SEATTLE FILMMAKER LYNN SHELTON’S Humpday, her third feature, screened last January during the opening weekend of the Sundance Film Festival and by the following Monday had landed a national distribution deal with Magnolia Pictures—this for a locally shot movie about two straight guys who wind up in bed with each other as part of an amateur porn contest.

“We were the first film to show in competition,” Shelton recalls. “I was terrified because there was so much buzz about it and I wasn’t sure what people were expecting. I knew the premise could have people thinking they would get something that they weren’t going to get. But within an hour after the screening people were screaming across the street to each other, ‘We love Humpday!’ One of my proudest moments at Sundance was being at Whole Foods and this very conservative-looking grandma who knew I’d made the film came up to me and said, ‘I never thought I would have found myself in that theater.’ But then she went on and on about how much she liked the film.”

The movie debuts in its hometown on June 5 as the Centerpiece Gala of the Seattle International Film Festival before a wider release in August.

Shelton grew up in Seattle and got a University of Washington theater degree before moving to New York, where she received an MFA in photography and related media from the School of Visual Arts. Her thesis project was a movie and, after experimental filmmaking and editing corporate commercial work, she focused firmly on a career behind the camera. She moved back to town in 1998 with her husband, who’s from Bellevue, and has since then made all of her films here.

“For years, I made films about the female experience because they say write what you know,” she says. Her first feature concerned “a 23-year-old woman who had lost her sense of self.” Documentaries included The Down of Her, about a woman’s relationship to her body hair: “All the work that I was making was from the inside out. But at the same time, I’ve always been a close observer of people. And then from the skill set that I’ve developed as a documentarian I was able to work from the outside in.”

Although Humpday ’s premise raises eyebrows, Shelton promises something with more depth than Hollywood’s “bromance” buddy films (The 40-Year-Old Virgin, I Love You Man, et al). A “fully fleshed-out” female character figures prominently in the proceedings. And the men provide the source of comedy in her film more than their awkward predicament. “What these two guys end up doing is boxing themselves into a situation where they’re basically trying to out-dude each other,” she explains. “You end up laughing at the extremities of their straightness, their constant one-upsmanship. It’s about the identity crises that these two men inspire in one another. It really isn’t about what it seems like it’s going to be about. It’s more nuanced. We felt like the movie wasn’t going to work unless it was believable every step of the way, so we wanted to make sure that you would buy every ridiculous thing that happens.”

The film isn’t Shelton’s first gaze at tensions in male relationships. Her last movie, My Effortless Brilliance, contemplated what she calls “a breakup between two platonic friends” and won her a Someone to Watch honor at the 2009 Independent Spirit Awards. So, yeah, 2009 has been a great year for her. Tinseltown must be awfully tempting after toiling so long in the Emerald City.

“I don’t have any interest in moving away,” Shelton says. “I’d love to be able to make all my films here. I have this great quality of life and, in a way, I don’t want to screw it up. I’ve been able to self-produce in a really cheap way so I’m not waiting around to be given permission to make a movie. At the same time, yes, I’m interested in seeing what Hollywood has to offer—although I’m wary.”