private void BuildAdornerCorners(ref Thumb cornerThumb, Cursor customizedCursors)
{
//adding new thumbs for adorner to visual childern collection
if (cornerThumb != null)
{
return;
}
cornerThumb = new Thumb();
cornerThumb.Style = cornerThumb.FindResource("RoundThumbStyle") as Style;
mVisualChildren.Add(cornerThumb);
}