At age 17, Paul Thomas Anderson wrote the first version of Boogie Nights (New Line Cinema). In the next 10 years, two hours were added to the half-hour original.

Inspired by his childhood in the San Fernando Valley, the capital of porn-making, Anderson said he always has wanted to write the backstage story of the industry.

“It always sort of surrounded me in a peripheral way. I had a sort of fascination with pornography. On a filmmaking level, as a genre, I was always hoping and wishing that it was better,” Anderson said.

He added that he wanted to convey the sad and depressing element of the business as well as the excitement.

Anderson said he did not do research before writing the screenplay. “Going to the sets (afterwards) was only to verify,” Anderson said. “It was even funnier than I thought it was going to be, and it was even sadder than I thought it was going to be.”

Though the industry’s switch from film to videotape was a part of Anderson’s film, it was not a major focus. In the change, Anderson said, the genre lost all links to legitimate filmmaking.

He used lenses from the 1970s to add to the feel of the era created by the setting, clothing and dialogue. He said during the filming he had to pare back on some of the clothing as to avoid being dubbed “camp,” though it was authentic.

Anderson said he has been questioned from older critics who wonder how he could have gotten the era so right.

“Well, maybe I was young and sober, and you were stoned, and you don’t remember it. And maybe, it’s not even right,” Anderson said.

Anderson said he had to be careful with costumes and music because so many people distinctly remember the 1970s. “We had to have the songs to the month,” Anderson said “Because I don’t want anyone calling us out on it.”

“There is one cheat in the movie, but I won’t tell anyone what it is,” Anderson challenged.

Hope “glimmered” in the 1970s that the porn industry could take a turn for the better, Anderson said.

Anderson compared the character of his creation, Dirk Diggler, to 1970s pornographic filmmaker John Holmes. He said those porn films were wonderfully structured around solving a mystery, but leading men had to have sex beautiful women to get crucial information.

“Seventies pornographic filmmaker John Holmes started out as a suave, smooth guy, but as drugs and ego took their hold on him, his characters totally changed. Instead of charming the clues out of (the women), they were beating it out of them,” Anderson said. “You watch this guy and wonder `where did it all go wrong?’

“Dirk starts out caring about his dick and his car and his antique furniture,” Anderson said, pointing out the parallel between Holmes and Dirk. Dirk also took a deep dive after getting into cocaine.

Anderson said he tailor-made many of the roles for his actor-friends, but Mark Wahlberg was not his first choice for Dirk. He said he originally wanted Leonardo DiCaprio, but is happy Wahlberg ended up with the part.

“Not because Leonardo would not have been good, but because Mark is phenomenal. It would have been a different thing,” Anderson said.

Anderson confirmed the rumor that when Wahlberg said he wanted the part of Dirk, he proclaimed he was an inch longer than DiCaprio.

“Leonardo showed his penis, and Mark showed me his, and I said `Mark, you’re in,’ ” Anderson joked.

Really no choice was to be made. DiCaprio had decided to take a part in The Titanic, Anderson said.

Looking back on the negotiations with the rating board, Anderson said the struggle to keep the film R-rated was not as difficult as it seemed. He said he did not have to lose any essential scenes.

And about the last scene, when Dirk pulls out his penis, Anderson said the board “never said one word. But what could they say? They knew they would have been accused of a double standard.”

“I wrote it really selfishly,” Anderson said, without any specific audience in mind.