Surface Space Curves

The proposal is to have curves that exist in the local coordinates of a surface, without having an existence in the surrounding 3D space.

In the placement of hair (with old hair system), I have currently put up with the use of meshes where I use the shrink wrap modifier to project them to the main surface to do eyelashes and eyebrows. This proposal would streamline such process by automatically moving the curves if the mesh vertices are moved. I could also switch to the new hair system (mirror modifier issues have been in the way of me switching), but this idea has further applications.

b/Surf: Interactive Bézier Splines on Surfaces 2021 by Claudio Mancinelli and Giacomo Nazzaro ( pellacini.di.uniroma1.it/publications/bsurf22/bsurf22.html ) worked on a similar idea to what I have had, but they brought it to fruition. My original idea did not pay attention to surface curvature.

The intended use cases include

• placement of spikes and teeth on a model.

• In hair, eyelashes and eyebrows, avoiding the use of a raster density texture

• Non-destructive placement of wrinkles, scales and similar features in sculpting

A further idea I have had is to have a surface space curve used as a guide to place smaller surface space curves procedurally, such as for wrinkles

Another desirable feature would be to allow the curves to branch off from an incoming curve.