‘Infinitely Polar Bear’: Mark Ruffalo moving as a dad doomed to be imperfect

We veer close to the edge of Precious, Indie-Hipster Cliche so often in “Infinitely Polar Bear,” but thanks to a gifted filmmaker and two brilliant lead performances, the voice-over narration and the home-movie footage and the flights of fancy aren’t as off-putting as they might have been in lesser hands.

“Infinitely Polar Bear” is told mostly from the point of view of Amelia (Imogene Wolodarsky), the oldest daughter of Maggie (Zoe Saldana) and Cam (Mark Ruffalo). Amelia tells us her father was diagnosed as manic-depressive in 1967, when he was found wandering Cambridge wearing a fake beard and saying his name was Jesus John Harvard.

We pick up the story in 1978, on a bright and lovely morning when Cam tells Amelia and her younger sister Faith (Ashley Aufderheide) they don’t have to go to school because Daddy just got fired again, and isn’t that wonderful, and they’re going to go mushroom-picking and make an omelet for Mommy.

Uh-oh.

Cam veers from those moments of frantic, frighteningly upbeat, whirling-dervish activities to alarm-bell-ringing bursts of temper, as when he rips out pieces of the engine on the family’s old beater of a car so Maggie won’t be able to leave with the kids.

Ruffalo does a magnificent job of conveying Cam’s charm and undeniable love for his wife and children — as well as the devastating effects of serious, incurable mental illness. His mood swings can be tempered with treatment and medication, but Cam is never going to be anything less than unpredictable, even on his best days.

Cam comes from an old-money Boston family, but his grandmother keeps a tight grip on the purse strings. (When he visits her and asks for money to send the girls to private school, she says that would send the wrong message to the children.) He’s unable to hold down a job, so it’s Maggie who takes any work she can find, and Maggie who applies for and gets a scholarship to pursue an MBA in New York City.

This leaves Cam in charge of the children, who adore their father but are often horrified by his embarrassing behavior. (Often their roles are reversed, with Amelia and Faith telling Cam to clean up his act and to stop acting so weird with the neighbors and to let them have their own friends and their own lives.)

Even though “Infinitely Polar Bear” is set mostly in the Boston of the late 1970s and Cam and Maggie are a biracial couple, there’s very little mention of race, save for a moment where Maggie lays out the difference between white people being poor and black people being poor — and a scene in which Amelia tells her father she doesn’t look black at all, and Cam says her mother is black so of course she’s black, and Amelia says fine, she’ll keep telling people she’s black even though they look at her like she’s delusional. (Given the Rachel Dolezal story, that scene got a huge laugh at the preview screening.)

Writer/director Maya Forbes based “Infinitely Polar Bear” partly on her childhood as the daughter of a white, Boston Brahmin, bipolar father and an African-American mother who put herself through business school and was the family breadwinner at a time when that was highly unusual.

Saldana gives one of her best performances as Maggie, who is torn apart by the prospect of leaving her children largely in the care of Cam for 18 months because she sees no other way. Ruffalo throws himself into the role of Cam, chain-smoking, wearing ridiculous outfits, exploding in fits of rage and yet filled with tender love for his two girls. A simple scene in which Cam wants to take the girls on the lake after school but they’d rather spend time with their friends is perfect and heartbreaking in the way it plays out.

[s3r star=3/4]

Sony Pictures Classics presents a film written and directed by Maya Forbes. Running time: 88 minutes. Rated R (for language). Opens Friday at local theaters.