Proper library detection on different systems
Right now the SDL library is hardcoded in the lib/doomfire/ffi_sdl.rb file and what's worse, it's hardcoded to a .dylib file, which is exclusive to macOS.
It works fine for me, since I have a macbook, but I don't have a Linux or Windows machine to test how it should be working on different systems.
How about using rubysdl gem, that way it's handled?
I'm not really convinced that depending on a whole library is the right way when the point is to just use an extremely small subset of its functions.
Especially if we're talking about a library which seems to include its own C extension (and to SDL 1.2) as opposed to being a set of FFI/Fiddle bindings to whatever the user has installed on their system.
Additionally, changing it to this library would require considerably much more effort than just introducing library detection.