private static void MoveBottomEdgeOfWindowToMousePosition(PopupWindow window, double width)
{
var transform = PresentationSource.FromVisual(window).CompositionTarget.TransformFromDevice;
var mouse = transform.Transform(new Point(PT.X, PT.Y));
window.Left = mouse.X - width - 15;
window.Top = mouse.Y - 20;
window.InvalidateVisual();
}