public virtual void MouseButtonUp (MouseButtonEventArgs args)
{
if (args.Button != MouseButton.PrimaryButton &&
args.Button != MouseButton.WheelUp &&
args.Button != MouseButton.WheelDown)
return;
if (mouseDownElement != null) {
if (args.Button == MouseButton.PrimaryButton)
mouseDownElement.MouseButtonUp (args);
mouseDownElement = null;
}
}