Starring Joaquin Phoenix. Rated 14A

The late cartoonist John Callahan was an orphaned screwup and committed alcoholic who never found his creative feet, as it were, until a drunken car wreck confined him to a wheelchair.

Robin Williams was originally slated to play Callahan, but never followed up with experienced director Gus Van Sant, who adapted a grab-bag script from the cartoonist’s memoirs. Instead, Joaquin Phoenix—despite looking nothing like the ginger-haired, pale-skinned subject—delivers one of his most generous performances in a physically constrained role, as a quadriplegic with limited use of his arms.

As depicted in scenes that jump rapidly back and forth through time, Callahan initially uses his hands to, well, keep opening bottles. And also to slam his powered chair down the streets of Portland, Oregon, a city that he shared over the years with Van Sant (seen as a backdrop in breakthrough films like Drugstore Cowboy and My Own Private Idaho). Eventually, Callahan finds support in an AA group run by an almost unrecognizably slim and longhaired Jonah Hill, as a gay, snarky trust-fund kid who tells it like it is.

Sonic Youth’s Kim Gordon and Euro-indie veteran Udo Kier play cynical ex-addicts in the group scenes, which start out strong, but quickly grow repetitive. After a solid near half-hour putting the pieces in place, Don’t Worry, He Won’t Get Far on Foot (a title taken from one of Callahan’s mordant cartoons) runs into a rut for another 90 minutes, with two-character confrontations plowing through the same information again and again. Some attempts are made, rather obligatorily, to integrate Callahan’s transgressive cartoon humour with what becomes a fairy tale of sentimental uplift, minus the bedsores and respiratory problems that eventually got the guy, at age 59.

In his work, he relentlessly mocked his own disabilities and people who defended their notions of the disabled, at a cost to friendships and syndication. (Callahan remained popular in National Lampoon and Penthouse Forum.) There are a few jarring moments, as when a sexual-rehabilitation specialist tells him to ask his nurses if they’d care to sit on his face! Elsewhere, this generally sunnier vision is taken to absurd levels with the introduction of Rooney Mara as a Swedish flight attendant and volunteer therapist who eventually marries him. But her part remains a gauzy fantasy, unconnected to the main story.

The real Callahan also taught himself to play the harmonica and ukulele and wrote whimsical ditties. Why is such an obvious asset missing from a movie notably lacking in variety and surprise?