QAbstractItemView::dataChanged(): optimize call to QWidget::update()

When topLeft and bottomRight are different in QAIV::dataChanged(), the
current implementation simply calls QWidget::update() without checking
if the affected cells are visible. This results in a big performance hit
when cells are updated frequently.
Now try to compute the exact update rect by iterating through the
modified indexes.

Fixes: QTBUG-58580
Change-Id: I97de567d494e40ed8cdb1ea1f5b3cf3a2f60455e
Reviewed-by: Samuel Gaist <samuel.gaist@idiap.ch>

6 files changed, 93 insertions, 2 deletions

diff --git a/src/widgets/itemviews/qabstractitemview.cpp b/src/widgets/itemviews/qabstractitemview.cpp
index ebef36d033..b8c30321ff 100644
--- a/src/widgets/itemviews/qabstractitemview.cpp
+++ b/src/widgets/itemviews/qabstractitemview.cpp
@@ -3335,8 +3335,19 @@ void QAbstractItemView::dataChanged(const QModelIndex &topLeft, const QModelInde
         }
     } else {
         d->updateEditorData(topLeft, bottomRight);
-        if (isVisible() && !d->delayedPendingLayout)
-            d->viewport->update();
+        if (isVisible() && !d->delayedPendingLayout) {
+            if (!topLeft.isValid() ||
+                topLeft.parent() != bottomRight.parent() ||
+                topLeft.row() > bottomRight.row() ||
+                topLeft.column() > bottomRight.column()) {
+                // invalid parameter - call update() to redraw all
+                d->viewport->update();
+            } else {
+                const QRect updateRect = d->intersectedRect(d->viewport->rect(), topLeft, bottomRight);
+                if (!updateRect.isEmpty())
+                    d->viewport->update(updateRect);
+            }
+        }
     }
 
 #ifndef QT_NO_ACCESSIBILITY
@@ -3620,6 +3631,19 @@ void QAbstractItemViewPrivate::_q_columnsMoved(const QModelIndex &, int, int, co
   _q_layoutChanged();
 }
 
+QRect QAbstractItemViewPrivate::intersectedRect(const QRect rect, const QModelIndex &topLeft, const QModelIndex &bottomRight) const
+{
+    Q_Q(const QAbstractItemView);
+
+    const auto parentIdx = topLeft.parent();
+    QRect updateRect;
+    for (int r = topLeft.row(); r <= bottomRight.row(); ++r) {
+        for (int c = topLeft.column(); c <= bottomRight.column(); ++c)
+            updateRect |= q->visualRect(model->index(r, c, parentIdx));
+    }
+    return rect.intersected(updateRect);
+}
+
 /*!
     This slot is called when the selection is changed. The previous
     selection (which may be empty), is specified by \a deselected, and the
diff --git a/src/widgets/itemviews/qabstractitemview_p.h b/src/widgets/itemviews/qabstractitemview_p.h
index fe1c00248f..4b29b68b66 100644
--- a/src/widgets/itemviews/qabstractitemview_p.h
+++ b/src/widgets/itemviews/qabstractitemview_p.h
@@ -108,6 +108,7 @@ public:
     virtual void _q_layoutChanged();
     virtual void _q_rowsMoved(const QModelIndex &source, int sourceStart, int sourceEnd, const QModelIndex &destination, int destinationStart);
     virtual void _q_columnsMoved(const QModelIndex &source, int sourceStart, int sourceEnd, const QModelIndex &destination, int destinationStart);
+    virtual QRect intersectedRect(const QRect rect, const QModelIndex &topLeft, const QModelIndex &bottomRight) const;
 
     void _q_headerDataChanged() { doDelayedItemsLayout(); }
     void _q_scrollerStateChanged();
diff --git a/src/widgets/itemviews/qtableview.cpp b/src/widgets/itemviews/qtableview.cpp
index 81fceba8dc..c3ccfac5be 100644
--- a/src/widgets/itemviews/qtableview.cpp
+++ b/src/widgets/itemviews/qtableview.cpp
@@ -669,6 +669,52 @@ void QTableViewPrivate::trimHiddenSelections(QItemSelectionRange *range) const
     *range = QItemSelectionRange(topLeft, bottomRight);
 }
 
+QRect QTableViewPrivate::intersectedRect(const QRect rect, const QModelIndex &topLeft, const QModelIndex &bottomRight) const
+{
+    Q_Q(const QTableView);
+
+    using minMaxPair = std::pair<int, int>;
+    const auto calcMinMax = [q, rect](QHeaderView *hdr, int startIdx, int endIdx, minMaxPair bounds) -> minMaxPair
+    {
+        minMaxPair ret(std::numeric_limits<int>::max(), std::numeric_limits<int>::min());
+        if (hdr->sectionsMoved()) {
+            for (int i = startIdx; i <= endIdx; ++i) {
+                const int start = hdr->sectionViewportPosition(i);
+                const int end = start + hdr->sectionSize(i);
+                ret.first = std::min(start, ret.first);
+                ret.second = std::max(end, ret.second);
+                if (ret.first <= bounds.first && ret.second >= bounds.second)
+                    break;
+            }
+        } else {
+            if (q->isRightToLeft() && q->horizontalHeader() == hdr)
+                std::swap(startIdx, endIdx);
+            ret.first = hdr->sectionViewportPosition(startIdx);
+            ret.second = hdr->sectionViewportPosition(endIdx) +
+                         hdr->sectionSize(endIdx);
+        }
+        return ret;
+    };
+
+    const auto yVals = calcMinMax(verticalHeader, topLeft.row(), bottomRight.row(),
+                                  minMaxPair(rect.top(), rect.bottom()));
+    if (yVals.first == yVals.second) // all affected rows are hidden
+        return QRect();
+
+    // short circuit: check if no row is inside rect
+    const QRect colRect(QPoint(rect.left(), yVals.first),
+                        QPoint(rect.right(), yVals.second));
+    const QRect intersected = rect.intersected(colRect);
+    if (intersected.isNull())
+        return QRect();
+
+    const auto xVals = calcMinMax(horizontalHeader, topLeft.column(), bottomRight.column(),
+                                  minMaxPair(rect.left(), rect.right()));
+    const QRect updateRect(QPoint(xVals.first, yVals.first),
+                           QPoint(xVals.second, yVals.second));
+    return rect.intersected(updateRect);
+}
+
 /*!
   \internal
   Sets the span for the cell at (\a row, \a column).
diff --git a/src/widgets/itemviews/qtableview_p.h b/src/widgets/itemviews/qtableview_p.h
index 8f174351d2..e17773c4bd 100644
--- a/src/widgets/itemviews/qtableview_p.h
+++ b/src/widgets/itemviews/qtableview_p.h
@@ -149,6 +149,7 @@ public:
  }
     void init();
     void trimHiddenSelections(QItemSelectionRange *range) const;
+    QRect intersectedRect(const QRect rect, const QModelIndex &topLeft, const QModelIndex &bottomRight) const override;
 
     inline bool isHidden(int row, int col) const {
         return verticalHeader->isSectionHidden(row)
diff --git a/src/widgets/itemviews/qtreeview.cpp b/src/widgets/itemviews/qtreeview.cpp
index 9aba17be70..a3bebb8f3c 100644
--- a/src/widgets/itemviews/qtreeview.cpp
+++ b/src/widgets/itemviews/qtreeview.cpp
@@ -1396,6 +1396,24 @@ void QTreeViewPrivate::_q_modelDestroyed()
     QAbstractItemViewPrivate::_q_modelDestroyed();
 }
 
+QRect QTreeViewPrivate::intersectedRect(const QRect rect, const QModelIndex &topLeft, const QModelIndex &bottomRight) const
+{
+    Q_Q(const QTreeView);
+
+    const auto parentIdx = topLeft.parent();
+    executePostedLayout();
+    QRect updateRect;
+    for (int r = topLeft.row(); r <= bottomRight.row(); ++r) {
+        if (isRowHidden(model->index(r, 0, parentIdx)))
+            continue;
+        for (int c = topLeft.column(); c <= bottomRight.column(); ++c) {
+            const QModelIndex idx(model->index(r, c, parentIdx));
+            updateRect |= q->visualRect(idx);
+        }
+    }
+    return rect.intersected(updateRect);
+}
+
 /*!
   \reimp
 
diff --git a/src/widgets/itemviews/qtreeview_p.h b/src/widgets/itemviews/qtreeview_p.h
index 836d8f0c2d..1206850b71 100644
--- a/src/widgets/itemviews/qtreeview_p.h
+++ b/src/widgets/itemviews/qtreeview_p.h
@@ -135,6 +135,7 @@ public:
     void _q_modelAboutToBeReset();
     void _q_sortIndicatorChanged(int column, Qt::SortOrder order);
     void _q_modelDestroyed() override;
+    QRect intersectedRect(const QRect rect, const QModelIndex &topLeft, const QModelIndex &bottomRight) const override;
 
     void layout(int item, bool recusiveExpanding = false, bool afterIsUninitialized = false);