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Fix QGraphicsScene::update() performance

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A previous fix has caused a performance degradation while adding a
check for avoiding adding duplicated rectangles to the update list.
This patch fixes it by using a std::set instead of a QList, avoiding
duplication while using an O(log N) operation, instead of the O(N)
used before.

Fixes: QTBUG-77952
Change-Id: Ifa9fbf110e0bad60ee02a42d91281981fd98ceab
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
This commit is contained in:
Andre de la Rocha 2019-09-02 16:46:07 +02:00
parent 014d7ac654
commit 31012df705
3 changed files with 26 additions and 6 deletions
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13
src/widgets/graphicsview/qgraphicsscene.cpp
View File

@ -386,7 +386,15 @@ void QGraphicsScenePrivate::_q_emitUpdated()
// Notify the changes to anybody interested. // Notify the changes to anybody interested.
QList<QRectF> oldUpdatedRects; QList<QRectF> oldUpdatedRects;
oldUpdatedRects = updateAll ? (QList<QRectF>() << q->sceneRect()) : updatedRects; if (updateAll) {
oldUpdatedRects << q->sceneRect();
} else {
// Switch to a ranged constructor in Qt 6...
oldUpdatedRects.reserve(int(updatedRects.size()));
std::copy(updatedRects.cbegin(), updatedRects.cend(),
std::back_inserter(oldUpdatedRects));
}
updateAll = false; updateAll = false;
updatedRects.clear(); updatedRects.clear();
emit q->changed(oldUpdatedRects); emit q->changed(oldUpdatedRects);
@ -3219,8 +3227,7 @@ void QGraphicsScene::update(const QRectF &rect)
view->d_func()->updateRectF(rect); view->d_func()->updateRectF(rect);
} }
} else { } else {
if (!d->updatedRects.contains(rect)) d->updatedRects.insert(rect);
d->updatedRects << rect;
} }
} }

17
src/widgets/graphicsview/qgraphicsscene_p.h
View File

@ -69,6 +69,9 @@
#include <QtWidgets/qstyle.h> #include <QtWidgets/qstyle.h>
#include <QtWidgets/qstyleoption.h> #include <QtWidgets/qstyleoption.h>
#include <set>
#include <tuple>
QT_REQUIRE_CONFIG(graphicsview); QT_REQUIRE_CONFIG(graphicsview);
QT_BEGIN_NAMESPACE QT_BEGIN_NAMESPACE
@ -122,7 +125,19 @@ public:
QRectF growingItemsBoundingRect; QRectF growingItemsBoundingRect;
void _q_emitUpdated(); void _q_emitUpdated();
QList<QRectF> updatedRects;
struct UpdatedRectsCmp
{
bool operator() (const QRectF &a, const QRectF &b) const noexcept
{
return std::make_tuple(a.y(), a.x(), a.height(), a.width())
< std::make_tuple(b.y(), b.x(), b.height(), b.width());
}
};
// std::set was used here instead of std::unordered_set due to requiring only a comparator and
// showing equivalent performance in empirical measurements within the ranges of interest...
std::set<QRectF, UpdatedRectsCmp> updatedRects;
QPainterPath selectionArea; QPainterPath selectionArea;
int selectionChanging; int selectionChanging;

2
tests/auto/widgets/graphicsview/qgraphicsscene/tst_qgraphicsscene.cpp
View File

@ -3685,8 +3685,6 @@ void tst_QGraphicsScene::changedSignal()
qApp->processEvents(); qApp->processEvents();
QCOMPARE(cl.changes.size(), 2); QCOMPARE(cl.changes.size(), 2);
QCOMPARE(cl.changes.at(1).size(), 2); QCOMPARE(cl.changes.at(1).size(), 2);
QCOMPARE(cl.changes.at(1).first(), QRectF(0, 0, 10, 10));
QCOMPARE(cl.changes.at(1).last(), QRectF(20, 0, 10, 10));
QCOMPARE(scene.sceneRect(), QRectF(0, 0, 30, 10)); QCOMPARE(scene.sceneRect(), QRectF(0, 0, 30, 10));