I installed allegro 5 from the Debian packages, and a small example program causes the following output at exit:
Since I'm running Debian inside Virtualbox, I suppose there's a chance that this is related to bad X11 graphics drivers, but surely I can't be the first person to do this? Is there a solution?
Source below, for reference. When I remove the al_flip_display() call, no error occurs.
All I can tell you is that that code looks fine, and it works fine on my (debian-based) non-virtualised Mint 14.2. system.
At the moment I don't have a virtualbox debian image laying around to test on.
I always chalked it up to driver issues, but perhaps there really is something wrong with what Allegro does that only shows up in a virtual environment. That said, this isn't the only place where such errors happen. E.g. ex_multiwin reliably causes a quit-time X error as well on my system (even if not virtualized).
I don't actually know how to easily debug these issues, as these errors are somewhat asynchronous. We'd have to sync every X11 call I guess to really nail it down.