Widget that allows editing of a curve.
The GtkCurve is a widget that allows the user to
directly edit a curve covering a range of values.
The GtkCurve widget has 3 modes of operation;
spline, linear and free. In spline mode the user places points on the
curve which are automatically connected together into a smooth curve.
In linear mode the user places points on the curve which are connected by
straight lines. In free mode the user can draw the points of the curve
freely, and they are not connected at all.
This widget is considered too specialized/little-used for GTK+,
and will in the future be moved to some other package. If your application needs this widget,
feel free to use it, as the widget does work and is useful in some applications; it's just
not of general interest.
Emitted when the curve type has been changed.