“I’m fascinated by giganticness,” reveals Santa-bearded mosaic artist Isaiah Zagar, whose compulsive, nearly half-century-long mission to create candy-colored mazes of fractured tiles, mirror shards, paint, and bric-a-brac has covered tens of thousands of Philadelphia’s square feet, including the home Zagar shares with wife Julia. An inwardly distressed, self-absorbed eccentric who is unafraid to expose himself, both physically and emotionally, Isaiah bluntly admits that he was molested as a boy and attempted suicide in his 20s, and, midway through the film’s production, tells Julia on camera that he’s been sleeping with his assistant. Where most documentarians would rest on the laurels of a great subject and riveting present-tense drama, director Jeremiah Zagar has observed too much of his father’s creative logic to cheat us with artless hagiography. In dreamily paced tracking shots, macro close-ups, time-lapse glimpses of Isaiah’s processes (the raking together of paint and cement is especially satisfying), archival footage, and animation, In a Dream exhibits as much beauty and sensuality as Isaiah’s work, while the unabashedly personal nature of the filmmaker/subject dynamic is as candid about familial madness as Tarnation, and captures more insight than those Friedmans did.