It’s not just that an interview with a rock star while he is in the dentist’s chair having his teeth drilled is far from the weirdest thing in this movie. It’s more that the whole story is so weird that by the time you get to the interview, it seems like the most natural thing in the world.

Daniel Johnston lives in that fragile no man’s land between genius and sanity. His mental illness keeps him viscerally in touch with primal adolescent anguish. And of course primal adolescent anguish is the best possible fuel for rock songs — and the people who listen to them. The songs are undiluted emotion, as focused as a laser beam, emotion so all-encompassing that its simplicity is heartbreaking.

Look at his self-produced album titles: “Songs of Pain,” “More Songs of Pain,” “Rejected Unknown,” “Why Me.” The album covers are his simple line drawings of comic book characters and weird creatures. They look like doodles made in study hall. The Whitney Biennial, the most prestigious forum in the United States for new artists, features an entire wall of Johnston’s drawings.

Johnston was prodigious and prolific from beginning, obsesively documenting himself even as a young teenager. The hundreds of hours of archival tapes and footage are the heart of this film, surrounded by interviews with friends, fans, and family.

Johnston alternated between mental hospitals and performances. He had a small but vibrant cult following. It included influential rock stars like Kurt Cobain, who wore a t-shirt featuring one of Johnston’s album cover drawings often during the last year of his life. His songs were covered by Cobain, Sonic Youth, and Yo La Tengo. And he still lives with his parents, who are getting old and very tired.

Director Jeff Feuerzeig is sympathetic but clear-eyed. He understands that Johnston has a tortured soul, but he understands that he has also inflicted great pain on those around him. He abruptly fired Jeff Tartakov, the manager who was utterly devoted to him. His father was piloting a small plane when, in the midst of some massive delusion, he reached over and yanked the keys out of the ignition and threw them out of the window. The plane crashed into the treetops. It was shattered but Johnston and his parents survived.

Feuerzeig has a fractionated, mosaic approach that suits the high-strung nature of his story. Johnston’s music and artwork are a matter of taste, but his story is compelling and sensitively explored. It is hearbreaking to see the once-so-hopeful and promising teenager become a lumbering, uncertain, unhappy man who does not seem to feel connected to anyone else. But it is inspiring to see those who feel so connected to him and to become connected ourselves.

Parents should know that the themes of this film may be very disturbing for some viewers. There are tense and sad moments and references to drug use, and characters use some strong language.

Families who see this film should talk about the choices made by Johnston’s parents and what their views are about the best way to care for family members who cannot take care of themselves. Would Johnston be as interesting and as successful if he was less disturbed?

Families who enjoy this film will also enjoy Tarnation. And they will enjoy this interview with the director. They might like to listen to Discovered/Covered, with both Daniel Johnston’s original recordings and covers by Beck, Tom Waits, Vic Chesnutt, Bright Eyes, Calvin Johnson, and others. They might also like to learn more about visionary art made by those, like Johnston, with no formal training.