For director Duncan Jones, it was easy to pinpoint the highlight of Monday’s premiere of Summit’s “Source Code” at the ArcLight Dome.

“I loved how everyone gasped when Jake Gyllenhaal jumped off the moving train,” Jones mused at the afterparty at Boulevard 3. “That’s what you live for as a director.”

Jones shot the entire pic in 36 days — including a spectacularly sunny day in Chicago in February 2010. “That’s about as lucky as you can get.”

Vera Farmiga said she was struck by how much has changed for her since the “Source Code” shoot.

“I was four months’ pregnant, which you can’t tell because I’m in a uniform and behind a desk, but since then, I’ve had a baby and directed a film.”

Screenwriter Ben Ripley said the spark for the circular story came from a surprising source. “I started writing this about four years ago after I was inspired by ‘Groundhog Day,’ ‘Rashomon’ and other nonlinear films. I needed to have a lot of two-hour conversations with my manager to figure it out.”