TORONTO — Actress Elizabeth Banks was prepared to be naked, although she was hoping director Kevin Smith would block her breasts with something, perhaps Seth Rogen’s “big head” with its crown of curls.

Banks, co-starring in “Zack and Miri Make a Porno” told a table of reporters, “I mean, Seth shaved his back and I did a little body tanning and we were ready to go, and then Kevin kind of had this epiphany, like you know what? Actually, it’s going to be this other thing, and I think it was absolutely the right decision for the movie.”

The resulting scene is one of Banks’ favorites in the R-rated romantic comedy shot in Pittsburgh earlier this year. “It breaks my heart whenever I see it. I really just felt like Miri’s heart was just bursting open in that moment.”

“Zack and Miri” had its world premiere at the Toronto International Film Festival before a wildly enthusiastic, packed house. The movie opens everywhere on Halloween, although Smith will be in Pittsburgh this weekend for a single sold-out show at the Oaks Theater.

Banks, a 34-year-old Massachusetts native, is having the autumn of her life, or at least her career, as she talks dirty, plays demure and gets involved with role models, good and evil. In addition to “Zack and Miri,” she is Laura Bush in “W.,” plays Paul Rudd’s girlfriend in “Role Models” (from David Wain, who cast her in “Wet Hot American Summer”) and is an evil stepmother in “The Uninvited,” a remake of a Korean horror film opening in January.

“I feel, for the first time in my life, that I can say no to things and I don’t worry that it’s over, like I’ll never work again. I think every actor thinks, ‘If I pass on this, I may never get another offer.’ I think for the first time in my life I can be selective.”

Volunteering and occasionally proving that she swears like a sailor and has no problem talking about a particular female body part, Banks said she never flinched at Miri’s dialogue. “I think it’s a generational thing, partially, and look, Mae West went for it, and there have been many other women who pushed the envelope.”

Although Smith had written the role of Zack for Rogen, he had Rosario Dawson in mind for Miri. When she was busy with “Eagle Eye,” Banks emerged as one of a half-dozen actresses who were available and might be inclined to like the material, which was spot on.

“The two had such amazing chemistry together,” Smith said. “They bounce off each other. That dude is an organic comedy machine, and that could be intimidating to stand opposite and try to act against, but, man, she more than held her own, she was able to give back as good as he gave.”

The leads are supported by adult film actresses Katie Morgan and Traci Lords and Superman himself, Brandon Routh. Smith took care to wait until Routh had shot his scenes to inquire, “Hey, man, don’t you have some kind of morals clause?” But as long as Routh isn’t playing another superhero, he’s free to appear in a movie with “porno” in the title.

Smith had nothing but praise for Pittsburgh, where he and his family lived during the production.

“It’s a great town to shoot in. They were great to us on ‘Dogma,’ they were doubly great to us on ‘Zack and Miri.’ ” Anything anyone could do, they did.

His only complaint? The weather, admittedly outside everyone’s control. He could have used more real snow instead of having to make fake white stuff to hammer home the wintry setting.

As for what Pittsburgh lends to the movie, he said, “You look at Pittsburgh and, particularly, Monroeville, this is the last place in the world anyone would shoot themselves having sex, and that’s what I think was kind of ideal about the location. It’s the last place in the world you would think about somebody trying to kick off a porn industry.”

Add in the opportunity to film at Monroeville Mall, as George Romero did, and it’s a double win for a movie buff such as Smith.

The idea for this movie had been germinating since “Chasing Amy,” and Smith envisioned casting Ben Affleck, Jason Lee and Joey Adams in a picture about amateurs making porn. “But we never got around to doing it. We did ‘Dogma’ first and then life just took us in different directions.”

Smith never wanted to do a movie about the porn industry — Paul Thomas Anderson took care of that with “Boogie Nights” — but about “DIY” (do-it-yourself) porn. Zack and Miri, friends since first grade and roommates, are so cash-strapped that they decide to “make a porno.”

The fictional couple don’t have to contend with the MPAA, which initially slapped “Zack and Miri” with an NC-17 rating. Two scenes were especially problematic, and although Smith submitted a new cut, he couldn’t shake the strictly adult rating, which is when he asked to move to the appeals process.

Sounding more like a lawyer than a filmmaker, he said he was able to argue his case, offer a rebuttal and cite precedents that had pushed the envelope but slid under the R umbrella. His examples ranged from “Trainspotting,” “Jackass Number Two” and an “American Pie” sequel to “Taking Lives” with a steamy sex scene between Angelina Jolie and Ethan Hawke.

“That scene is meant to be erotic and titillating, ours is comedy. It’s a caricature of sex that’s already a caricature of sex because you’re lampooning porn sex.”

He won the ratings battle — the movie is rated R for strong crude sexual content including dialogue, graphic nudity and pervasive language — but lost the poster war. He eventually switched to one with stick figures and the message: “Seth Rogen & Elizabeth Banks made a movie so titillating that we can only show you this drawing.”

Still, Smith thinks this movie could take his grosses and blend of gross-out and sweet humor to new heights.

“We have a $30 million ceiling on pretty much everything we’ve ever done and we’ve never made more than 30 million bucks. For years, I always felt like there’s no way you could mix raunch with sentimentality and make more than $30 million, and then Judd [Apatow] proved that’s absolutely wrong.

“That’s great, he kind of opened it up and took that sensibility and that kind of movie we’ve been doing since ’94 into a mainstream arena. Not only did we get to borrow his guy, but we also get to live off some of the trailblazing.”

DVD rentals and sales, he says, are wonderful. “The only reason I continue to work is because our home video numbers have always been really, really strong. That’s where we apparently shine, but it would be nice to have one that shines just as well in theaters.”