GtkCurve::set_curve_type

Use this method when you want to set the type of the curve that you want the user to draw. The existing curve will remain unchanged except when changing from a free curve to a linear or spline curve, in which case, the curve will be changed as little as possible.

Pass 0 as a parameter if you want the curve type to be linear, 1 for a spline curve and 2 for a free type curve.