Pen input improvement

src/Avalonia.Controls.TreeDataGrid/Primitives/TreeDataGridRow.cs

@@ -152,9 +152,17 @@ protected override void OnPointerMoved(PointerEventArgs e)
         {
             base.OnPointerMoved(e);
 
-            var delta = e.GetPosition(this) - _mouseDownPosition;
+            var currentPoint = e.GetCurrentPoint(this);
+            var delta = currentPoint.Position - _mouseDownPosition;
 
-            if (!e.GetCurrentPoint(this).Properties.IsLeftButtonPressed || 
+            var pointerSupportsDrag = currentPoint.Pointer.Type switch
+            {
+                PointerType.Mouse => currentPoint.Properties.IsLeftButtonPressed,
+                PointerType.Pen => currentPoint.Properties.IsRightButtonPressed,
+                _ => false
+            };
+
+            if (!pointerSupportsDrag ||
                 e.Handled ||
                 Math.Abs(delta.X) < DragDistance && Math.Abs(delta.Y) < DragDistance ||
                 _mouseDownPosition == s_InvalidPoint)

src/Avalonia.Controls.TreeDataGrid/Selection/TreeDataGridCellSelectionModel.cs

@@ -140,12 +140,19 @@ void ITreeDataGridSelectionInteraction.OnPointerPressed(TreeDataGrid sender, Poi
             // Select a cell on pointer pressed if:
             //
             // - It's a mouse click, not touch: we don't want to select on touch scroll gesture start
+            // - It's a pen secondary button press, we don't want to select on primary button scroll gesture start
             // - The cell isn't already selected: we don't want to deselect an existing multiple selection
             //   if the user is trying to drag multiple cells
             //
             // Otherwise select on pointer release.
+            var pointerSupportSelectionOnPress = e.Pointer.Type switch
+            {
+                PointerType.Mouse => true,
+                PointerType.Pen => e.GetCurrentPoint(null).Properties.IsRightButtonPressed,
+                _ => false
+            };
             if (!e.Handled &&
-                e.Pointer.Type == PointerType.Mouse &&
+                pointerSupportSelectionOnPress &&
                 e.Source is Control source &&
                 sender.TryGetCell(source, out var cell) &&
                 !IsSelected(cell.ColumnIndex, cell.RowIndex))

src/Avalonia.Controls.TreeDataGrid/Selection/TreeDataGridRowSelectionModel.cs

@@ -318,12 +318,19 @@ void ITreeDataGridSelectionInteraction.OnPointerPressed(TreeDataGrid sender, Poi
             // Select a row on pointer pressed if:
             //
             // - It's a mouse click, not touch: we don't want to select on touch scroll gesture start
+            // - It's a pen secondary button press, we don't want to select on primary button scroll gesture start
             // - The row isn't already selected: we don't want to deselect an existing multiple selection
             //   if the user is trying to drag multiple rows
             //
             // Otherwise select on pointer release.
+            var pointerSupportSelectionOnPress = e.Pointer.Type switch
+            {
+                PointerType.Mouse => true,
+                PointerType.Pen => e.GetCurrentPoint(null).Properties.IsRightButtonPressed,
+                _ => false
+            };
             if (!e.Handled &&
-                e.Pointer.Type == PointerType.Mouse &&
+                pointerSupportSelectionOnPress &&
                 e.Source is Control source &&
                 sender.TryGetRow(source, out var row) &&
                 _source.Rows.RowIndexToModelIndex(row.RowIndex) is { } modelIndex &&