void PlotWidget_ButtonPressEvent(object o, ButtonPressEventArgs args)
{
int X, Y;
Gdk.ModifierType state;
args.Event.Window.GetPointer(out X, out Y, out state);
// state = args.Event.State;
// X = (int)args.Event.X;
// Y = (int)args.Event.Y;
Modifier keys = MouseInput(state);
this.InteractivePlotSurface2D.DoMouseDown(X, Y, keys);
}