The Algorithms Behind Moana’s Gorgeously Animated Ocean

In the early days, when motion pictures were still new, filming the ocean was a radical idea.

A surface-level shot of the waves was certainly feasible, but capturing footage of swaying undersea fauna, swimming fish, and marbled sunlight dancing on the seafloor? The consensus was: It couldn’t be done.

In fact, it could be. A century ago, the brothers John Ernest and George Williamson, the sons of a sea captain and inventor, would prove it. To do so, the Williamsons turned to a piece of technology their father had designed for divers in undersea repair and salvage jobs. The device was a series of flexible concentric tubes, “interlocking iron rings that stretched like an accordion,” as the Library of Congress puts it, made to suspend from a specially outfitted ship so that a diver could descend into a watertight chamber below. At one end of the tube was the boat on the surface of the water; at the other, the submersible room.

John Ernest and George were enchanted by their father’s machine. From the glass portals along the tube, they observed red snappers, yellowtails, fat groupers, and other shimmery creatures weaving through the coral reef of the Bahamas. And they had the idea of bringing a camera with them next time. Later, when they shared their still photos with newspapers—images included a blurry oblong shark and shadowy seaweed—it created a sensation.

Eventually, the Williamsons’ tubes—outfitted with a new, specialized spherical observation chamber that had a large funnel-shaped window—would be used to film the underwater scenes in the 1916 film, 20,000 Leagues Under the Sea. “I call this my magic window,” one of the silent film’s intertitle cards reads, before revealing a gray, clouded ocean view. “We gaze on scenes which you might think God never intended us to see.”

At the time, the footage was extraordinary. The film was a smashing success.

Filmmakers have been using technology to push the limits of how the ocean is portrayed ever since—and not just in live-action films. Most recently, Disney dazzled audiences with the animated film, Moana, which tells the story of a girl from the Pacific Islands who sets out on a voyage to rediscover her ancestors’ wayfinding heritage.

Moana’s directors, Ron Clements and John Musker, have been obsessed with stories about the ocean for decades. They made The Little Mermaid in 1989. The 1940 film Pinocchio, with its famous whale sequence, is what first inspired Clements to pursue a career in animation. But depictions of the ocean in those stories are nothing like what audiences see in Moana, which is as groundbreaking for its portrayal of water in 2017 as 20,000 Leagues Under the Sea was in 1916.

“Water is always hard,” said Marlon West, the co-head of effects animation for Moana. “Usually, in animation, we have a dozen water shots. They’re hard to do.” In Moana, however, the majority of the movie involves water. And the ocean isn’t just a presence; the action takes place on the water, introducing yet another layer of complexity. On top of that, Moana’s Pacific ocean is occasionally anthropomorphic, like a distant cousin to the water in James Cameron’s The Abyss.

Disney’s software team came up with a program it calls Splash—a companion to Matterhorn, which was used to create the snow in Frozen—to help automate the way the water would behave in various shots. Splash is a “fluid solver” that plugs into Houdini, third-party 3-D animation software. To use the solver, effects specialists would define the area they wanted to simulate—say, a section of water around an animated boat—then use a setting to determine what the ocean condition should be like to begin with. From there, they’d run the simulation on the pre-determined ocean surface, to animate how that area of water responds to the boat. The output from that simulation—“millions of particles,” essentially millions of new points of animation data—would then be smoothed into the final rendering of the film.

Splash also involved a series of algorithms that could simulate splashes, eddies, and wakes. The program’s buoyancy algorithm made it so the huge navigating canoes in the film bounced in and out of waves realistically. (In several shots, many of these canoes appeared in the water together, in close proximity, creating an additional animation challenge.)

“As effects artists, working with fluids, you can’t always predict what you’re going to get from your water simulation,” said Erin Ramos, the film’s effects lead. “And the hard thing with water is, if it doesn’t look right, you can really tell. Even if it’s in the background.”

Disney effects specialists told me they were able to successfully automate key ocean-movement details about 80 percent of the time—meaning you could have a production assistant simply run a script to generate the animated boat’s wake. “Running these scripts to generate these animations leaves room for the artists to focus on the artistry of the shot,” Ramos told me, “so they have time to create these sweeping shots, and the ability to have the ocean acting as a character.”

The ocean in Moana is an anthropomorphic force that occasionally nudges Moana along the way. Except the ocean character doesn’t have a face. And it doesn’t talk. (In this way, it was a bit like the animated magic carpet in Disney’s Aladdin, Osnat Shurer, the Moana producer told me.) So Disney’s effects specialists and animators were constantly navigating the tension between wanting the water to look and act like actual water—but to be magical at the same time.

“That was a big challenge,” West said. “They would animate the ocean as almost a sock puppet, and we would take that and fill it full of bubbles and liquid or we’d do a simulation over it and make it full of water to make it look more watery.”

There were many debates among animators and effects specialists over how to convert the ocean from its ordinary state into a character with agency and back again. “What made the ocean character look like water to one person, looked too agitated and aggressive to another,” West said. “You have the ocean often as a chartacter looming over toddler Moana and looming over Moana’s grandmother, and at no point do you ever want to be afraid for them. You want to be in awe.”

In the end, calibrating between those two expectations—a realistic-looking ocean that could also convey subtle warmth and encouragement as a character—meant keeping a portion of the water unnaturally smooth and rounded when it surfaced as a character. Also, there were moments when obeying the laws of physics were discarded in favor of keeping the audience focused on the characters. “Because it’s storytelling,” West told me. “It’s a stylized world. And we’re trying to create water that exists in your heart and your mind’s eye.”

Then there was the question of representing the ocean in an authentic way—not physically realistic, but culturally true. To do so, Disney formed an Oceanic Story Trust, a group of cultural practitioners from around the Pacific who acted as consultants on the film. Members of the trust weighed in on everything from haka chants to tattoo design to the demigod Maui’s hair. (He was drawn as bald at first. He shouldn’t have been, members of the trust said. Disney gave him luxurious hair.)

On their first research trip, to Fiji, the filmmakers met with Jiujiua “Angel” Bera, a skilled wayfinder. “He spoke about the ocean in such a personal way,” Osnat Shurer, the Moana producer told me. “He would stroke it really gently, and told us you had to speak gently to the ocean. ‘The ocean knows,’ he said. He goes out to greet the ocean in the morning like he greets his family. This left a very deep impression on us.”

Shurer and her colleagues were also struck by a larger theme of connectedness from the Pacific Islanders they met—and the way many island cultures see the land and sea as indistinct. (In ancient Hawaii, for instance, this idea was encapsulated in the concept of ahupuaʻa, divisions of land that run from the mountain down to the ocean.) And also the extent to which some cultures view the ocean itself as a connective force. “In the Pacific, we don’t consider the water a barrier to each other,” Dionne Fonoti, an anthropologist and a member of the Oceanic Story Trust said in an interview with Disney that’s in the Moana bonus features. “It’s not just the cultures of the people and the islands that connect us, it’s also the ocean that connects us.”

When the film project began, however, the Disney team had no idea how they could portray all this complexity—even just from a technological standpoint. Not to mention the separate but related challenge of animating an anthropomorphic volcanic island.

“I’m pretty pumped up about what we did,” West told me. “There’s nothing, when I look at the final film, that I cringe at. And there usually is.”

The project also changed the way that animators and effects specialists think about the actual ocean. Ramos, the effects lead, told me she spent more than a year and a half working on getting the shoreline animation just right. Even now, she says, she can’t go to the beach without noticing things she’d never considered before her work on Moana.

“You know it’s hard for me to go to the beach nowadays,” she said. “When I’m there, I’m looking at how foam dissipates, at how the water recedes back into the ocean, the cadence and the rhythm of the little breaks. I’m looking at how the beach itself is modeled to create the reef breaks, how the light affects the water, the clarity of the water itself, the colors. There’s just a million things going through my head.”

“I don’t think it’s a bad thing,” she added. “I think it’s gorgeous.”