• silicon.com
• Management
• CIO Insights

By Daniel Terdiman, 28 May 2009 17:06

NEWS

...because the simulator does indeed run with those conditions and rules and the peculiarities of physics, the animators found themselves without precise control of what would happen with the balloons - or other objects in the film animated using these techniques.

"If the [balloon cluster] is moving too slow, we increase the amount of wind, and then run the simulator again," May said. "Then maybe we turn the wind down. It's a little fun science experiment where sometimes, hopefully by the end, we're getting what we want."

Losing control of balloons Sometimes, given the vagaries of physics and chaos theory, unexpected things happen. The computer team inputs the rules and because some of the initial conditions are random, "you get semi-random results". One of May's favourite examples is that early in the film, when the house is first hoisted aloft by the balloons, a small group of the balloons actually broke off from the main cluster.

May said that this breakaway group of balloons is actually visible in Up. Eagle-eyed moviegoers can see the escaped balloons in the upper right-hand side of the screen, he said.

"We didn't mean for that to happen," he said, "but [we said] 'It's cool, let's keep it'."

Even being able to make such choices wasn't possible at the beginning of the film's production, however. May said Pixar's physical simulator, an open-source program called ODE, couldn't initially handle the complexity of modelling the behaviour of more than 10,000 balloons.

"We could handle about 500 [balloons], and we knew we needed tens of thousands," he said. "We knew we needed to develop a new simulator software pipeline...to handle an order of magnitude more complex simulation."

In Up , there were additional animation challenges. Among them were figuring out how to animate and render the feathers on Kevin, a bird that is a major character in the film, and how to make the cloth on the characters' clothes seem believable.

Carl Fredricksen's, the main character, threads were "the hardest clothing we've ever had to animate here", said May, "in part because Carl's a [small] man in an oversized suit. That was another case of using the physical simulation, and of setting up rules for how cloth should behave. And the looser the clothing, the more it can behave badly."

Still, for the award-winning filmmakers at Pixar, the goal is to make even the hardest animation problems look simple on the silver screen.

As producer Jonas Rivera put it, "The audience looks at [the balloon cluster] and says, 'Oh, that's pretty.' But they have no idea how much work went into it. We worked on that for over a year. [Then] the kid takes off his hat and runs his fingers through his hair. My mother will never know that took 15 people six weeks."