ItemViews: make dragging faster when lots of items are selected

QListView know exactly what they have on their viewport and we only
paint items clipped to the viewport. So we don't need to ask for each
item its visualRect.
NB: QTreeView and QTableView probably deservee the same treatment

1 files changed, 26 insertions, 0 deletions

diff --git a/src/gui/itemviews/qlistview.cpp b/src/gui/itemviews/qlistview.cpp
index 6ff516a..44bcf6f 100644
--- a/src/gui/itemviews/qlistview.cpp
+++ b/src/gui/itemviews/qlistview.cpp
@@ -709,6 +709,32 @@ void QListViewPrivate::selectAll(QItemSelectionModel::SelectionFlags command)
         selectionModel->select(selection, command);
 }
 
+/*!
+  \reimp
+
+  We have a QListView way of knowing what elements are on the viewport
+  through the intersectingSet function
+*/
+QItemViewPaintPairs QListViewPrivate::draggablePaintPairs(const QModelIndexList &indexes, QRect *r) const
+{
+    Q_ASSERT(r);
+    Q_Q(const QListView);
+    QRect &rect = *r;
+    const QRect viewportRect = viewport->rect();
+    QItemViewPaintPairs ret;
+    intersectingSet(viewportRect);
+    const QSet<QModelIndex> visibleIndexes = intersectVector.toList().toSet();
+    for (int i = 0; i < indexes.count(); ++i) {
+        const QModelIndex &index = indexes.at(i);
+        if (visibleIndexes.contains(index)) {
+            const QRect current = q->visualRect(index);
+            ret += qMakePair(current, index);
+            rect |= current;
+        }
+    }
+    rect &= viewportRect;
+    return ret;
+}
 
 /*!
   \internal