For his first appearance at San Diego Comic-Con, Oliver Stone told an audience at the convention’s biggest venue that he almost hadn’t been able to make his upcoming movie Snowden, based in part on Guardian journalist Luke Harding’s book about NSA whistleblower Edward Snowden, The Snowden Files.

“Frankly, it was turned down by every major studio,” Stone told the audience. “It was definitely self-censorship. I don’t believe there was an enemy such as the NSA lurking in the background but self-censorship is a huge issue in this industry. Every film studio, the boards, rather than the executives, said no.” The film is being distributed by five-year-old independent production company Open Road, which swept the Academy Awards with its film Spotlight earlier this year.

Answering questions after a brief trailer – and an instructional slide showing attendees how to cover their laptop cameras with a bandage – were Stone, Joseph Gordon-Levitt, who plays Snowden, Zachary Quinto and Shailene Woodley. With Gordon-Levitt, Stone and his co-writer Kieran Fitzgerald visited Snowden in Moscow to research and develop the film; Stone said he hadn’t wanted to make the movie at first because litigation has been such a problem when dealing with contemporary topics.

“I really didn’t want to do this at first,” Stone said. “You get beat up when it’s current. You get killed with lawsuits. Often the protagonist of the movie will turn on you. This story’s not over yet, we’ll see when it comes out, but I’ve been hopeful that it’s been smooth.”

In addition to Harding’s book and Snowden lawyer Anatoly Kucherena’s roman á clef The Time of the Octopus, Stone said he modeled parts of the film on George Orwell’s seminal novel about surveillance and totalitarianism, 1984, notably a bureaucrat played by Rhys Ifans who Stone said was based in part on the novel’s Inner Party member O’Brien.

Woodley said she had “never been very politically active before this election”, but that Snowden’s whistleblowing had inspired her. “[He] really opened my eyes to policy in a way I’d never thought about before,” she said.

Of course, it was still Comic-Con. After a few serious questions about Manuel Noriega and international turmoil during the Reagan administration, one audience member asked whether the convention-goers should be worried about Pokémon Go, and after his time at the microphone, a man in a homemade uniform with his hair curled up creatively over the top of his head introduced himself to the audience and the panel as Prism.

“My name is Prism, and I didn’t have to come to Comic-Con because I was going to be here already,” he said. He was wearing a Google Glass headset, he explained, because the NSA hadn’t been as successful as it had hoped in getting the public to adopt the always-on video technology.

Kidding aside, said Gordon-Levitt, suggestions that the movie’s production difficulties had anything to do with government surveillance miss the point. “The NSA isn’t trying to proactively stop us from making a movie, it’s more subtle than that,” he said. “It’s about how you change your behavior when you know you’re never alone.

“The question is not about whether you need privacy or whether you don’t need privacy; we’re promised privacy in the constitution and if the government is going to change those rules they need to be open and honest about that.

“That decision wasn’t made out in the open. It was made in secret, and then lied about.”

The events dramatized in the film were written about extensively in the Guardian, which received a Pulitzer prize for its coverage in 2014.