Looper may be an action-packed science fiction thriller, but it's also got smarts and heart, according to the director and stars of the TIFF-opening film.

"That's what I want out of going to the movies. I want a fun time, but I want something to talk about when it's over," lead actor Joseph Gordon-Levitt told a packed room of international media gathered for the first day of the Toronto International Film Festival.

"I like to have something to have a conversation about, something to think about, something maybe I'll keep thinking about for a while and Looper has got both those sides."

Inspired by writers like Philip K. Dick and Ray Bradbury, movies like The Terminator as well as old westerns, Looper is the product of a long-gestating idea that writer-director Rian Johnson first discussed with Gordon-Levitt back in 2003, after they completed the teen noir Brick, their first film together.

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Looper stars Joseph Gordon-Levitt, left, and Bruce Willis, centre, pose with director Rian Johnson at the 2012 Toronto International Film Festival on Thursday. (Aaron Vincent Elkaim/Canadian Press)

Set in a dystopian U.S. in the near future, the time-twisting tale follows an aspirational mob hitman (Gordon-Levitt) faced with a dilemma when presented with his latest target: an older version of himself (Bruce Willis) sent back in time.

According to Johnson, the goal was not to get bogged down in complications like explaining exactly how time travel works, for instance, but to create a story that took "what I love in science fiction, which is using a twisty magic trick of a sci-fi plot — using this kind of weird magical thing of time travel — to set up a very human situation.

"For me, Ray Bradbury was a master at that: using an outlandish sci-fi thing to do something that just stabs you in your heart and leaves you sobbing at the end of a short story. That's what great sci-fi can aspire to," Johnson said. "I saw the potential to try and do that."

Willis said it was the quality of the script as well as its emotional heart that drew him in, citing his tender, romantic scenes with Chinese actress Summer Qing (playing his wife) and the intensity of his close-up exchanges with Gordon-Levitt, who studied Willis' past performances for the role and wears contacts and prosthetics to more closely resemble him. He was also surprised at the finished product.

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Bruce Willis appears in a scene from Looper. (Alan Markfield/Alliance Films)

"When shooting the film, I never thought I was doing anything wrong, as my character," the Hollywood action icon noted. "When I saw [the finished film], I was emotionally moved by how horribly wrong [my character's actions were]

."

That said, both he and Johnson emphasized that the darker nature and violence in Looper is something that is essential to explore on film, despite some criticism of movie violence since the Colorado movie theatre shooting this summer.

"Violence is one of the hard, bad things that exists in the world, not just in films, it's everywhere," Willis said.

"To take one thing out, to say you shouldn't have violence in film or we shouldn't make violence part of a film, would be like taking an emotion out of it."

"Movies can serve as a great warning," Gordon-Levitt added.

"I like when a movie has something to say and can point out certain things we don't notice every day, about our world, about ourselves. I think that's the purpose of telling stories.... It's all in service of learning about ourselves right now. Every really good movie does that."

The Toronto International Film Festival continues through Sept. 16.