The animation company that changed the face of big-screen cartoons is celebrating it’s 20th anniversary. Pixar, which counts Finding Nemo and Monsters, Inc. among its hit films, dragged Hollywood into the age of digital animation more or less single-handedly, thus setting off a raging debate on whether computer-generated characters can ever really have the humanity of a hand-drawn version. Pixar’s chief stands firm: “Computers don’t create computer animation any more than a pencil creates pencil animation. What creates computer animation is the artist.”