Writing from scratch a new sdl widget would take a lot of time so I've looked for existing projects.

There are many sdl widget but most of them are in c++:

 * [[http://picogui.org/|picogui]] in c++
 * [[http://www.newimage.com/~rhk/SDL_gui/|SDL_gui]] in c++ && unmantained! :|
 * [[http://libuta.sourceforge.net/|libuta]] in c++
 * [[http://libksd.sourceforge.net/|libksd]] it's a full featured cross platform game framework but it's in c++
 * [[http://www.paragui.org/|paragui]] it's in c++
 * [[http://www.beatforce.org/|sdltk]] it's part of beatforce and in c :D
 * [[http://eboxy.sourceforge.net|eboxy]] eboxy is a small Linux application for building user interfaces for set-top boxes. Has a sdl gui in c