Computer animation evolves at an alarming rate. One year, a movie like Frozen or Big Hero 6 looks like the peak of what’s possible. Then, only a year later, the next thing goes way beyond that. In this case, the next thing is Zootopia, and in this movie a single giraffe has more individual hairs on it—nine million—than every single character in either Frozen, Big Hero 6, or Wreck-It Ralph.

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Keep in mind that the filmmakers had to manipulate each individual hair on its own—and there would have been a lot of hair even if they hadn’t gone to such lengths. The film is, after all, about animals who walk, talk and dress like humans. Animals mean fur, and that’s something Disney Animation hadn’t done for a lead character since 2008’s Bolt. And even that was just a single character. So to make an entire movie full of furry animals, they had to create a whole new language in the computer to make it possible.

“When Snow White was released, it really was a technical achievement,” said Zootopia producer Clark Spencer. “And it really is our goal, as a studio, each and every day, to push technology and innovation. Zootopia follows in the footsteps of Tangled, Wreck-It Ralph, Frozen, and we’re competitive. Each of us look at our films and say ‘How do we go to that next level?’ And that’s really been an extraordinary journey for all of us in bringing this world to life.”

The lobby of the Tujuna campus of Walt Disney Animation, where Zootopia filmmakers had to develop new technology to get the movie made.

When Disney released Snow White and the Seven Dwarves in 1937, going to the next level in animation was different. The animation was done by hand and advances in technology were physical. These days, all of Disney Feature Animation is computer animated, so they have in-house engineers, developers and more, who build software that makes the stories the filmmakers imagine possible. However, with each and every film, the filmmakers push what computer animation can do, and that means creating tools that didn’t exist before.

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After doing tons of research on real animals both in nature, and in museums, the team came to realized that almost every single type of fur is different. They have different sizes, textures, densities and colors—and with each of those kinds, light passes through them in a different way.

Zootopia has 64 different species of animals, that break down into about 800,000 different character models. To get the right level of realism, hair has to be treated as multiple pieces, and not one cohesive thing. Which is nothing new. Elsa’s hair in Frozen had about 400,000 strands. But Zootopia pushes that further. A mouse in Zootopia has 480,000 hairs, while a giraffe has about 9 million. That means crazy computing power is needed, to animate and render each individual frame—and some took up to 100 hours to do, once they were fully realized.

In Zootopia, animals of all size live together.

Obviously, an animator can’t go in and move 9 million hairs individually though. So the team created a specialized fur shader, a tool in the animation program which could brush the individual hairs all together, almost like a comb, after being applied to each design. And that looks great, but only if the light is hitting each hair individually like it would in real life. To accomplish that, there’s a process called path tracing that predicts how light would move through the space depending on where it’s originating, and then it bounces off the hairs and exits. Because of these techniques, the otters look oily, sheep look fluffy and bunnies look cuddly. There are times when you watch the film, especially in close up, the characters look so real, you almost feel like you can touch them. In fact, path tracing the fur of one character in Zootopia with the new fur shader is as complex as lighting an entire environment was in one of the previous movies.

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That kind of realism also has a lot to do with ambient movement. When an animal is running, obviously air is moving in a very specific direction. But if the character is just standing there, there’s movement too, it’s just much more subtle. For Zootopia, software called xGen was given a whole new set of tools that built in an ambient, natural movement into the scenes. It worked on hair, as well as the environments, so that everything in the film that can move, is always moving.

Animals are more than just hair though, right? They’re muscle too. So that’s another layer that has to be considered when creating characters. A program named PhysGrid was created, that would add realistic muscle and fat movements below the skin of each character. It gives them all a good weight and shape, and allows animators to work as closely as possible to what the final image will look like.

The first part of the process. Storyboards.
Step two, the layout phase, where the camera and early animation come together.
Step three, final animation. Here the real emotion and dialogue are being put in.
Step four, the final shot. Notice how the lighting, hair, muscles and everything have been applied to create a much more realistic image.

That’s another key. Ideally, all of this—hair, movement, muscle—has to look as close to final animation as possible, when animating. You don’t want to be animating at one level of quality, and then have it look totally different on screen.

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That’s where a real time display engine called Nitro comes in. Inspired by the video game industry, it’s a software Disney developed to help balance the different between what an early animation looks like and what a final shot looks like. The problem is, Nitro had been around for so long that it wasn’t working well enough to handle the complex, realistic characters of Zootopia. So they had to keep upgrading and reconfiguring the software during production.

Plus none all this matters if the animals are walking around environments that aren’t equally as impressive. Enter a software, designed by Disney for this film, called Bonsai, which made the creation of various different kinds of vegetation simple, but also highly customizable and repetitive, to populate the various section of Zootopia very quickly. In fact, the engineers pushed the rendering system to its limits, and were able to do 7.7 million trees, which is over 4 trillion polygons, all at once, in a single shot. There are never that many at one time in the film, but that’s how far the software could go.

Judy Hopps and Nick Wilde take a cable car across Zootopia.

The scary thing is, you won’t see any of this in the movie. When you actually watch Zootopia, you concentrate on the characters and the story, and you probably never think about the people who for the past five or so years have been creating technology that’ll make light in a computer reflect correctly off 9 million strands of giraffe hair. You just see the giraffe. That’s the magic of filmmaking. Thousands of people working on a literally microscopic level, so that we can enjoy a brand new story without thinking about anything else.

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*Correction: After publication, two minor tweaks were made to this piece to clarify software usage and origins.


Contact the author at germain@io9.com.