OpenScad Revolids version 0.5

There are lots of interesting cubic curves in the world. They're interesting because with just 4 points, you can describe very interesting shapes. These curves make for nice revolutionary solids, but with OpenScad, it's kind of a challenge.

This thing generalizes the surface of revolution based on a cubic curve.

How simple is it?

The following will generate that bell shaped picture based on a Catmull-Rom cubic curve.

surface_rotationx_cubic(anglesteps = 36, stacksteps = 12,
umult = 0.5, A = cubic_catmullrom_M(),
cps = [[0, 1, 0],[2,3,0], [4,1,0],[5,2,0]]);

And this one will do the same for a standard Bezier curve based on the same control points

surface_rotationx_cubic(anglesteps = 24, stacksteps = 12,
umult = 1, A = cubic_bezier_M(),
cps = [[0, 1, 0],[2,3,0], [4,1,0],[5,2,0]]);

And the same can be done for a Hermite, or any other 'cubic' curve you can think of. The two key components are the blending function 'A', which is a 4x4 matrix, and the contro