Does something like a NPR interpolation map exist?

So, I’ve had this idea for a while but don’t really know how to look into it.

Is there such a thing as a map (similar to a normal map) for NPR that lets you define curve interpolation attributes?

e.g. you have a 32 vertex sphere that will be cell shaded, and you want it to look perfectly smooth. You set vertex colours (using the map) that tell the renderer that it should interpolate the vertices with a certain kind of curve, thereby making it perfectly round in the final render.

I wished there even was the for cubic interpolation of vertex colors. So no, not out of the box.

What you can do is to create as many vertex colors as you need to determine the all curve parameters, all the colors at the vertices belonging to the current triangle (and derivatives, and whatnot) and the triangle coordinates of the shading point. Then create the interpolation function with nodes.

Of course this is a big mess, and unrealistic to do by hand, but it might be an idea for a plugin which would create the mentioned vertex color data from a script.