+++ b/src/gui/graphicsview/qgraphicsscene.cpp
@@ -2247,8 +2247,6 @@ void QGraphicsScene::setSceneRect(const QRectF &rect)
 void QGraphicsScene::render(QPainter *painter, const QRectF &target, const QRectF &source,
                             Qt::AspectRatioMode aspectRatioMode)
 {
-    Q_D(QGraphicsScene);
-
     // Default source rect = scene rect
     QRectF sourceRect = source;
     if (sourceRect.isNull())
@@ -2305,36 +2303,8 @@ void QGraphicsScene::render(QPainter *painter, const QRectF &target, const QRect
 
     // Generate the style options
     QStyleOptionGraphicsItem *styleOptionArray = new QStyleOptionGraphicsItem[numItems];
-    for (int i = 0; i < numItems; ++i) {
-        QGraphicsItem *item = itemArray[i];
-
-        QStyleOptionGraphicsItem option;
-        option.state = QStyle::State_None;
-        option.rect = item->boundingRect().toRect();
-        if (item->isSelected())
-            option.state |= QStyle::State_Selected;
-        if (item->isEnabled())
-            option.state |= QStyle::State_Enabled;
-        if (item->hasFocus())
-            option.state |= QStyle::State_HasFocus;
-        if (d->hoverItems.contains(item))
-            option.state |= QStyle::State_MouseOver;
-        if (item == mouseGrabberItem())
-            option.state |= QStyle::State_Sunken;
-
-        // Calculate a simple level-of-detail metric.
-        // ### almost identical code in QGraphicsView::paintEvent()
-        //     and QGraphicsView::render() - consider refactoring
-        QTransform itemToDeviceTransform = item->deviceTransform(painterTransform);
-
-        option.levelOfDetail = qSqrt(itemToDeviceTransform.map(v1).length() * itemToDeviceTransform.map(v2).length());
-        option.matrix = itemToDeviceTransform.toAffine(); //### discards perspective
-
-        option.exposedRect = item->boundingRect();
-        option.exposedRect &= itemToDeviceTransform.inverted().mapRect(targetRect);
-
-        styleOptionArray[i] = option;
-    }
+    for (int i = 0; i < numItems; ++i)
+        itemArray[i]->d_ptr->initStyleOption(&styleOptionArray[i], painterTransform, targetRect.toRect());
 
     // Render the scene.
     drawBackground(painter, sourceRect);
diff --git a/src/gui/graphicsview/qgraphicsview.cpp b/src/gui/graphicsview/qgraphicsview.cpp
index 71810451d3..396618c942 100644
--- a/src/gui/graphicsview/qgraphicsview.cpp
+++ b/src/gui/graphicsview/qgraphicsview.cpp
@@ -1127,69 +1127,6 @@ QList<QGraphicsItem *> QGraphicsViewPrivate::findItems(const QRegion &exposedReg
     return itemsInArea(exposedPath, Qt::IntersectsItemBoundingRect, Qt::DescendingOrder);
 }
 
-void QGraphicsViewPrivate::generateStyleOptions(const QList<QGraphicsItem *> &itemList,
-                                                QGraphicsItem **itemArray,
-                                                QStyleOptionGraphicsItem *styleOptionArray,
-                                                const QTransform &worldTransform,
-                                                bool allItems,
-                                                const QRegion &exposedRegion) const
-{
-    // Two unit vectors.
-    QLineF v1(0, 0, 1, 0);
-    QLineF v2(0, 0, 0, 1);
-    QTransform itemToViewportTransform;
-    QRectF brect;
-    QTransform reverseMap;
-
-    for (int i = 0; i < itemList.size(); ++i) {
-        QGraphicsItem *item = itemArray[i] = itemList[i];
-
-        QStyleOptionGraphicsItem &option = styleOptionArray[i];
-        brect = item->boundingRect();
-        option.state = QStyle::State_None;
-        option.rect = brect.toRect();
-        option.exposedRect = QRectF();
-        if (item->d_ptr->selected)
-            option.state |= QStyle::State_Selected;
-        if (item->d_ptr->enabled)
-            option.state |= QStyle::State_Enabled;
-        if (item->hasFocus())
-            option.state |= QStyle::State_HasFocus;
-        if (scene->d_func()->hoverItems.contains(item))
-            option.state |= QStyle::State_MouseOver;
-        if (item == scene->mouseGrabberItem())
-            option.state |= QStyle::State_Sunken;
-
-        // Calculate a simple level-of-detail metric.
-        // ### almost identical code in QGraphicsScene::render()
-        //     and QGraphicsView::render() - consider refactoring
-        itemToViewportTransform = item->deviceTransform(worldTransform);
-
-        if (itemToViewportTransform.type() <= QTransform::TxTranslate) {
-            // Translation and rotation only? The LOD is 1.
-            option.levelOfDetail = 1;
-        } else {
-            // LOD is the transformed area of a 1x1 rectangle.
-            option.levelOfDetail = qSqrt(itemToViewportTransform.map(v1).length() * itemToViewportTransform.map(v2).length());
-        }
-        option.matrix = itemToViewportTransform.toAffine(); //### discards perspective
-
-        if (!allItems) {
-            // Determine the item's exposed area
-            reverseMap = itemToViewportTransform.inverted();
-            foreach (const QRect &rect, exposedRegion.rects()) {
-                option.exposedRect |= reverseMap.mapRect(QRectF(rect.adjusted(-1, -1, 1, 1)));
-                if (option.exposedRect.contains(brect))
-                    break;
-            }
-            option.exposedRect &= brect;
-        } else {
-            // The whole item is exposed
-            option.exposedRect = brect;
-        }
-    }
-}
-
 /*!
     Constructs a QGraphicsView. \a parent is passed to QWidget's constructor.
 */
@@ -2146,40 +2083,10 @@ void QGraphicsView::render(QPainter *painter, const QRectF &target, const QRect
                      .scale(xratio, yratio)
                      .translate(-sourceRect.left(), -sourceRect.top());
 
-    // Two unit vectors.
-    QLineF v1(0, 0, 1, 0);
-    QLineF v2(0, 0, 0, 1);
-
     // Generate the style options
     QStyleOptionGraphicsItem *styleOptionArray = d->allocStyleOptionsArray(numItems);
-    QStyleOptionGraphicsItem* option = styleOptionArray;
-    for (int i = 0; i < numItems; ++i, ++option) {
-        QGraphicsItem *item = itemArray[i];
-
-        option->state = QStyle::State_None;
-        option->rect = item->boundingRect().toRect();
-        if (item->isSelected())
-            option->state |= QStyle::State_Selected;
-        if (item->isEnabled())
-            option->state |= QStyle::State_Enabled;
-        if (item->hasFocus())
-            option->state |= QStyle::State_HasFocus;
-        if (d->scene->d_func()->hoverItems.contains(item))
-            option->state |= QStyle::State_MouseOver;
-        if (item == d->scene->mouseGrabberItem())
-            option->state |= QStyle::State_Sunken;
-
-        // Calculate a simple level-of-detail metric.
-        // ### almost identical code in QGraphicsScene::render()
-        //     and QGraphicsView::paintEvent() - consider refactoring
-        QTransform itemToViewportTransform = item->deviceTransform(painterMatrix);
-
-        option->levelOfDetail = qSqrt(itemToViewportTransform.map(v1).length() * itemToViewportTransform.map(v2).length());
-        option->matrix = itemToViewportTransform.toAffine();
-
-        option->exposedRect = item->boundingRect();
-        option->exposedRect &= itemToViewportTransform.inverted().mapRect(targetRect);
-    }
+    for (int i = 0; i < numItems; ++i)
+        itemArray[i]->d_ptr->initStyleOption(&styleOptionArray[i], painterMatrix, targetRect.toRect());
 
     painter->save();
 
@@ -3538,15 +3445,17 @@ void QGraphicsView::paintEvent(QPaintEvent *event)
     int backgroundTime = stopWatch.elapsed() - exposedTime;
 #endif
 
-    // Generate the style options
-    QGraphicsItem **itemArray = new QGraphicsItem *[itemList.size()];
-    QStyleOptionGraphicsItem *styleOptionArray = d->allocStyleOptionsArray(itemList.size());
-
-    d->generateStyleOptions(itemList, itemArray, styleOptionArray, viewTransform,
-                            allItems, exposedRegion);
-
-    // Items
-    drawItems(&painter, itemList.size(), itemArray, styleOptionArray);
+    if (!itemList.isEmpty()) {
+        // Generate the style options.
+        const int numItems = itemList.size();
+        QGraphicsItem **itemArray = &itemList[0]; // Relies on QList internals, but is perfectly valid.
+        QStyleOptionGraphicsItem *styleOptionArray = d->allocStyleOptionsArray(numItems);
+        for (int i = 0; i < numItems; ++i)
+            itemArray[i]->d_ptr->initStyleOption(&styleOptionArray[i], viewTransform, exposedRegion, allItems);
+        // Draw the items.
+        drawItems(&painter, numItems, itemArray, styleOptionArray);
+        d->freeStyleOptionsArray(styleOptionArray);
+    }
 
 #ifdef QGRAPHICSVIEW_DEBUG
     int itemsTime = stopWatch.elapsed() - exposedTime - backgroundTime;
@@ -3555,9 +3464,6 @@ void QGraphicsView::paintEvent(QPaintEvent *event)
     // Foreground
     drawForeground(&painter, exposedSceneRect);
 
-    delete [] itemArray;
-    d->freeStyleOptionsArray(styleOptionArray);
-
 #ifdef QGRAPHICSVIEW_DEBUG
     int foregroundTime = stopWatch.elapsed() - exposedTime - backgroundTime - itemsTime;
 #endif
diff --git a/src/gui/graphicsview/qgraphicsview_p.h b/src/gui/graphicsview/qgraphicsview_p.h
index d573e8f548..c18f85daef 100644
--- a/src/gui/graphicsview/qgraphicsview_p.h
+++ b/src/gui/graphicsview/qgraphicsview_p.h
@@ -174,13 +174,6 @@ public:
     bool updateSceneSlotReimplementedChecked;
 
     QList<QGraphicsItem *> findItems(const QRegion &exposedRegion, bool *allItems) const;
-
-    void generateStyleOptions(const QList<QGraphicsItem *> &itemList,
-			      QGraphicsItem **itemArray,
-			      QStyleOptionGraphicsItem *styleOptionArray,
-			      const QTransform &worldTransform,
-			      bool allItems,
-			      const QRegion &exposedRegion) const;
 };
 
 QT_END_NAMESPACE
diff --git a/src/gui/graphicsview/qgraphicswidget_p.cpp b/src/gui/graphicsview/qgraphicswidget_p.cpp
index 8ced47ab20..a435758612 100644
--- a/src/gui/graphicsview/qgraphicswidget_p.cpp
+++ b/src/gui/graphicsview/qgraphicswidget_p.cpp
@@ -76,6 +76,7 @@ void QGraphicsWidgetPrivate::init(QGraphicsItem *parentItem, Qt::WindowFlags wFl
 
     resolveLayoutDirection();
     q->unsetWindowFrameMargins();
+    q->setFlag(QGraphicsItem::ItemUsesExtendedStyleOption);
 }
 qreal QGraphicsWidgetPrivate::titleBarHeight(const QStyleOptionTitleBar &options) const
 {
diff --git a/src/gui/styles/qstyleoption.cpp b/src/gui/styles/qstyleoption.cpp
index ce053aef31..5b1bc617ad 100644
--- a/src/gui/styles/qstyleoption.cpp
+++ b/src/gui/styles/qstyleoption.cpp
@@ -48,6 +48,7 @@
 #ifndef QT_NO_DEBUG
 #include <qdebug.h>
 #endif
+#include <QtCore/qmath.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -4998,6 +4999,34 @@ QStyleOptionGraphicsItem::QStyleOptionGraphicsItem(int version)
 }
 
 /*!
+    \since 4.6
+
+    Returns the level of detail from the \a worldTransform.
+
+    Its value represents the maximum value of the height and
+    width of a unity rectangle, mapped using the \a worldTransform
+    of the painter used to draw the item. By default, if no
+    transformations are applied, its value is 1. If zoomed out 1:2, the level
+    of detail will be 0.5, and if zoomed in 2:1, its value is 2.
+
+    For more advanced level-of-detail metrics, use
+    QStyleOptionGraphicsItem::matrix directly.
+
+    \sa QStyleOptionGraphicsItem::matrix
+*/
+qreal QStyleOptionGraphicsItem::levelOfDetailFromTransform(const QTransform &worldTransform)
+{
+    if (worldTransform.type() <= QTransform::TxTranslate)
+        return 1; // Translation only? The LOD is 1.
+
+    // Two unit vectors.
+    QLineF v1(0, 0, 1, 0);
+    QLineF v2(0, 0, 0, 1);
+    // LOD is the transformed area of a 1x1 rectangle.
+    return qSqrt(worldTransform.map(v1).length() * worldTransform.map(v2).length());
+}
+
+/*!
     \fn QStyleOptionGraphicsItem::QStyleOptionGraphicsItem(const QStyleOptionGraphicsItem &other)
 
     Constructs a copy of \a other.
@@ -5029,19 +5058,10 @@ QStyleOptionGraphicsItem::QStyleOptionGraphicsItem(int version)
 
 /*!
     \variable QStyleOptionGraphicsItem::levelOfDetail
-    \brief a simple metric for determining an item's level of detail
-
-    This simple metric provides an easy way to determine the level of detail
-    for an item. Its value represents the maximum value of the height and
-    width of a unity rectangle, mapped using the complete transformation
-    matrix of the painter used to draw the item. By default, if no
-    transformations are applied, its value is 1. If zoomed out 1:2, the level
-    of detail will be 0.5, and if zoomed in 2:1, its value is 2.
-
-    For more advanced level-of-detail metrics, use
-    QStyleOptionGraphicsItem::matrix directly.
+    \obsolete
 
-    \sa QStyleOptionGraphicsItem::matrix
+    Use QStyleOptionGraphicsItem::levelOfDetailFromTransform
+    together with QPainter::worldTransform() instead.
 */
 
 /*!
diff --git a/src/gui/styles/qstyleoption.h b/src/gui/styles/qstyleoption.h
index 5759a054a2..eb05324ff3 100644
--- a/src/gui/styles/qstyleoption.h
+++ b/src/gui/styles/qstyleoption.h
@@ -856,6 +856,7 @@ public:
 
     QStyleOptionGraphicsItem();
     QStyleOptionGraphicsItem(const QStyleOptionGraphicsItem &other) : QStyleOption(Version, Type) { *this = other; }
+    static qreal levelOfDetailFromTransform(const QTransform &worldTransform);
 protected:
     QStyleOptionGraphicsItem(int version);
 };
diff --git a/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp b/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp
index 8602307910..b3ae60a9c2 100644
--- a/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp
+++ b/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp
@@ -247,50 +247,59 @@ void tst_QGraphicsItem::construction()
             QCOMPARE(int(item->type()), int(QGraphicsEllipseItem::Type));
             QCOMPARE(qgraphicsitem_cast<QGraphicsEllipseItem *>(item), (QGraphicsEllipseItem *)item);
             QCOMPARE(qgraphicsitem_cast<QGraphicsRectItem *>(item), (QGraphicsRectItem *)0);
+            QCOMPARE(item->flags(), 0);
             break;
         case 1:
             item = new QGraphicsLineItem;
             QCOMPARE(int(item->type()), int(QGraphicsLineItem::Type));
             QCOMPARE(qgraphicsitem_cast<QGraphicsLineItem *>(item), (QGraphicsLineItem *)item);
             QCOMPARE(qgraphicsitem_cast<QGraphicsRectItem *>(item), (QGraphicsRectItem *)0);
+            QCOMPARE(item->flags(), 0);
             break;
         case 2:
             item = new QGraphicsPathItem;
             QCOMPARE(int(item->type()), int(QGraphicsPathItem::Type));
             QCOMPARE(qgraphicsitem_cast<QGraphicsPathItem *>(item), (QGraphicsPathItem *)item);
             QCOMPARE(qgraphicsitem_cast<QGraphicsRectItem *>(item), (QGraphicsRectItem *)0);
+            QCOMPARE(item->flags(), 0);
             break;
         case 3:
             item = new QGraphicsPixmapItem;
             QCOMPARE(int(item->type()), int(QGraphicsPixmapItem::Type));
             QCOMPARE(qgraphicsitem_cast<QGraphicsPixmapItem *>(item), (QGraphicsPixmapItem *)item);
             QCOMPARE(qgraphicsitem_cast<QGraphicsRectItem *>(item), (QGraphicsRectItem *)0);
+            QCOMPARE(item->flags(), 0);
             break;
         case 4:
             item = new QGraphicsPolygonItem;
             QCOMPARE(int(item->type()), int(QGraphicsPolygonItem::Type));
             QCOMPARE(qgraphicsitem_cast<QGraphicsPolygonItem *>(item), (QGraphicsPolygonItem *)item);
             QCOMPARE(qgraphicsitem_cast<QGraphicsRectItem *>(item), (QGraphicsRectItem *)0);
+            QCOMPARE(item->flags(), 0);
             break;
         case 5:
             item = new QGraphicsRectItem;
             QCOMPARE(int(item->type()), int(QGraphicsRectItem::Type));
             QCOMPARE(qgraphicsitem_cast<QGraphicsRectItem *>(item), (QGraphicsRectItem *)item);
             QCOMPARE(qgraphicsitem_cast<QGraphicsLineItem *>(item), (QGraphicsLineItem *)0);
+            QCOMPARE(item->flags(), 0);
             break;
         case 6:
-        default:
             item = new QGraphicsTextItem;
             QCOMPARE(int(item->type()), int(QGraphicsTextItem::Type));
             QCOMPARE(qgraphicsitem_cast<QGraphicsTextItem *>(item), (QGraphicsTextItem *)item);
             QCOMPARE(qgraphicsitem_cast<QGraphicsRectItem *>(item), (QGraphicsRectItem *)0);
+            // This is the only item that uses an extended style option.
+            QCOMPARE(item->flags(), QGraphicsItem::GraphicsItemFlags(QGraphicsItem::ItemUsesExtendedStyleOption));
+            break;
+        default:
+            qFatal("You broke the logic, please fix!");
             break;
         }
 
         QCOMPARE(item->scene(), (QGraphicsScene *)0);
         QCOMPARE(item->parentItem(), (QGraphicsItem *)0);
         QVERIFY(item->children().isEmpty());
-        QCOMPARE(item->flags(), 0);
         QVERIFY(item->isVisible());
         QVERIFY(item->isEnabled());
         QVERIFY(!item->isSelected());
diff --git a/tests/auto/qgraphicsview/tst_qgraphicsview.cpp b/tests/auto/qgraphicsview/tst_qgraphicsview.cpp
index 920cba7010..8e490adee1 100644
--- a/tests/auto/qgraphicsview/tst_qgraphicsview.cpp
+++ b/tests/auto/qgraphicsview/tst_qgraphicsview.cpp
@@ -2371,7 +2371,7 @@ public:
 
     void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *viewport)
     {
-        lastLod = option->levelOfDetail;
+        lastLod = option->levelOfDetailFromTransform(painter->worldTransform());
         QGraphicsRectItem::paint(painter, option, viewport);
     }