The latest version of Functy in the repository now has a (roughly) working version of the curve rendering code. This allows a cylindrical coordinate cross section to be extruded along the length of a parametrically defined curve. In other words, something like a tube.
The code is fairly incomplete. Trying to define functional colours will cause a crash, and vertices are all positioned on the CPU, so that animation isn’t particularly efficient. Both of these should be fixed soon, including GPU rendering of the entire curve.
Here’s a brief video demo of this early code to give a flavour of how it can be used.