Family grapples with bipolar father’s illness in ‘Infinitely Polar Bear’

Starring Mark Ruffalo, Zoe Saldana and Imogene Wolodarsky. Directed by Maya Forbes.

Rated R for language. Check listings for theaters. 1 hour, 30 minutes.

Bottom line: Worth seeing though could've looked more at challenges

How much funny goes with the crazy? Facile as it sounds, this is the question guiding the efforts of a considerable number of writer-directors over the years, as they have brought family stories (often autobiographical) involving some form of mental illness to the screen.

The latest of these is “Infinitely Polar Bear,” writer-director Maya Forbes’ agreeable but dodgy film based on Forbes’ experiences growing up with a bipolar father in 1970s-era Cambridge, Mass. It’s worth seeing, on balance, simply for what Mark Ruffalo does in a hundred different, discrete, telling ways as he creates a character who was a capital-A Character, outlandish one minute, scarily unpredictable the next.

Forbes’ writing credits include “The Larry Sanders Show” and an undervalued little Rainn Wilson vehicle from 2008, “The Rocker.” She also worked on “Monsters vs. Aliens” and a “Wimpy Kid” movie. Similarly warring dictates of sincerity and punch lines set the zigzagging course of “Infinitely Polar Bear.”

We meet Cam, the Ruffalo character, as he pedals desperately on a bike wearing only red underwear, pleading with his wife Maggie (Zoe Saldana) and their daughters (Imogene Wolodarsky and Ashley Aufderheide) to take him back. The movie is all about second chances. The year is 1978. Cam’s most severe manic episode lands him in a hospital; Maggie and the girls leave their house in the country for a small apartment in Cambridge.

Can he take care of them? While Maggie pursues a business degree at Columbia University in New York, Cam, now out of the hospital and trying to stick with his Lithium, is charged with the responsibilities of primary caregiving. Forbes’ film charts a year in these lives, a father and two wary daughters in the orbit of a guardian who is “totally polar bear,” in the phrase of one of the girls.

Ruffalo isn’t the whole show; though it’s frustrating she never emerges as three-dimensional as written, Saldana is smooth and accomplished throughout. But Ruffalo remains the most truthful aspect of a show that never quite settles that crucial question of seriocomic tone. Smoking one cigarette while holding another, darting through his impulses on the way to grander or lesser ones, his Cam comports himself like a Beacon Hill dandy who can’t quite figure out how he came to his present, chaotic circumstances. It’s a zesty performance, as well as a pleasurable change of pace from the easygoing rhythms and mellow demands of so many other Ruffalo portrayals.

Forbes clearly adored her father, for all his complications and challenges. I wish her movie wrestled with the mess more fully. Theodore Shapiro’s reassuring musical score is all too suited to the peppy personality of the movie itself, which is full of shrewd grace notes that leave you somewhat less than full.