Piece By Piece, the new documentary about musician Pharrell Williams, is unusual in many ways – not least because it’s animated entirely with Lego.

Critics hailed the film’s unique visual style, calling it “disarmingly cheerful” and “strangely charming” – but they also questioned one of the film’s great omissions.

Robin Thicke’s Blurred Lines, which Williams co-wrote, is briefly heard on the soundtrack, making no reference to the song’s infamous plagiarism lawsuit that left the musician owes $5 million to Marvin Gaye’s estate.

Speaking to the BBC, director Morgan Neville said he wanted to address the controversy, but the sequence ultimately derailed the story he was trying to tell.

“I definitely thought about it. I even interviewed Robin Thicke,” he said. “And as a documentary filmmaker, I’m obsessed with copyright law.

“But every time I watched him try to work in a scene about copyright law, it felt like it belonged in another movie.”

The Blurred Lines trial was hugely important to the music industry after a jury ruled that Williams and Thicke had copied the sound and “feel” of Marvin Gaye’s Got To Give It Up – rather than plagiarizing a specific song.

The general consensus among music lawyers and songwriters is that the verdict failed to distinguish between influence and theft.

It has now become common practice for musicians to attribute a portion of their royalties to songs that directly inspired them.

“My view on the Blurred Lines case is that it’s one of the worst judicial decisions about creativity in history,” Neville told the BBC. “I think Pharrell was right and I think most creators agree with him.”

Ultimately, this led him to leave the story out of the documentary.

“It’s not like Pharrell learned a big lesson from this case. I don’t know if it really changed him in any way, which is what I look for when I look at a story.”

Williams has been contacted for comment.

Neville previously won an Oscar for 20 Feet From Stardom – a documentary about the forgotten lives of the singers featured in some of rock’s biggest songs.

Other subjects of his documentaries include Keith Richards, Brian Wilson, Johnny Cash and, as a producer, Taylor Swift.

With Piece By Piece hitting theaters this month, Neville told us about the film’s unexpected genesis, how he got Lego on board, and the stars who had notes about their Lego minifigures.

In the movie, you dramatize the moment when Pharrell asked you to make the movie in Lego, and your response is, “Lego? Serious?” How true was that to life?

The main difference is when Pharrell said “Lego movie” I thought “Hell yeah!”

I knew it was a crazy idea, but an exciting one. I think it took me five minutes to fully buy it.

Can you break it down for me? What was Pharrell’s argument?

He basically said, “People have always wanted me to tell my story and I’ve never been that interested, but I love your movies and I had this idea that you could make a documentary about me and when you’re done with images and make it like Lego again.”

That’s pretty much exactly what he told me – but beyond that he had no idea what it meant or what his story was. So I got to thinking, what does that mean?

And one thing I realized right away is that it’s not just about taking real-life documentary footage and making Legos out of it. It uses what animation can do, which is time travel and going into outer space and all kinds of things that you can’t normally do in a documentary.

How quickly did it go from crazy idea to reality?

It took us about a year from when we first met to start production because we had to meet with Lego and tell them about it.

How did the conversation with Lego go?

I said, “Look, it’s not a G-rated movie, but I understand it can’t be R-rated either. It’s something that has to have a little edge, and it’s going to get into issues of race and stuff.”

And Lego, to their full credit, said, “These are conversations that are good to have.”

They knew he would push them, but in ways they thought were good.

But they didn’t fund it, they don’t own it, they’re just partners.

What was the moment you knew it was going to work?

Well, we had to figure out how to get someone to pay for it, so we did a 90-second proof of concept.

I interviewed Pharrell and cut a scene of him listening to Stevie Wonder as a boy on his parents’ stereo – and his synaesthesia begins. Suddenly there’s a lot of color and you can almost see what’s going on in his mind. That convinced me it would work.

I love how you visualize Pharrell’s beats as Lego sculptures, each with its own unique shape. It really helps illustrate the abstract concept of songwriting.

You know what was interesting about the beats? Pharrell, in his mind, can tell you the color and shape of every beat he’s made. So for each of those Lego pieces, we worked with Pharrell to make sure they looked like what he saw in his head.

When you were interviewing other people for the film—Missy Elliot, Jay-Z, Snoop Dogg—did you tell them it was going to be in Lego?

We didn’t, partly because we filmed those interviews five years ago and wanted to keep it low-key.

Then, cut to a few years later, and I started sending 3D renderings of their characters, like, “Look at her. This is how you will look.”

It was a bit of a roll of the dice, but everyone was really excited about it.

Has anyone requested changes?

Missy had a comment about her earrings, so one of the few custom (Lego) pieces we made for the movie were Missy’s earrings.

Lego characters have a limited range of facial expressions. Did that pose a problem?

The face thing was the most worried, because when you have close-up shots of a Lego minifig crying, is it going to be emotional? I don’t know.

But there were a few animators on our team who were really good at facial animation, and we gave them the most emotional scenes, the close-up scenes. And often, if something was wrong, I would send them videos.

Somewhere in the world there are tons of clips of me and Pharrell making really weird faces!

The arc of the film is Pharrell rediscovering his muse after a period of creative loss. Why did you focus on that aspect of his story?

Without a doubt, the film reflects a lot of questions I’ve had about my own career.

For me, the story of this black nerd in the Virginia projects who sees the world differently… and makes him an outcast for a long time. Then he finds a fellow outcast in Chad Hugo (Williams’ co-writer in The Neptunes) and they start making music.

But their beats were too strange for humans. The Neptunes sound was very unorthodox. Nobody got it until everyone I understood. Then you end up in this hall of mirrors – where the thing that makes you different becomes the sound of the mainstream. When that happens, how do you stay true to yourself?

Your film comes out at the same time as the Robbie Williams biopic Better Man, in which he is played by a CGI monkey. Do you think musical biopics have become too formulaic?

Yes. There are so many musical movie tropes and I think we need to do more to help people identify with the people and their characters.

I haven’t seen Better Man yet, but the idea is perfect because, in a way, Robbie Williams it is the performing monkey. He wants attention. He always lived that life.

And Pharrell is the Wizard of Oz. He says, “I want to be the guy behind the curtain.”