// adornerLayerに対する相対位置
public void UpdateCursorPosition(Point p)
{
var srcPoint = DragFrom.TranslatePoint(new Point(DragFrom.ActualWidth / 2, DragFrom.ActualHeight / 2), AdornedElement);
Line.X1 = srcPoint.X;
Line.Y1 = srcPoint.Y;
Line.X2 = p.X;
Line.Y2 = p.Y;
AdornerLayer layer = AdornerLayer.GetAdornerLayer(AdornedElement);
layer.Update(AdornedElement);
//System.Diagnostics.Debug.WriteLine("{0} UpdateCursorPosition ({1},{2}) => ({3},{4})",
// DateTime.Now.ToString("HH:mm:ss.fff"),
// srcPoint.X,
// srcPoint.Y,
// p.X,
// p.Y
// );
}
