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, 63 insertions, 4 deletions

diff --git a/src/gui/graphicsview/qgraphicsitem.cpp b/src/gui/graphicsview/qgraphicsitem.cpp
index aa55908..ec08aaf 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;