Прочесть можеш в разделе: SplineShape : Shape
У каждой точки в безье кривой есть два параметра - invec , outvec
Если ты только строиш прямую то можеш укарать сразу все параметры
addKnot <shape> <spline_index_integer> \
( #smooth | #corner | #bezier | #bezierCorner ) \
( #curve | #line ) <position_point3> \
[invec_point3 outvec_point3] \
[where_integer]
Если нужно управлять у готовой :
getKnotType <shape> <spline_index_integer> <knot_index_integer>
Returns the knot type of the indexed knot in the indexed spline. The value is one of the names #smooth, #corner, #bezier, or #bezierCorner.
setKnotType <shape> \
<spline_index_integer> \
<knot_index_integer> \
(#smooth | #corner | #bezier | #bezierCorner )
getInVec <shape> <spline_index_integer> <knot_index_integer>
Retrieves the coordinates of the in-vector handle for the indexed knot as a point3 in the current working coordinate system.
setInVec <shape> <spline_index_integer> <knot_index_integer> <point3>
Sets the coordinates of the in-vector handle of the indexed knot. Coordinates are given in the current working coordinate system.
getOutVec <shape> <spline_index_integer> <knot_index_integer>
Retrieves the coordinates of the out-vector handle for the indexed knot as a point3 in the current working coordinate system.
setOutVec <shape> <spline_index_integer> <knot_index_integer> <point3>
Sets the coordinates of the out-vector handle of the indexed knot. Coordinates are given in the current working coordinate system.
незабудь в коце проапдейтить - updateShape()