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

1 files changed, 2 insertions, 32 deletions

diff --git a/src/gui/graphicsview/qgraphicsscene.cpp b/src/gui/graphicsview/qgraphicsscene.cpp
index c421f05..7318fa5 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);