Hi Christian, I have recently seen that you are using the Alien::SDL 1.2 with SDL_perl 2.2.6. I am the maintiner for SDL_perl and SDL. The new module (and working) bindings for SDL in perl is called the SDL module. Please consider updating your index and installing that.
http://search.cpan.org/~froggs/SDL-2.403/ Regards, Kartik Thakore