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>

1 files changed, 18 insertions, 0 deletions

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