Image courtesy of The Walt Disney Company

Taking Big City Greens from 2D to 3D animation in Unreal Engine

When Disney Television Animation wanted a fresh take on their holiday-themed installment of Big City Greens, they settled on a reality-bending premise that sees the Greens enter the virtual world of “Outpost Infinity,” a three-dimensional departure from their usual 2D style.

Translating well-known 2D IP into a 3D environment is easier said than done, however. By working with Disney Technology teams and utilizing Unreal Engine, they developed a look that stayed true to the original artwork, building out a real-time CG pipeline quite unlike the conventional 3D approach. Ultimately what the team had to do was take a 2D pipeline and flip the script.

At 16 minutes in length, highly stylized, and created almost entirely in engine, the 3D footage in ‘Virtually Christmas’ is the first Unreal Engine episodic work produced by Disney—and the longest single animated episode they’ve created primarily using real-time technology.

The Big City Greens holiday special finds the Greens facing a dilemma when Cricket Green is trapped in a snowstorm and unable to make it back to the family home for Christmas.

Fortunately, Cricket’s friend Remy has a solution—the family can celebrate together in the 3D environment of Remy’s new virtual reality game. “This gave us the opportunity to blend traditional 2D storytelling with 3D real-time storytelling, which is a journey that the characters themselves go on as they find their way into a virtual world,” explains Kaki Navarre, Vice President, Software Engineering in Technology at Disney.

Bringing animation from 2D to 3D poses a number of challenges—both from an artistic and a technical standpoint. Firstly, the 3D versions of characters must stay true to their original 2D counterparts.

“We wanted to make sure that the Greens felt like themselves—so that motion-wise and design-wise, when you look at it, you’re like, ‘oh, that's Cricket,’ ” says Jennifer Burchfield, 3D Animation Supervisor at Disney.

The project had been set up with a real-time pipeline based on Unreal Engine, but the art style of the episode demanded a different approach to a physically based game engine look—one that was highly stylized rather than photoreal.

Inspired by stop-motion and illustrative styles, the team developed a custom look that began to coalesce around a number of art and animation techniques. This necessitated the creation of a style guide for consistency that would define everything from how light and shadow interact with characters to how reflective surfaces should be.
Image courtesy of The Walt Disney Company
The team also looked to 2D animation to identify techniques they could utilize to bridge the gap between the 2D and 3D styles. “Big City Greens is a cartoon,” says Mark Droste, Director 3D Animation at Disney. “The characters’ arms stretch super far, their eyes get big and wide, their bodies can do things we can’t. Often, the concern with going to CG is that things become rigid—especially from a 2D perspective.”

To ensure the characters felt as cartoony in 3D as they do in 2D, the team knew there was one animation principle in particular it had to push: squash and stretch.

Squash and stretch is a technique 2D animators use to convey elasticity and flexibility. In characters, it makes the way they move appear more natural and alive. “If you pause on a frame, you’ll see some wild squashing and stretching, faces pulling to the side,” says Droste. “That really adds to the snappiness of the animation and keeps it feeling grounded in that Big City Greens style.”
Image courtesy of The Walt Disney Company

The team also started leaning heavily into geometry smears. Smear frames are a 2D animation technique where a moving object will be followed by several images behind it—almost like a smear. It’s a technique to give the illusion of continuous movement. “That got us more in line with Peanuts or Spider-Man: Into the Spider-Verse, that sort of approach,” says Burchfield. “We did the whole thing without motion blur—so the show feels more stylized.”

Achieving these techniques starts with the character rigs. The team authored rigs in Maya, then brought them into the engine for a previs animation pass using Control Rig.

The data was then baked out to an animation sequence and exported in FBX for the animators to do final passes in Maya. “We really wanted to push that squash and stretch look—and we didn’t want to do any editing outside of the engine,” says Evan Binder, Pipeline Supervisor, 3D Animation at Disney.

“For performance reasons, we decided to stick with FBX—primarily because we knew it was going to work well with Control Rig, and because we were going to be able to expose those controls to our artists to modify later in engine.”

With the final Maya passes done, the whole thing was brought back into the engine so the team could see it in its full context, add smear frames in engine, and make any changes. “You throw it back into the engine and you have it there in your set,” says Droste. “You’re looking at it with lighting, you can see everything the way it’s going to look in the final. You just keep iterating—and that cycle is so fast, you’re able to make decisions very quickly.”
Image courtesy of The Walt Disney Company

From Unreal Fellowship to first project

Disney has been working with real-time workflows for some time. Last summer, several team members took part in the Unreal Fellowship program. ‘Virtually Christmas’ is the team’s first project in Unreal Engine. “I really learned to love Unreal,” says Burchfield. “I had never opened it before and it was super easy to pick up. I found it very intuitive. I just felt at home in it.”

Opting for a real-time approach afforded the opportunity to parallelize disciplines that would have needed to be done sequentially in a traditional offline production pipeline. With editorial, layout, lighting, and VFX all running at the same time, teams had the opportunity to find the story in an iterative way, working in conjunction with one another in a consolidated environment.

For Megan Stifter, CG Supervisor, 3D Animation at Disney, this is one of the most powerful aspects of the real-time workflow. “In traditional animation, artists and engineers become used to working in abstraction,” she says.
Image courtesy of The Walt Disney Company
“You’re not working in the final context of how your work is going to be seen, so there’s a lot of guessing and checking—a lot of making changes that might take days, weeks, or months to see the ripple effect. When you’re working in real time, that’s completely shortened. You’re able to see your impact almost instantaneously.”

More often than not, that feeling was met with excitement. When siloed departments can start working together simultaneously, updating becomes an invigorating experience. Typically, that process started with cubes, cylinders, and previs assets created by the cinematic directors—all of which could now be worked on during layout, while the final assets were in production. The team could then use Blueprints, sub-level nesting, landscape sculpting, and stand-in props to keep production moving for the Animation, Cinematics, Lighting, and Tech divisions. Once the models were final, they could swap or update them easily in engine.

“Every day was like a new present to our eyes every time we synced all the files in Perforce and pressed play on the reopened project in Sequencer,” says Christina Douk, 3D Asset Supervisor at Disney. “It made iterating in engine so much fun and interesting, and kept the production feeling inspired as we moved forward.”

Real-time 3D filmmaking tools

Unreal Engine’s filmmaking tools replicate the tools you’d find on a physical set. Early on in the project, Droste went into the engine and roughed out the story by himself. “It was great—I was able to take this digital sandbox to go from my head to building this thing in engine,” he says.
Image courtesy of The Walt Disney Company
“I remember one of the best days was after we got the whole thing set up, all with previs assets. And it went from an idea to something there on screen. That’s my favorite part about using Unreal—just how easy it is to build out environments, throw lights in, set up your characters, and all of a sudden, your idea becomes something concrete in front of you.”

Every sequence in ‘Virtually Christmas’ was edited together in one overarching timeline using Sequencer. By bringing the editorial process into Unreal Engine, the team was able to work faster, view the entire episode and each shot in context, and make changes on the fly—removing the time-consuming process of exporting and syncing shots to traditional non-linear editing software packages.
Image courtesy of The Walt Disney Company

“It’s all one giant project that we can fly around in and do quick fixes that you wouldn’t be able to do in a traditional pipeline; a centralized content creation suite like Unreal makes this possible,” explains Andy Wood, Director of Technology, Real-Time Media at Disney.

The ability to adjust shots last minute paid dividends, particularly when a significant change was requested towards the end of production. “We wanted to redo a pretty lengthy sequence—that would ordinarily be a showstopper,” says Droste. “I was able to sit with the showrunner and redo the entire three-minute sequence in about two hours in Unreal Engine.”

A multi-platform content pipeline

Disney has always pushed the limits when it comes to animation technology, and its Technology teams have often pushed into new frontiers of real-time visualization. So going real-time for ‘Virtually Christmas’ just felt like a natural progression. “As technology advances, you wonder, how can we get more context faster? How can we work in new innovative ways?” says Wood. “It just made sense to explore real-time as a possibility for this kind of project.”

Disney’s use of real-time technology on ‘Virtually Christmas’ is part of a much larger picture. The company’s Technology and creative teams have been exploring the use of real-time workflows in other areas such as virtual production, content interactivity, data visualization, and more. With departments creating real-time content in tandem, an intriguing possibility opens up: the opportunity to create a multi-platform content pipeline.
Image courtesy of The Walt Disney Company
If the appropriate optimization decisions are made at the start of a project, CG assets and environments created for one vertical can be repurposed for use in another. “You make an investment in real-time-capable assets up front, that can run at interactive frame rates, and then you can use them for traditional linear flat content creation, or to produce any type of new format, whether that’s an interactive experience or something more immersive,” says Navarre. “The sky’s the limit.”

Big City Greens ‘Virtually Christmas’ is now available on Disney Channel and Disney Plus.

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