The first 22 minutes of the Stephen King adaptation “The Long Walk” debuted at San Diego Comic-Con on Friday, following the debut of the new red-band trailer and a panel featuring the cast, including Mark Hamill, David Jonsson (“Alien: Romulus”), Tut Nyuot (“Small Axe: Red, White and Blue”) and Garrett Wareing (“Manifest”).

The film is adapted from King’s 1979 novel (first written when he was 19!), set in an authoritarian America in which 50 young adult men join a televised contest to walk continuously at a pace of at least three miles per hour — or they’ll be killed. Hamill plays a man only known as the Major, the military commander who oversees the Walk and gives the walkers their literal marching orders. In the panel, Hamill said that when director Francis Lawrence approached him about playing the part, it immediately evoked his teenage years in Japan, where he went to school next to a U.S. military base.

“I said, ‘I know who this guy is: I’ve seen him firsthand,’” Hamill said. “I’d walk across the parking lot, seeing the officers putting these guys through their paces in blazing hot sun, and they were just brutal. Like if you vomit, they force you to eat it. It’s horrible.”

The role is the latest in a series of darker, more complicated roles for the man indelibly known as “Star Wars” hero Luke Skywalker. The actor said that around 2019, he decided he wanted to step away from acting on camera.

“I thought this stage in my career, I’d be spending more time with a metal detector, wandering around the beach, playing with the dogs in the backyard,” Hamill said. “I said to my agent, ‘You know what? I’m not motivated anymore. I think I’m gonna just sort of retire and just do voice over.’ And the only people that rejected were my agent and my wife, because, you know, it’s good to have me out of the house.”

He credited filmmaker Mike Flanagan for reviving his career by casting him in his Netflix series “The Fall of the House of Usher.” “That would have been a routine character for voice over, but to play an amoral, sociopathic lawyer, just pure evil — never on camera,” he said. Flanagan then cast Hamill as an alcoholic accountant and grandfather to the title character. 

“What a turnaround!” he said. “I didn’t expect to be this busy.”

Earlier in the panel, screenwriter JT Mollner discussed how happy he was to keep the “heavy, exciting, terrifying themes” of King’s novel. “We so wanted to make sure we had the beauty and love in the story of friendship — and also the brutality, hopelessness and terror,” he said. “I’m very very grateful that we could keep the teeth that the book has.”

That’s as far as anyone in the panel addressed the film’s parallels to the current dire state of American democracy. Instead, in a taped segment, Lawrence and “Long Walk” actor Ben Wang — currently in production on “The Hunger Games: Sunrise on the Reaping” — discussed how the grueling nature of the shoot, in which the actors walked for miles on a Canadian highway, created a strong connection between the cast. 

“We shot this movie chronologically,” Lawrence said. “So as everybody got together and met for the first time [in the movie], you as actors were meeting for the first time and becoming friends, and then going on this experience together. The physicality of this job of walking sometimes 30,000 steps a day doing these very, very long takes, I think created a bond.”

Then Lawrence surprised the crowd in Comic-Con by announcing that they were going to watch the opening act of the movie, which ran from when the lead character, played by Cooper Hoffman, arrives at the Walk and meets the other walkers, to the moment (teased in the trailer) that the first walker “gets his ticket” — the Major’s euphemism for getting killed.

“The Long Walk” will premiere on Sept. 12.