Files are written to the libretro save directory, which is mounted at
/save in PhysFS. All filesystem calls made from Ruby in libretro builds
are routed through PhysFS, so the game can just use any ordinary
filesystem function provided by Ruby to interact with /save.
It's also union mounted on top of the game directory (located at /game
in PhysFS) so that games that write their save files to the current
working directory will have their save files saved to the libretro save
directory instead of the game directory.
For security and portability reasons, nothing outside of the libretro
save directory can be written to, and nothing outside of the libretro
save directory, the libretro game directory and the various embedded
files used by the runtime can be read from.
I don't think I'll be needing SDL. Pretty sure about 100% of the
functionality of SDL that's currently being used here is either trivial
to reimplement or needs to be replaced for the libretro core to work in
the first place. For example, I already know I'm going to need to
completely replace the SDL input handling with libretro's input API.
Also, I'll need to get rid of the use of SDL threads in the audio code
later because libretro cores need to render audio synchronously with the
video rendering.
I'm including the SDL headers, though, to reduce the number of
compilation errors.
