Windows QPA: Fix slowdown with large table/tree views with accessibility

The accessibility code for notifying focus changes related to a
table/tree view was iterating over all items to find the focused one,
which for a very large number of items could cause a major slowdown
and UI freeze. This patch avoids the issue by removing the loop and
implementing the focusChild() method in the table/tree accessibility
classes.

Fixes: QTBUG-100997
Pick-to: 6.2 6.3 5.15
Change-Id: I04c847a5e65223b7a93ab82363feb32e1ebab9f3
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

2 files changed, 25 insertions, 0 deletions

diff --git a/src/widgets/accessible/itemviews.cpp b/src/widgets/accessible/itemviews.cpp
index a7b536ae54..e485744dc8 100644
--- a/src/widgets/accessible/itemviews.cpp
+++ b/src/widgets/accessible/itemviews.cpp
@@ -425,6 +425,15 @@ QAccessibleInterface *QAccessibleTable::childAt(int x, int y) const
     return nullptr;
 }
 
+QAccessibleInterface *QAccessibleTable::focusChild() const
+{
+    QModelIndex index = view()->currentIndex();
+    if (!index.isValid())
+        return nullptr;
+
+    return child(logicalIndex(index));
+}
+
 int QAccessibleTable::childCount() const
 {
     if (!view()->model())
@@ -692,6 +701,20 @@ QAccessibleInterface *QAccessibleTree::childAt(int x, int y) const
     return child(i);
 }
 
+QAccessibleInterface *QAccessibleTree::focusChild() const
+{
+    QModelIndex index = view()->currentIndex();
+    if (!index.isValid())
+        return nullptr;
+
+    const QTreeView *treeView = qobject_cast<const QTreeView*>(view());
+    int row = treeView->d_func()->viewIndex(index) + (horizontalHeader() ? 1 : 0);
+    int column = index.column();
+
+    int i = row * view()->model()->columnCount() + column;
+    return child(i);
+}
+
 int QAccessibleTree::childCount() const
 {
     const QTreeView *treeView = qobject_cast<const QTreeView*>(view());
diff --git a/src/widgets/accessible/itemviews_p.h b/src/widgets/accessible/itemviews_p.h
index 683ae9c948..1fc6a3e521 100644
--- a/src/widgets/accessible/itemviews_p.h
+++ b/src/widgets/accessible/itemviews_p.h
@@ -79,6 +79,7 @@ public:
     QRect rect() const override;
 
     QAccessibleInterface *childAt(int x, int y) const override;
+    QAccessibleInterface *focusChild() const override;
     int childCount() const override;
     int indexOfChild(const QAccessibleInterface *) const override;
 
@@ -154,6 +155,7 @@ public:
 
 
     QAccessibleInterface *childAt(int x, int y) const override;
+    QAccessibleInterface *focusChild() const override;
     int childCount() const override;
     QAccessibleInterface *child(int index) const override;