"I think I need to take my clothes off."

That's what Olivia Wilde told director Joe Swanberg at one point while shooting her latest movie "Drinking Buddies." After the movie's premiere at SXSW this weekend, I had a chance to talk with Wilde, Swanberg, and the rest of the cast during a private meet-and-greet.

Swanberg has become something of an institution at the festival for making a string of sharply realized character studies like "Hanna Takes the Stairs" and "LOL." "Drinking Buddies," which also stars Jake Johnson, Anna Kendrick, and Ron Livingston, is his biggest budget, most accessible movie yet.

The trick to his films is that they are completely improvised; he collaborates with his actors to figure out everything from the dialogue to major plot points. No set script. No marks to hit. It's a method that actors find both daunting and liberating. "I was scared sh-tless," confessed Kendrick.

"After you improvise for a while," recalled Wilde, "you can't remember what you've done. It's so instinctual; it's flowing out of you. It almost feels like you blackout."

"Drinking Buddies" is about the increasingly ambiguous relationship between Wilde and Johnson, who work together at a Chicago brewery but edge closer and closer toward something physical, in spite both of them being in relationships with other people. During a late night at the beach next to a fire, Wilde strips down and jumps into the Lake Michigan, hoping that Johnson would follow.

Though Wilde is no stranger to onscreen nudity -- check out "Alpha Dogs" -- this is the first movie in which she suggested it. "I think [her character] Kate goes skinny- dipping," she said to Swanberg while shooting the scene. "That was something that came totally organically when we were sitting by the fire."

Johnson then chimed in, recalling, "If you remember in that moment, I go I think [his character] Luke is going to jump in that water with her. She's running naked. Luke's gotta take his clothes off, too." Though Swanberg improves his movies, all the actors reported that he had a very clear vision for the arc of the film. Johnson doffing his duds wasn't a part of that vision. "Damn you, Swanberg," joked Johnson.

The emotions raised on-set frequently blurred the lines between what's real and what's in the movie for the actors. After shooting a nasty fight scene, both Wilde and Johnson felt really unsettled.

"After the fight scene, I texted Olivia and said 'Are we good?'" said Johnson. "I was with my brother and nephew in real life, and I said I have to go into the other room and they said why. And I said, because this movie is weird. It's f--king with my head."

And since the movie takes place in the world of craft breweries, Wilde and Johnson spent a lot of time hanging out at an actual brewery, talking with the people who work there, and learning to brew beer. "We wanted to learn as much about it as we could," said Wilde. They also drank an ungodly amount of beer. "The shoot was a 20-day bender," joked Johnson.

"Drinking Buddies" will hit the theaters later this year.