Al Pacino broods through “Manglehorn,” an intimate drama about a lonely locksmith who lives, if you can call it that, in a small Texas town.

As title character A.J. Manglehorn, Pacino is on screen in nearly every scene. When he’s not on a locksmith call, Manglehorn is often the only character shown. He exists in his cluttered workshop, surrounded by keys, and in a small house with his only companion, a fluffy white cat named Fanny.

Director David Gordon Green’s previous work includes the similar but more satisfying “Joe.” That film starred Nicolas Cage.

In “Manglehorn,” Green dwells on his principal character’s obsession with a long-lost love. The film finds its melancholy poetry there.

Every day, Manglehorn writes letters to a woman named Clara. Moviegoers hear the sadly hopeful words via Pacino’s voiceover.

“I made so many mistakes,” he writes. “And now I look around and everything is gone. Why didn’t I stay with you? I’m a fool. The only thing I want to do anymore is love you.”

In another of his daily rituals, Manglehorn checks his bee-infested mailbox for letters from Clara. The post office returns his letters unopened, stamped “Return to sender.”

Written by first-time screenwriter Paul Logan, “Manglehorn” competently goes about the business of establishing its antihero’s mundane routines.

Manglehorn works with some enthusiasm when he opens people’s accidentally locked car doors. Other than that, he dines alone at a local cafeteria, speaks affectionately to his cat and goes to a bank on Fridays, mixing business with a little social interaction.

A few moments of small talk with Dawn, a bank teller played by Holly Hunter, are the highlight of his week.

As Dawn, Hunter, a wonderful actress who’s done more TV lately than film, brings some joy into Manglehorn’s life. Likewise the movie.

Unlike Manglehorn, Dawn isn’t pining away in fantasy, not dreaming an impossible dream about the past.

A film about Dawn, featuring Manglehorn as a supporting character, might have been much more interesting.

The movie tries but fails to make Manglehorn a more sympathetic figure. These attempts are made largely through another interesting supporting character, Gary, a tanning salon/massage parlor operator played by Chris Messina.

In hallucinatory scenes that clash with the grim reality of Manglehorn’s other waking hours, Gary revels in memories of what a magical baseball coach Manglehorn was decades ago. The potential in such stories gets lost because they’re merely told, by Gary, rather than shown.

Some day a deep and engaging movie about a sad old man who longs for a woman he knew 40 years ago may be written and filmed.

The downbeat “Manglehorn,” even with the ever-watchable Pacino in the lead, isn’t that movie.