This program allows drawing of 3D free form explicit
algebraic surfaces of the form: x = X(u,v), y = Y(u,v), z = Z(u,v),
where u,v are the parametric domain parameters.The program displays
the surface by sampling it along its isoparametriccurves, and
approximating (with settable accuracy) them as piecewise linear
polylines. It it also possible to save the surface as a collection
of polygons approximating the surface (again with settable accuracy).
As on line help is available which can be modifies.
(from the documentation)
drawfn3s.zip contains the C source code for this program.