Walden Media is heading for the library, acquiring feature film rights to the humorous sci-fi graphic novel “Rex Libris.”The series follows Rex Libris, head librarian at the Middleton Public Library — who’s over 1,000 years old and also the librarian at the Library of Alexandria. He’s also aided by an ancient god who lives beneath the library branch and travels to the farthest reaches of the galaxy in search of overdue books and to confront alien warlords who refuse to pay their late fees. “Rex Libris,” authored by James Turner, was issued quarterly by Slave Labor Graphics between 2005, starting with “I, Librarian,” and 2008. Slave Labor Graphics will be at Comic-Con. Warner Bros. had announced in 2007 that “Rex Libris” was in development with Mosaic Media producing. Walden specializes in family-oriented titles including “The Chronicles of Narnia” series, “Journey to the Center of the Earth,” “Nim’s Island,” “Charlotte’s Web” and the doc “Waiting for ‘Superman.’” Upcoming films include “Journey 2: The Mysterious Island.” Evan Turner and Michael Bostick are handling “Rex Libris” for Walden. Brent Lilley handling for Slave Labor Graphics.