I added a new class skeleton called SkyDrawer. It will be the one taking care of drawing point sources or disk sources and taking care of all the tricky FOV/Eye adaptation/color dependencies.
My idea is that an instance of it will be part of StelCore, and it will be used by StarMgr, SolarSystem, and any other module which needs to render sky point sources or disk halos. This class will definitely simplify the code by having a centralized point for doing this central operation.

Part of the code of the stars drawing should move into it (the MagConverter class).
The problem now is to try to make something as fast as it is done in StarMgr, but with more generical interfaces, i.e. pre-computation of color and brightness by b-v/magnitude steps should ideally be hidden into it. I think it is feasible but the interfaces for drawPointSource/drawDiskSource might need to be changed a bit though (maybe it would be better to use an index instead of floating values for b-v and mag).

What do you think?