private void HandleMotionNotifyEvent(object o, Gtk.MotionNotifyEventArgs args)
{
int px, py;
Gdk.ModifierType mask;
GdkWindow.GetPointer (out px, out py, out mask);
int index = FindValueIndex (py);
py = (int)NormalizeY (index, py);
if (mask == Gdk.ModifierType.Button1Mask) {
if (index != -1) {
double y = GetValueFromY (py);
vals[index] = y;
OnValueChanged (index);
}
}
//to avoid unnessesary costly redrawing
if (index != -1)
GdkWindow.Invalidate ();
}