The greatest challenge for the filmmakers was re-creating the titular martial arts with animated characters in a way that was unique to the characters.
"We didn’t want it to look like human beings wearing animal costumes. We had to imagine how each character would do kung fu, based on the physiognomy of the animal itself," Stevenson outlines.
Story artists Jan Nelson and Simon Wells conceptualized the action sequences with the help of Rodolphe Guenoden, a storyboard artist and martial arts practitioner who served as animation supervisor later on.
"He understands kung fu and how it works on the anatomy," says Stevenson, comparing him to Wu Ping, the martial arts choreographer who created the moves for "Crouching Tiger, Hidden Dragon."
Sketching out the fight sequences in 2-D first, "He was able to show people how a particular movement would go. It was a very interactive process and if we didn’t have Rudolf I don’t think we’d have been able to do it."
Black, whose favorite scene is an early one where Shifu teaches Po the basics of kung fu with chopsticks and dumplings, thinks they really brought the spirit of kung fu to the animation. As for Po’s unique approach to the martial arts, "Po’s style is soft and bouncy -- a heavy butt squisher," Black laughs. "If he sits on you, it’s pretty much over!"
As you’d expect, there’s a lot of comedy in the movie, but the directors were careful to ground their characters in reality. "We realized we had to ask the audience to buy into talking animals and ancient China, so the acting had to be very real. If the characters moved in a way that was too cartoon-y you wouldn’t understand the change up. So even though we had these cute animal characters we tried to make them act in a very real and genuine way when they weren’t doing kung fu," Stevenson explains.
Each character presented its own challenge. "The crane is individually feathered. The snake required a huge amount of technical R&D and innovation to make her fully rigged and capable," Stevenson points out. "Then we had furry characters, wearing clothing, which is very complicated interaction, and we had them doing kung fu. The rigs -- the things that make the characters move -- are much more complicated than the rigging in any other movie."
With the characters in the most realistic animated form possible, the directors then had to turn their attention to achieving a true representation of the landscape of ancient China.