While the screening of "Trainwreck" that debuted at the South by Southwest Film Festival in Austin, Texas, back in March was designated a "work-in-progress screening," it was so fully formed, so hilarious, so brilliant and explosive and heartfelt, that it felt finished and ready to capture the national zeitgeist, which it will undoubtedly do when it's finally released this summer. Sometimes you see a movie and just know that in a few months everyone will be talking about it. "Trainwreck" is that movie.

"Trainwreck" stars and was written by Amy Schumer, who plays a journalist living in New York City that, as the title suggests, doesn't exactly have her act together. She's sleeping with a sensitive meathead (John Cena), while also drinking heavily and, well, sleeping with a bunch of other people as well. But an assignment to profile a sports doctor (Bill Hader) that turns into a really-for-real romance, coupled with the declining health of her father (Colin Quinn), forces her to rearrange her trainwreck-y ways and grow up a bit. It's both hilarious and emotional, directed with grace and verve by Judd Apatow (this is the first film he's ever directed that isn't based on one of his own scripts).

So it was a real thrill to get to sit down with Apatow and Schumer in Austin to talk about the movie, how it might change before it reaches theaters, the amazing supporting cast (seriously, this includes everyone from Ezra Miller to Method Man to Dave Attell to LeBron James to Tilda Swinton), variations the script went through and whether or not they'd reteam for more projects. And yes, there was lots of laughter.

Moviefone: What sparked that initial fascination in Amy's script and, Amy, what made you think Judd was a good fit for the material?

Judd Apatow: I wanted to do something with Amy. I wasn't sure what it was. For half a year Amy wrote a completely different script, which was really funny but I kind of sensed -- and maybe it's from working with Lena [Dunham] and seeing how deep she goes -- but I felt like it wasn't the right first movie for her. The stories she was telling me from her life should be in this movie. So we just had a long talk about that and I asked, "What's really happening? What's happening in your relationships, for good or bad? What are the obstacles?" And then this idea formed very quickly and Amy was really great about including deeply personal aspects of her life in the movie. I have that conversation with people all the time and they, "I don't want to put that in a movie because my family will get mad or my ex-boyfriend will get mad." And it just stops.

Amy Schumer: It felt like such a dream come true. I can't think of anyone whose sensibilities match up better with mine. It was like fantasy camp. It's unbelievable this has happened to me. Three years ago I was at a Funny Bone in Indiana begging to get half off of wings.

Apatow: Did you get it?

Schumer: No! I didn't get it! But I think that Judd's sensibilities are my favorite kind. I love people who can make you laugh really hard and then be gutted the next second and he's so good at finding that balance. Some of the scenes are a little heavier and we needed something to break the tension, which were things I didn't understand because I had never written a movie before.This is a movie with a lot of firsts -- Amy, it's your first movie, and, for Judd, it's your first movie set in New York and your first movie written by somebody else. What was that adventure like?

Apatow: Well, it was great to shoot in New York. I haven't lived in New York for an extended period of time since I was living in Long Island as a kid. I never lived in the city. So just that experience was so much fun; it got me jazzed. Is that a young word? Jazzed?

Schumer: Oh, that's very hip. Too hip!

Apatow: And I was watching Amy, who through this whole process would do stand-up every night and do concerts and so every night after shooting I would go to the Comedy Cellar. That really woke my brain up comically, to try and do that at the same time, waking up circuitry. It was a very special experience making the movie and just seeing how hard Amy was working. Most people don't work that hard. I say that all the time and nobody ever listens to me. I say that the people who do well just work really hard. I would give notes to Amy and she'd bring a new draft back 8 days later. Most people would take three months or never bring it back.

Schumer: They just avoid you at parties. "Oh god, he's here."

Apatow: So that was really fun and it was fun not being the writer on it, since it gives me a perspective. I could read her page, I could pitch things but it takes away some of the terror of being completely responsible for all of the writing, directing, and producing. It's a lot to take on. So I think it allowed me to be fresher and allow me to guide her into an area. But then she had to go off and figure it out. I would go take a nap.

Schumer: There's been no napping for me for two years. It was a lot, because I was also editing the second season of my show, doing stand-up on the road, and just re-writing this draft a million times. I think it's the hardest I'll ever work. I hope so...

Would you write another script for him?

Schumer: Of course!
Can you talk a little bit about casting?

Apatow: It was fun to be in Amy's universe and to be in this east coast space. I love Colin Quinn, as does Amy. I met him when I was in my early twenties when he was doing "Remote Control" and he was one of the first people who was really kind to us and hilarious. So I've known him forever. And I loved what he did on "Girls." So when Amy said that she wanted Colin to play her dad, I thought, If he can appear old enough, that's a fantastic idea. It's really populated with a lot of people from the New York comedy scene -- Saturday Night Live" and he totally got the joke and was improvising and totally prepared and loose. It's not a spoon-fed performance, it's actually an enormous amount of his personal decisions and jokes. He's just very prepared to give it his all.

Were you thinking of these people when you wrote it -- like Tilda Swinton?

Schumer: Well, I wrote it for her as a complete hypothetical, like LeBron. I wrote in the script, when I described her, as "like Tilda Swinton waiting in a baggage claim." Because I had seen her once at a baggage claim and thought she was the most elegant, strong woman. Judd had met her years ago and said, "Oh, we should work together." So the fact that those two pieces of casting worked out is just mind blowing. I couldn't believe it. When I would be doing scenes with her, I was trying to be perfect but I kept thinking, Tilda Swinton, Tilda Swinton, Tilda Swinton...

Apatow: And Brie Larson we had written a big scene for in "Bridesmaids." We had written this big sequence in Vegas but a lot of comedy movies, like "The Hangover," had scenes set in Vegas so we cut the sequence out. So we were excited to get a chance to work with Brie; I had been a big fan of hers since she was on "United States of Tara."
And Bill Hader gives such an incredible, unexpected performance.

Schumer: Right? I can't imagine getting to work with somebody better. He was so amazing and I felt so supported and encouraged every day by him. He's just the funniest guy. And that was Judd -- Judd has seeing him as a leading man, so I have to give full credit to Judd on that. It worked out for me.

What was the most surprising aspect of this movie?

Apatow: Well, it was great to see what a strong actress Amy is. And the difficult scenes that were more emotional, it wasn't hard to execute that. She was so well-prepared and she knew what she wanted to do; it was more about giving her the space to get there. You never really know how the more difficult scenes are going to work. Amy really knows what she's doing. So at the beginning of the shoot it was like, Oh wow, we can really go there! Because Amy is ready to play and has been preparing for this her whole life. I don't know how many movies you had been in, even in tiny parts.

Schumer: Two...

Apatow: Well, what's interesting is usually when someone gets the lead part, they say, "Well, I played the friend in 25 movies." This really was, in a way, Amy's first movie, and she's doing everything. To me that's really exciting because a lot of it is trying to crack the code of how someone is as the lead. You can make a great movie but it's a little less interesting if it's somebody's 40th movie. But when it's someone's first movie you have to really work on how to present them.

So now he's not interested in making any more.

Schumer: No. He's not even looking at me.

Can you say what the final version of the movie will look like versus what we saw at SXSW?

Apatow: Well, it's almost like the final testing, because we're still listening to jokes. There was one scene that we had never had in there before -- the scene in the bathroom where they're talking about Johnny Depp. Did you like that?

I did!

Apatow: Great! Then we're done.

"Trainwreck" hits theaters everywhere July 17.