Skin-deep knee-scratcher about “global b-boying,” once known as breakdancing, “Planet B-Boy” is a niche documentary for a specific audience, who may find the familiar narrative structure and content reassuring. Building to a 2005 “Battle of the Year” with competitors from eighteen countries, director Benson Lee does one good thing: he respects the energy of his performers through framing them properly, rather than in chewed-up little bits like too much music-related nonfiction product. A German promoter is featured, as well as four crews from the U.S., Japan, France and South Korea, seen moving toward the competition. The invocation of “Flashdance” as a lodestar of inspiration is gratifying. 98m. (Ray Pride)