Deftly avoiding easy chuckles or a patronizing pitch of a tongue-wagging premise, “Humpday” — the tale of two straight buddies who decide to make a movie for a porn film festival starring themselves having sex with each other – is a smart, amusing, and veracious film. The clever, meaningful script, a commendable cast, and the intelligent approach from director/screenwriter Lynn Shelton guarantee that the main plot thrust is not merely a contrivance for this pleasurable flick.

In the middle of the night, Andrew (Joshua Leonard) knocks manically on the door of the surprised Ben (Mark Duplass), a college buddy, and his perplexed but understanding wife, Anna (Alycia Delmore). The unannounced visitor fresh from Mexico is an exuberantly over-the-top dude who’s ecstatic to see his college friend of a decade earlier, ostensibly because he believes that Ben can be cajoled into teaming up for the globe-hopping dharma bum’s local escapades. The presence of the seldom heard from, itinerant traveler unsettles Ben, married, mortgaged and with plans for a child. Upon Andrew’s invitation the next day, Ben arrives after work at Dionysus, a communal house inhabited by free spirits that Andrew just happened to run into during his meandering around town. Ben is both discomfited and intoxicated by the slackened boundaries of the throng. (He blows off Anna’s earnestly prepared pork chop dinner for mung bean sprouts, and booze, and, oh, weed, and, ah, sex talk with strangers.) Shooting the shit becomes effusive artistic inspiration. Reunited, and feeling so good, Andrew and Ben reach Level 3, the degree of inebriation coined by comedian Larry Miller where “you love the world” and alcohol (and more) fuels cordial, soused inspiration. “It’s where,” Miller muses, “you try to convince your friends that you could open your own bar, and everyone could live together, yeah Tommy you could cook.” Instead of applying for a liquor license, the duo enthusiastically convinces themselves to enter a project in the Seattle alternative weekly newspaper The Stranger’s annual HUMP! porno film festival-cum-contest.

Filled with witty, believable dialogue, the conservations in “Humpday” carry a natural rhythm with gentle interruptions and speakers forming thoughts as they speak. Each of the three main characters has the time to talk, or sputter, or just toss their ideas out as though they were engaged in an important but informal brainstorming therapy session. (Shelton’s script is very funny, and at times hysterical, but not a joke. And the conversations are shot astutely by cinematographer Benjamin Kasulke and particularly well edited by Nat Sanders.)

As the film progresses, the gradations of the characters’ personalities are exposed and the full-bodied chats illuminate insights. While Ben and Andrew contemplate how to proceed with their artistic endeavor, they discover in their reacquaintance that each is more complex than first imagined. Ben tells Andrew that he is “not as Kerouac” as he believes himself to be; Ben then stresses that he is “not as picket fence” as Andrew perceives. (Andrew betrays his Beat Poet facade back at Dionysus when he hastily puts his clothes back on as his bisexual love interest and her lesbian lover bring massive rubber cocks into the threesome’s bed.)

When Ben, in a strong performance from Duplass, who with his brother Jay is the writer/director of “The Puffy Chair” and “Baghead,” finally stutteringly shares with Anna his reasoning for wanting to press forward with the film, her rationale for agreeing is revealed as well. There’s the clear sense that Anna would rather deal with the reality of her husband’s proclivities and the repercussions than insist he not go forward and somehow drive his desires underground. It’s not resignation but resolve, and, besides, Anna (in a fine feature-film debut from Delmore) gets to make an unburdening confession of her own. (Shelton has an eye for a nice visual touch as well, such as when Ben prepares a dinner to break the news to Anna and carefully adjusts the olives in the salad just so.) Leonard, especially, grows into his role as Andrew. At first a zany, sexy dervish, he captures the nuances of a character who is ultimately quite tender if not prudish, and expresses Andrew’s vulnerability just as the camera is about to roll on their film by noting that he is an intrepid explorer but “You don’t have to have a hard-on to bungee jump.”

“Humpday” reaches its climatic jumping-off point with the “will they? won’t they?” voyeurism handled maturely and affectionately. Shelton has created a sincere and genial film which could be warmly subtitled Bromancing the Stoner.