The last time writer-director Stephen Gyllenhaal visited Seattle to promote a movie, the picture was "Homegrown" (1998), a Billy Bob Thornton vehicle about pot farmers that eventually became a hit on DVD.

But he was almost more excited about the fact that his 17-year-old son, Jake, had just landed the starring role in "October Sky" (1999). More than a decade later, Jake has become an Academy Award nominee for "Brokeback Mountain" (2005), while his sister, Maggie, earned an Oscar nomination for "Crazy Heart" (2009).

As proud as he is of their accomplishments, Gyllenhaal won't be directing either of them anytime soon. Jake turned up for a few seconds in "Homegrown," but it's strictly a cameo role.

"I've made a really clear decision in my life not to work with my kids," Gyllenhaal said when he brought his new political comedy, "Grassroots," to the Seattle International Film Festival a little over a week ago. (The film returns to Seattle for a regular run on Friday, June 22.)

"It's a big enough job to be their parent and grandparent to their children without bringing in the agenda of working with them," he said. "And they're doin' just fine without my help at this point.

"It's a joy just watching them work, but ultimately my relationship with them is as their dad. I get to hang with them for real, and that's where my real pleasure is — as with any parent finally. I have to say it's fun to be a grandfather, still making movies."

At 62, he has plenty of projects to keep him from thinking about retirement. He spent 13 years preparing "Homegrown" and about five years for "Grassroots," a Seattle story that was actually shot here.

"It takes a long time to make a movie," said Gyllenhaal . "You go down a lot of wrong avenues, then kinda come back, you know. You don't build a building overnight, and you don't make a movie overnight either."

The script for "Grassroots" is based on "Zioncheck for President: A True Story of Idealism and Madness in American Politics," Phil Campbell's 2005 book about a 2001 Seattle City Council race. In that election, political upstart Grant Cogswell challenged incumbent Richard McIver in a quixotic bid to extend the monorail.

"I was drawn to the book because there were two very human slacker characters" — Cogswell (played by Joel David Moore) and his manager (Jason Biggs) — "who jumped into a campaign for generally the wrong reasons, but then in the process grew up.

"As with filmmaking, ultimately, politics, and being involved with politics, demands growing up," he said.

"Disappointed by what's happened in the White House? I kinda want to say, 'Grow up; this is a tough process. Jump in, don't get cynical, don't take the easy way out, participate in the process' — which is why I made the movie, to some degree."

Working on the script with co-screenwriter Justin Rhodes led to location-shopping.

"Seeing the monorail, that really began to infuse another level of energy," Gyllenhaal said. "Riding the monorail that first time was kind of ... whoa ... this makes sense; it's not a crazy idea. But it can be played in a kind of wonderfully comedic way — which is what I was looking for, too."

To that end, Gyllenhaal cast Cedric the Entertainer as Richard McIver.

He hopes the movie puts the spotlight on grass-roots politics as well as Super PACs, and the millions of dollars that go into 21st-century campaigns.

"How can you bring about the change that people on Main Street really want? And do it with a sense of humor? I have a serious agenda. I think comedy always has a serious agenda behind it, but you damn well better laugh, or you're dead."

John Hartl: johnhartl@yahoo.com