He wrote the script partly while shooting an “Ocean’s” movie in Europe and partly while living in Hollywood’s famed Chateau Marmont hotel. While he is mindful to downplay the script’s autobiographical elements, it is likely no coincidence that Scott Caan has written himself a part as an emerging literary talent.

The Caans have been circling the idea of appearing together for some time, not so much opposed to the notion as waiting for just the right material.

There have been projects they have turned down, and Scott Caan previously wrote a script for them that remains unproduced. James Caan had a small part in Scott Caan’s directorial debut, but it didn’t make the final cut

“I’ve been very lucky in my life,” said James Caan. “I’ve done, like, 80 pictures, and I’ve never been cut out of a movie — except Scott’s. Completely cut me out of ‘Dallas 362.’ My own son.”

James Caan shot only a couple of days on “Mercy,” and when it came time for them to shoot the biggest emotional scene between their characters — an attempted reconciliation in which a lonely father dispenses hard-learned life lessons to his son — things got off to an odd start. Because of a mix-up in call times, James Caan arrived in the morning at his son’s L.A. house, the location for that day, 12 hours early.

The two happily spent the day together, and when it really was time to shoot there was an air of anticipation about whether the real father-son dynamic would translate to their fictional characters.

“It was weird, it was uncomfortable,” recalled Scott Caan, whose parents divorced when he was young. “It was impossible to avoid the reality of how we really feel for each other and what was really going on. So for me, I’m in a scene with my father where a lot of that relationship is made up. And it was hard to portray that we were not close and that we didn’t have a good relationship. I can’t deny that camaraderie that we have in real life, and as the writer I’m thinking, ‘that’s not what this is, our characters don’t get along.’ “

It is inevitable that those watching the film will want to assume the scenes between the Caans older and younger are somehow a reflection of their relationship or that Scott Caan is somehow working out his unresolved feelings toward his father. Not so, he insists. Well, not quite, anyway.

“I don’t care about that,” Scott Caan said matter-of-factly. “People say what they’re going to say anyway. And some of it is true, some of those feelings are there. I couldn’t have written it unless something was real about it.”

For James Caan the issue wasn’t so much how art reflected life or vice versa but rather just turning in a solid performance.

“I’ve worked with Francis Coppola, Howard Hawks, some really wonderful directors,” he said. “And I never was so scared as those couple days on ‘Mercy.’ It’s all right to fail, but what if you fail for your own son? Can you think of anything worse?”