PARK CITY, Utah — — Maya Forbes knew the story all too well, but she waited a long time to write a script based on her childhood.
It's understandable why the writer-director wasn't rushing. Her father was manic-depressive, and when her mother left their Cambridge, Mass., home to attend graduate school in New York, a 10-year-old Forbes and her sister were largely left in their father's care, which was far from normal — let alone safe — parenting.
Forbes, 45, who has writing credits on "The Larry Sanders Show" and the animated movie "Monsters vs. Aliens," said as a parent she has encouraged her children not to be timid. "I was always telling them, 'You have to be bold. You have to take risks. You have to put yourself out there.'"
PHOTOS: Sundance Film Festival 2014 must-see movies
But she realized that, because she couldn't commit to turning her childhood into a movie, as she had promised herself, she was failing to lead by example. So Forbes set aside her fears and started writing, and the terrors and joys of her upbringing spilled out.
Because it was so personal and she worried that another director might depict the family with too much judgment, Forbes decided to direct it herself. "I wanted it to be about love," she said.
In the resulting Sundance Film Festival feature "Infinitely Polar Bear," a mispronunciation of bipolar disorder, Forbes revisits a 1970s childhood in which her father would leave his children alone while he visited bars in the middle of the night, clutter their apartment with dozens of abandoned projects and still somehow keep everything (including himself) from falling completely apart.
The film, which lost its financing on two occasions, arrived in Park City in search of a theatrical distributor. Forbes' feature debut was helped to the screen by producer J.J. Abrams, whose company, Bad Robot, has a producing credit on the film. At Sundance, the film met with a mixed reaction, including some critics who found it too sweet and superficial.
LIST OF SUNDANCE SELECTIONS: U.S. and World Cinema dramatic competition
As played by Mark Ruffalo in the lightly fictionalized drama, Cam Stuart is a devoted father of two girls, Faith and Amelia (the latter played by Forbes' daughter, Imogene Wolodarsky).
At the film's outset, Cam is suffering from a particularly manic episode, which leaves his African-American wife, Maggie (Zoe Saldana), cowering with the young girls. A nervous breakdown lands Cam in a mental hospital, where he is drugged to the point of stupefaction.
Even if Cam and Maggie's marriage can't survive, the two are determined to keep the family more or less intact, a challenge magnified by Maggie's decision to get an MBA from Columbia University. The movie unfolds around the year and a half when Maggie is in college.
"My mother was a real role model for me, ultimately," said Forbes, whose sister, China Forbes, is the lead singer of Pink Martini. "She was really stuck, and she was not going to have it. She wanted us to go to great schools, and she just wanted a better life."
Because "Polar Bear" offers an unusually compassionate perspective on mental illness, Cam's sudden role as a single parent is not depicted as a horror story. Yes, Cam makes a series of bad decisions and struggles in the most basic parental duties, but his love for his children is as boundless as his frenzy. In that regard, it's more reminiscent of "Silver Linings Playbook" than "Shutter Island"; Maggie realizes that the father of her children is sick, but she ultimately trusts that he will do right.
PHOTOS: Sundance Film Festival 2014 | The Scene
Ruffalo plays the part with a regal bearing, walking as if he were a king in his castle. He said he was fortunate to have seen several home movies of Forbes' father, including one of his more manic episodes. "I watched those over and over and over again," Ruffalo said.
But Ruffalo said he was most influenced by the stories Forbes told him about her father, who died several years ago.
Because her father was unable to keep a job and her mother was in school, Forbes grew up with very little, which was even more painful because her father's family was wealthy but shared nothing, she said.
Forbes said that even if she's happy she made the film, it wasn't always easy filming it. Because medication was such a random science in the 1970s, her father was sometimes unrecognizable as his true self, particularly when he was hospitalized.
"The scenes in the hospital were incredibly difficult to shoot," she said. "I felt like a little kid again."
PHOTOS AND MORE
PHOTOS: Faces to watch 2014 | Movies
ENVELOPE: The latest awards buzz
SUNDANCE FILM FESTIVAL: Photos, features and video