Issue: Volume: 24 Issue: 1 (January 2001)

Birds of a Feather

by Barbara Robertson

Of all the animated films shown during Siggraph's Electronic Theater, Pixar Animation Studio's "For the Birds" prompted the biggest reaction. The audience started laughing right from the beginning, when the first bluebird sitting on a telephone wire started grousing at the second fat little bluebird to fly in, and people kept laughing all the way to the last scene with all the newly naked little birds, wings crossed in front of them.

The latest in a series of short animations created with 3D graphics from Pixar, "For the Birds" was written, storyboarded, and directed by Ralph Eggleston, the art director for Toy Story, Pixar's first feature film, and produced by Karen Dufilho, head of development for Pixar Shorts and producer of Pixar's "Geri's Game."

"For the Birds" is already gathering awards, having received the Best Short Film award (audience vote) at the Catalonian International Film Festival (Sitges, Spain) in October; and an Annie from ASIFA-Hollywood (International Animated Film Society) in November for Outstanding Achievement in an Animated Short Subject. Pixar has submitted "For the Birds" for consideration by the Academy of Motion Pictures, and if nominated next month, the film will join a growing list of Pixar shorts to achieve Academy recognition: "Luxo, Jr." received a nomination in 1987; "Tin Toy" (1989) and "Geri's Game" (1998) both got Oscars. The film could have a good chance.
Pixar developed new tools to help squish the birds together without interpenetration. Changing the birds' eyelids and beaks helped animators give each one a personality.

In addition to festival awards, Internet Movie Database reviewers have given "For the Birds" a 9.5 rating out of 10, using phrases like, "leaves you rolling in the aisles" and words like "hilarious" to describe it. How does the studio keep rolling out winners? Talented people, good stories, and attention to detail in every aspect.

Although most films begin with a story idea, "For the Birds" had a different origin. "I came up with the idea as part of a design project back in the mid-'80s when I was a student at CalArts," explains Eggleston. "I had to work with shapes, so I started futzing around with a story about a big bird that lands on a wire and little birds that get squished together because they couldn't get away." That exercise with shapes evolved into a story that could be a metaphor for human behavior on the playground... or in the corporate world, for that matter. Or, the film could be viewed simply as good slapstick comedy.

It starts with the camera panning along wires between telephone poles, a wheat field below. A fat bluebird lands on the wire, ruffles his feathers, bends over and wiggles his tail. A second bluebird lands beside him and stretches. When his wing touches the first bird, that bird starts yammering in complaint. A third bird lands, a fourth, and soon there are 15 birds on the wire, all jostling and chattering to each other. The pandemonium builds until it's stopped suddenly by a loud squawk.
The design is cartoony, but the big bird waving to the little birds below has 3600 feathers and there's rust on the telephone pole's bolts.

The squawk comes from an odd-looking, long-necked big bird with a goofy grin that's sitting on top of the telephone pole. He wiggles his topknot of feathers and waves broadly to the birds on the wire. One of the fat little birds starts mocking the big, tall, skinny bird and soon all the little birds are ridiculing him. They begin whispering to each other and start moving away from him, but not soon enough: The big bird plops onto the wire in the middle of the line of little birds.

His weight causes the wire to stretch and the little birds on either side to slide down and become squished up against each other and him. One little bird pecks at the big bird, then another. The big bird jumps forward, but his toes curl around the wire, so he hangs upside down, still grinning. The birds close to him start pecking his toes...with encouragement from the rest of the flock: Their squeaks now sound like the chants of a mob.

With one toe left hanging on, the camera pulls back to show the wire now stretched tautly into a deep V with the big bird's upside down head only an inch from the ground. One little bird gets a stricken look on his face and tries to stop the pecking, but it's too late. Big bird's toe lifts off the wire, the stretched wire snaps, the birds shoot into the air and we see a pattern of blue feathers where the little blue birds once were. The camera takes us to the ground. The big bird sits up, and one featherless pink bird with a blue feather sticking up on his head drops from the sky to land next to him. Big bird hands the little bird a leaf. The little bird takes it and holds it in front of his naked body. Then, the rest of the naked little birds fall to the ground, cross their wings in front of themselves, turn, and waddle away as big bird gets the last laugh.

Eggleston describes the big bird, nicknamed "Leo," as "a big, dumb bird that just wants to have fun. Even when they torture him, Leo doesn't quite get it," he says. For reference, the animators looked at flamingos...and Stan Laurel.

"If you watch Laurel and Hardy, Stan Laurel was the one with the 2 by 4 who'd turn around, causing it to smack Oliver on the face and then ask, "Oh, what are you doing on the ground?" explains James Ford Murphy, supervising animator. "That's what I wanted Leo to be. Dense, but charming."
The first four birds to land on the wire have distinct personalities: Chipper, Bully, Snob, Neurotic. The inset shows the little birds mocking the big bird.

As for the 15 little birds, "All the birds are the exact same model, and they're really doing the same thing-landing, bumping into each other, pecking, arguing, doing their shtick," Murphy says. Murphy did the blocking for the little birds' choreography using a sound track made with squeaky toys. "Each squeak sounded like an inhale or an exhale," he says. "As an animator, that's what you're looking for. If the squeak sounds like it's going up, you make the animation go up for one bird and it looks like it's connecting with that bird."

Murphy gave the first four birds that land on the wire distinct personalities: The first one plays the part of a bully throughout the film-he's first to mock the big bird, he pecks the big bird first...and he's the first bird to land naked at the end. The second bird, "Chipper," is a happy-go-lucky, lazy, little guy; the third is a snob; and the fourth bird is neurotic and nervous. The animators used these four as a jumping off point for animating the rest of the flock. They didn't duplicate them; the first birds simply started the ball rolling.

"Individually, the birds had their own personalities, but as a whole, there had to be a real sense of rhythm in the shot," Murphy says. "Once they were all in the shot, they became like a big caterpillar; each section [each bird] had his little business that affected the other sections so that when you look at them all together you're not concentrating on an individual, you're concentrating on the whole. I found it was a big lesson in contrast-making one bird's pose stronger by contrasting it with another. A second big lesson was in choreographing where we wanted the audience's eyes to be."

All told, 15 animators worked on the film's 50 shots. Murphy animated the complicated opening sequence and Ben Catmull, a student assigned to the project for the summer, animated between eight and 10 shots. Animators doing one or two shots when they could take time away from other Pixar projects handled the rest. The animators, who were assigned shots rather than characters, created several layers of animation for each: the acting poses for the birds, facial animation, secondary animation, the contact between birds, the feathers, and the wire.

Animators at Pixar work with proprietary software called MenV; characters and scenes are modeled with Alias| Wavefront's Maya and with Pixar's own modeling tools. Although the story evolved from Eggleston's original design project, the character design for the little round birds remained the same. "Because we try to have a strong underlying structure for our characters, I started changing the design, but John [Lasseter] wanted the original design," says Eggleston. "So we put a bird's skeleton inside a ball. It looks like a cartoon on the outside, but everything inside makes it work as a real bird would work, save the edges of the mouth."
Two little birds, one imitating the big bird, are shown as models (left), with feathers (middle), and in a final rendering (at right). Also shown is the wire, which was animated at the end, after all the birds were in place.

The animators had to take these balls and turn them into fat birds. "When we first started testing the little guys, I did a walk test and they felt like hard eggs," says Murphy. "When they walked, there was no follow-through and there really isn't much to follow through with, so we put in big belly jiggles."

The biggest technical challenges for the animators, though, were in making the contacts between the birds work and in animating the feathers, and these required new tools. "A great deal of the film was predicated on the fact that we could make these little birds look like they were all stuck together," says Murphy. "It's a big challenge in computer animation to make things look like they touch but not intersect. Also, if two birds are stuck together and one moves, the other one has to go a little bit with the first one."

"The first time I looked at the storyboards, the bird-to-bird interaction seemed like it would be the biggest technical issue," says Bill Wise, supervising technical director. "Nothing gives that computer graphics feel more than objects that pass right through each other." The birds offered a special challenge because they needed to squash tightly up against each other without interpenetrating . . .or at least appearing not to interpenetrate. "It was a story point that you really needed to feel the pressure," Wise says. He initially considered creating simulation software to preserve the birds' volumes but decided against it for budget reasons and because he wasn't sure a simulation would give animators enough control.

Instead, he created bendable, disc-shaped collision detection widgets that he called "contact pads" and Eggleston called Pringles, after the potato chip, because of the shapes they took. (The pads would, of course, ultimately be invisible). Wise placed the contact pads between birds and created hooks to the birds; the animators shaped the pads and animated them. "There was code in the birds to evaluate where they were relative to the contact pads," explains Wise.
All the little birds have the same simple shape, but inside each is a real bird's skeleton. Here, the featherless birds use their wings and one leaf to preserve their modesty after the fall.

The code in the bird checked to see if any of the bird's points were in a bounding box defined by the contact pad. If a point was outside the box, the point stayed in the same place on the bird; if the point was inside the bounding box, it moved, and that changed the bird's shape. In other words, as a bird with hooks to a pad got close to that pad, the pad triggered articulation of the bird's body into a shape determined by the shape of the pad.

"The nice thing is that if you have two birds side by side and one contact pad between them, they can both squish up against it," Wise says. "And when a bird's surface distorts, the feathers go with him, which is what you'd want. The only downsides are that it takes time to project points, and the animators had to do this animation as a second pass." That is, the animators would complete all the acting for the birds, and then add the contact animation. Once that was done, they'd work on the feathers.

"The feather pass was the very, very, very last thing we'd do," says Murphy. "Feathers were a pain because they were so heavy, but they were so effective. They really just added that element of 'birdieness.'"

To help the animators work with feathers, Wise created smaller versions of the feathers for the animators to use and devised methods for animating fewer feathers. In addition, he optimized the software. Each bird had 2873 feathers, which contributed to an early memory footprint of 400mb. Ultimately, however, Wise was able to reduce the memory requirements to 45mb.

In addition to the main feathers, geometry was added to each bird to soften its silhouette. "Ralph wanted certain areas of the feathers to be down y and fuzzy, and for the edges to be hairy and not like hard shingles," Wise says. To create this look, the team used little spheres mapped with hair and transparency textures.

Wise also added feathers to fix bald spots. When an animator moves a bird's brows into a cartoony frown, for example, the surface stretches and that causes the feathers to spread apart. "There's one shot where two birds looking at each other fill the entire screen. In that shot, the bald spot would have been half as big as me, so I had to do something about it," says Wise. To patch the bald spot, Wise wrote software that would create copies of particular feathers and distribute them semi-randomly around the original.

To help with feather animation, Keith Gordon, who has since left Pixar, created macro controls that Wise later refined. "The feathers weren't new technically, but the controls that allowed animators to animate individual feathers or groups of feathers were something we hadn't tackled before," says Eggleston. The macro controls could move all the feathers up or down in sections-top, midtop, mid, and lower-and the sections could overlap. "You could puff the feathers and you could shuffle them," says Murphy. "There was even a little random shuffle macro that was great."

To animate the feathers left in the air when the wire snaps, Wise used Pixar's particle system. "We captured the transformation matrices for each feather on the birds' bodies at that point, then fed the data into our particle system. After that, it was pretty straightforward. We'd tweak gravity, wind, spin, and mass until we got the effect we liked. A lot of that tricky tweaking was done by Keith Gordon."

The team also used procedural modeling to create the wheat, using code that Wise wrote. The program starts with a central stalk, adds a specified number of leaves and a tassel, and uses parameters as input for length of the stalk, and length and width of the leaves. "I generated a noise field based on the 3D location and bent and rotated and scaled all the various parameters to create the field. That was interesting, but the tricky thing was the lighting effect Ralph wanted," he says.

Similarly, the lighting of the birds' feathers was tricky. "Ralph wanted the feathers to look soft, yet shine at the proper angles," says Jesse Hollander, who worked on lighting for the film. "He wanted a hot, sunny day and he wanted the audience to feel the heat."

"These characters are very cartoony, yet they exist in a kind of Pixar realistic world," Wise adds. "This film is more stylized than before, but there is still complexity and realism. I think the birds are our most cartoony characters."

"At Pixar sometimes short films are designed to test new technology," says Eggleston, noting that in "Geri's Game," the cloth simulation program was tested. "This film was more for fun."

Barbara Robertson is Senior Editor, West Coast for Computer Graphics World.