The Shape of Animation
Issue: Volume: 32 Issue: 6 (June 2009)

The Shape of Animation

Read in-depth features about how cutting-edge CG was created for various movies making Oscar buzz.

Pixar Animation Studios once again redefines CG animated features with its 10th film, Disney/Pixar's Up.

A square. A circle. Two fundamental shapes in geometry, two iconic shapes in computer graphics. And, the simple basis for the visual style—the shape language—of Disney/Pixar’s 10th animated feature, Up, one of the most sophisticated ever in terms of story, design, and technology. Directed by Pete Docter (Monsters, Inc.), co-directed by Bob Peterson, and written by Docter and Peterson, Up is an action-adventure, a comedy, a most unusual buddy film, a circle-of-life story, and Pixar’s first film in stereo 3D.

The personalities of Dug, Russell, and Carl show on their animated faces as they hang onto Carl’s balloonpowered house, while Kevin the bird catches an unruffled ride on the roof.

Carl Fredricksen, 78 years old and voiced by Ed Asner, is the square and the film’s central character. His default expression is a scowl. But, that’s now. When the story begins, he’s eight years old and enchanted by the exploits of the pilot Charles Muntz, who he sees in a black-and-white newsreel claiming to have found a prehistoric bird, a “missing link,” in Paradise Falls, South America. On his way home from the movies, little Carl meets Ellie, a bouncy tomboy, who is also a fan of Muntz and his motto, “Adventure is out there.” Ellie is Carl’s first circle. They marry, and we watch their lives spool forward. Carl becomes a balloon salesman. They save money for an adventure “out there,” but something always stops them—a flat tire, a house repair, medical bills. Even so, they’re happy as they grow old; life is colorful. And then, Ellie dies. The color fades from Carl’s life. He stays in his house and talks to Ellie’s picture. He becomes rigid.

But, two events happen. First, Russell, an eight-year-old Wilderness Explorer, shows up on Carl’s doorstep, much to the grouchy old man’s annoyance. Russell is a round little boy, full of joyful enthusiasm. He needs to help an elderly person to earn his last badge. Second, Carl finds himself sentenced to life in a retirement home. That spurs him to fulfill his promise to Ellie. As the retirement home orderlies wait at the curb for Carl to emerge from his house, 10,000 balloons rise up from behind the house and lift it from its foundations. Carl is on his way. He sits back, content, in his easy chair as his house floats past skyscrapers. And then, Russell knocks on the door.

 “When Pete and Bob pitched the story, with Bob reading, it brought John to tears,” says Jonas Rivera, producer, referring to the directors Docter and Peterson, and to John Lasseter, Pixar’s chief creative officer.
The idea originated with Docter and Peterson noodling around with an escape fantasy, of just floating away. They wanted to find a unique character, one they hadn’t seen before in an animated feature. Docter drew a grouchy old man holding a bunch of brightly colored balloons. They laughed, the brainstorming began, and soon the balloons were floating the old man in his house.

All they needed to do then was discover why the old man was in a floating house, where he would go, and what would happen when he got there. It took three years or so—Peterson, Docter, and story artist Ronnie del Carmen started in 2004. When the Ratatouille production pulled Peterson off the Up project for a while, Docter brought in Thomas McCarthy, writer and director for The Station Agent, who “took notes for six to eight months,” as Rivera puts it.

Russell's Multiple Layers
Russell’s multiple layers of clothing and Carl’s thick jacket and boxy trousers created unique problems for the cloth-simulation team to solve. At first, character developers tried making Carl’s hair thick, but it was too distracting.

“We spent a lot of time on the story,” Docter says. “The actual production was only during the last year and a half. It’s our 10th film now, and we have really good people who have honed their craft. We could push the production schedule.”

Carl Fredrickson

He’s three heads tall and square. His head is square. His trousers are big and boxy. Even the age spots on his hands are square. But, he didn’t start life that way. When he was only eight and first met Ellie, his face had a little roundness. Still, he and his family are obviously more rigid than Ellie and her family, as we see at their wedding. In their house, pictures of Carl are in square frames, while pictures of the two together are in square frames with an oval matte. After Ellie dies  and Carl stops selling balloons, all the circles are gone from his life, and his design becomes totally square. He withdraws from life. He’s boxed in, stuck in his ways. That is, until someone threatens his reclusive life in his homespun memorial to Ellie; and then, with the help of 10,000 balloons, he soars. For his adventure, Pixar provided a family of enthusiastic circles to soften the grouchy old guy’s edges.

The technical challenges for Carl were in rigging a cube’s facial expressions to show emotion, and in creating the silhouettes animators wanted despite his oversized jacket and boxy, wide pant legs. As a result, Pixar calls him the most complex character it has created.



As Docter, Peterson, and del Carmen worked to refine the story, production design began developing the visual language. “The story is about a house pulled by balloons floating in the sky,” Docter says. “We needed to create a world where that was possible. The story pushed us to a level of stylization we’d never done before.”

Ricky Nierva, the production designer, named the resulting look “simplexity.” “This is a movie about age, about the authenticity of life,” Nierva says. “Our big challenge was not to make it too photoreal. Otherwise, why not make it live action? On the other hand, if you pull too much detail away, it looks like cheap CG. So we looked for the sweet spots for characters, environments, and details.”

For design inspiration, the character and production designers chose the work of Mary Blair, a Disney artist who developed the color and style for Cinderella, Alice in Wonderland, and Peter Pan, and who was art supervisor for such films as The Three Caballeros and Saludos Amigos, set in South America. They also looked at George Booth cartoons, and Hank Ketchum’s “Dennis the Menace.”

To create storybook backgrounds, the artists used simple shapes for bushes in the jungle, eliminating any leaf that didn’t face the camera, and stylized the shading and modeling for Carl’s house. “We wanted Carl’s house to feel small, like a dollhouse,” notes Steve May, supervising technical director, “as if big hands made small pieces and placed them by hand.”


Clouds in the Skies

Carl and Russell travel in Carl’s balloon-powered house through skies filled with clouds in approximately 150 shots—fluffy, white clouds and dark, stormy clouds. The clouds are volumetric, constructed from spheres using a system developed by TD Alexis Angelidis. In the entire film, 400,000 different spheres create the clouds; the storm alone uses 85,000.

“Alexis can place a sphere, maybe even as large as a football field,” explains Gary Bruins, effects supervisor, “and then run a script that breaks it into a fractal distribution of spheres with different radiuses. The scripts helped with general modeling, but Alexis built the clouds by mostly adding sphere onto sphere.” The various-sized large spheres described the overall cloud shape; the smaller spheres added detail.

Each cloud model had two shader versions, one for the surface and another for the interior. The interior allowed object matting—the house, for instance—but no camera motion blur. The surface supported camera motion blur but didn’t allow embedded objects. “We had a switch that we could flip on a per-shot basis,” Bruins says.

To scatter light within the clouds, TD John Pottebaum created a 3D density map. “In addition to lighting artists using their tools and John’s 3D density map, Alexis replicated, in the shader, the lighting response of water droplets in the cloud,” Bruins explains. “And, his volumetric caching system was a huge help in optimizing rendering.” –Barbara Robertson

The trim around the fireplace doesn’t quite line up. The fireplace has soot, but if you look closely, you see that the soot is actually brush strokes made with a dry brush, as are the bark on the trees and the dirt on Russell’s face. “You’ll see this style everywhere in the movie,” May says. “We used a variety of procedural and paint components in the shaders, but generally we had a painted brush stroke in a paint pass with every shader.”

In addition to Carl, Ellie, Russell, and Charles Muntz, the main characters include a 13-foot-tall bird that emerges from the jungle after the balloon-driven house lands on a tabletop mountain in Venezuela. Russell names the bird Kevin, but the dog that also pops out from the brilliant jungle names himself: Dug wears a collar that translates his thoughts into words. Suddenly, Carl now has two “family members” circling him. Kevin is colorful and silly, with a round body and long neck, and Dug is an enthusiastic, overweight golden retriever/lab mix that loves everyone. Carl’s a tough old cookie. It takes more than one “buddy” to bring him back to life.

For the characters, modelers working in Autodesk’s Maya adopted a “less is more” philosophy. Carl is three heads tall with stocky arms and legs.  Russell is a little egg. Dug has a big, round nose. “We removed anything extra,” May says. The characters don’t have ear holes or nostrils, for example, not even Dug.

It was character supervisor Thomas Jordan’s team of approximately 30 people who had first turned the concept art, maquettes, and expression sculpts for characters into 3D models that could move and that met the design goals. Each of the main characters had its own unique problems to solve. “It was more of a challenge than usual to finalize these characters,” Jordan says. “No one can tell you what simplexity means. We had to find it. The sketches and maquettes didn’t work in 3D once we started animating them.”

Animators gave the riggers drawings of expressions they wanted to hit, and the riggers, working in Pixar’s proprietary software, shaped the mesh topology created by the modelers to match. “We set up the mesh so the rigging controls created the shapes the animators wanted,” Jordan says. “But in the case of Carl, we spent quite a bit of time and a lot of trial and error to give a square the ability to have human emotions that are not symbolically square.”

One problem was Carl’s mouth, which stretches in a hard line across his huge bottom jaw. “We had to make some compromises,” Jordan says. “We softened the corners, but we tried to do it in a subtle way so you would feel it without seeing it.”


Beautiful Balloons

The effects department’s role was to create the believable elements that connect the audience to the stylized world. “By animating the balloons in a realistic way, the audience more easily believes the house could float,” maintains Steve May, supervising TD. “When they buy that concept, they believe Carl is going someplace. And, when Russell shows up on his front porch, they believe he really is in peril. Our primary goal is to help tell the story. Our secondary goal is to make something beautiful.”

At first, knowing it would be difficult to run a rigid-body simulation on 10,000 balloons, Pixar tried to float the balloons procedurally within a modeled canopy. “They had no notion of each other, though,” says Gary Bruins, effects supervisor. “And, they intersected all over the place. It didn’t look good.”

TD John Reisch did tests using rigid-body dynamics with Open Dynamics Engine (ODE) through Autodesk’s Maya that produced the believable motion they wanted, but the system was able to simulate only 500 balloons. When Eric Froemling split ODE away from Maya, though, and created an improved, stand-alone version that ran in Pixar’s pipeline, they upped the number. Considerably.
With ODE installed in Pixar’s pipeline, Reisch created a system in Maya that generated the initial state of the balloon simulation, then moved that state to ODE as a stand-alone without using data communication. “Releasing it from communicating with Maya released the bottleneck,” says Bruins. “We could do 50,000 balloons, but because they weren’t intersecting, we needed only 10,000 to fill the canopy.”

The canopy provided artistic control for the overall shape of the grouping. “The simulation can push the balloons out of that shape, but when the rigid-body sim was in its rest position, it had the same topology as the canopy,” Bruins explains. Thus, to maintain the art-directed shape, the team decided to move the strings that tied each balloon to Carl’s chimney in a separate simulation.

“The strings are more complicated than the balloons because getting them to bend and conform around the balloons requires more control points,” Bruins says. “If all the strings had to avoid the balloons along their paths, they would become tangled and twisted.”

So, in the first pass, the crew simulated the balloons with strings that didn’t know about other balloons. Then, they brought that simulation in as baked data and simulated only the strings. “We thought about reducing the number of strings, but as it turned out, we didn’t have to,” Bruins says. “The strings collide and interact with surrounding balloons, but they don’t influence the behavior of the balloons.” For close-up shots, though, they would simulate balloons and strings together, and hand dress the hero balloons. –Barbara Robertson 

Cranky Old Carl

Animators working with Carl discovered that economy in motion matched his simple style. “We’d put his face in a pose and let the pose speak for the character,” says Scott Clark, animation supervisor. “Carl feels more alive if you don’t animate him than if you do. Sometimes, we’d just put a blink on him and not much else. He’s old. He doesn’t bend or twist too much.”

Animating Carl’s clothes, however, became a technical problem. To give viewers the feeling that he lives in a miniature world, the designers increased the size of the weave on Carl’s herringbone wool jacket to look as if someone had scaled up a doll’s jacket to fit someone five feet tall. “And, it isn’t just the textures,” says Jordan. “It’s the way the fabric moves, as if someone cut a doll’s jacket from a life-sized jacket. But nothing in real life looks like a scaled-up doll’s jacket. So we had to guess. Then, we worked with animation to do walk cycles, have him sit and stand and interact with Russell to see if he was believable and fit the design of the film. We didn’t want him to feel like a doll.”

In the end, Carl looks like a little old man in an oversized suit, a square, boxy shape with wide pant legs. And that caused problems with cloth simulation. “We wanted the miniature look with the oversized clothing, and to see the lines of action—the bends of knee, the lines of the elbow, the position of the shoulders relative to his head,” May says. “But, when Carl bent his little legs inside his big trousers as he walked, you didn’t see the knee bend with normal cloth simulation; it looked like he was walking with straight legs.

“Our animators got really upset,” May relays. “They’re used to doing subtle and important differences in poses to sell the acting of the scene.” To fix that problem and to give Carl’s clothes a thick look with a minimum number of wrinkles that the artists wanted, the cloth-simulation crew used targeting with modeled surfaces that the simulation would approximate, and shapes based on baked simulation that they isolated to certain areas of the body.

Holding onto Russell

The problem with Russell was his egg-shaped face. “He’s basically a balloon,” Jordan says, “and, my gosh, that was challenging. The smallest facial expression would change him and make him look too old, or too young, or not appealing.” Giving him a chin to separate his head from his neck helped, but often the riggers would make their best guess and then adapt the rig based on notes from the animators and directors.

“Russell is very caricatured,” Clark says. “And, he’s a kid, so he has to jump around and be active. But, if we moved his neck too much, he’d feel gummy, so we built limitations into the model.”

When Russell jumps around, he moves several layers of clothing—a shirt, a sash on top, a neckerchief on top of that, his backpack straps, and the backpack itself with between 20 and 30 Wilderness Explorer gadgets hanging from it, all animating independently. “For cloth, we have a two-stage process,” May says. “Animators perform the character without clothing, and then simulation does the clothing after they’re done. But the backpack is a rigid-body simulation that runs nearly in real time.” As the animators put Russell through his poses, they could see the backpack and all its parts moving, and because the software converts the dynamic movement into keyframe data, they could change the simulated movement.

Special shaders accented the ability of lighters to change host Charles Muntz’s expression from kindly to sinister.

“This is the most complex clothing we’ve ever done,” says May. “And then, we attach these two complicated characters, Carl and Russell, by a hose and a rope to each other and to a house that’s attached to 10,000 balloons. The animation rig is amazingly complex. Depending on how hard Carl pulls on the hose, it might move the house, the wind might push the balloons, and Russell is pulling, too.”

This is the situation: Carl has wound the hose attached to the house, floating above, around his shoulders. He’s tied a rope from Russell’s backpack to a knot on the hose. The tethers form an upside down “y” with the house on top. Because animators wanted control, they used a sophisticated rig to move the tethers, rather than rely on a simulation to create the motion. The house moves independently, sometimes reacting to balloon simulations, sometimes moving with keyframe animation with the balloons reacting to that.

“In most shots, we didn’t see all these things at once, but when we saw all three, generally animators performed the characters sans clothes and with the tether in a rough position for the house,” May says. “Simulation ran dynamics for the clothes and, if necessary, improved the animation of the tether. And, effects ran the simulation for the balloons and sometimes for the house.” In other words, animation first, then cloth simulation and effects working in parallel.

Carl tied a rope from Russell to a hose he’s using to pull the floating house. Creating the final image at top required water simulation (above, far left), character animation with rigid-body simulation for Russell’s pack and a sophisticated rig for the tether (above, second from left), cloth simulation (above, second from right), and shading and lighting (above, far right.)

Ellie Fredrickson

Carl’s wife, Ellie, is a circle. She has a tiny body with a balloon head, a little button nose, a beautiful smile, and bare feet. She’s bouncy. She wears hand-me-down clothes and has dirt under her fingernails. She’s Carl’s playmate and soul mate. Her photos in their house are in round frames, and everything about her is loving. We meet her as a young girl in the beginning of the film, during Carl’s back story, and we follow her life with Carl in one of the most emotional sequences ever created for an animated feature.

Carl’s adventure begins after Ellie dies: She is the underlying motivation. To carry Ellie’s spirit through the movie, production designer Ricky Nierva gave her a symbolic color, magenta, that shows up in flowers and skies, to remind us of her, and composer Michael Giacchino created a waltz as Ellie’s theme that plays with twists and turns until at the end, when it becomes an action-adventure theme.

Iridescent Kevin

Kevin, the bird, needed to be a character never seen before and dramatic enough to give Muntz, the pilot who was Carl and Ellie’s hero from the newsreel footage, a reason to spend 50 years looking for her. “She was the hardest character because we walked the fine line between too unreal and too cartoony,” Jordan says. “Pete said that when the audience first sees her, he wanted her to look like she’s made of gold when the sun hits her, but that she really could exist in nature.”

The art department found images of a Monal pheasant from the Himalayas that has iridescent feathers in metallic green, purple, red, and blue colors, a copper-colored tail, turquoise blue skin, and a blue crest like that of a peacock. The crew was able to see a pair in a nearby animal sanctuary, and those birds served as reference material for Kevin’s colors. Kevin became a 13-foot flightless bird with an orange beak, a long, iridescent blue neck, and purple feathers. “John Lasseter always says that before you can caricature reality, you have to understand reality,” Jordan explains. “To be believable, it has to be inspired by something that could exist.”

For animation inspiration, the studio brought an ostrich to the campus, and the animators took pictures as it walked around outside, but they weren’t bound by the real bird’s physical limitations. “Kevin is a made-up creature, and probably the character we had the most liberty with,” says Clark. “Russell uses her like a pogo stick. Pete always said that if you could hear the sound her brain made, it would be like a dial tone.”

For Kevin’s feathers, the technical directors used one Ri curve for the quills, with hundreds more coming off the sides to produce each barb. “For Finding Nemo, we modeled feathers using wide hair or a single piece of geometry with a clever shader,” May points out. “For Kevin, we wanted more geometric complexity. And, because we used individual pieces of geometry, we could model a range of feather types from flat feathers that we might have done with the shader before, and also fluffy under-feathers.”

To color Kevin’s feathers, the artists created a shader that gave the directors the ability to choose which colors turned on and off, and at which angles, as well as texture maps painted with a ramp of all the colors the feathers could exhibit, to control the iridescence. “The order in which colors appear in the map is the order they shift as the angle changes between the camera and the light source,” Jordan says. “It’s a fairly big cheat, but Pete wanted the ability to turn the iridescence off.”


Eight-year-old Russell, a Wilderness Explorer who inadvertently stows away on Carl’s adventure, takes Ellie’s place as a circle in Carl’s life. Russell rolls joyfully through life, excited, constantly circling around. He looks like a little egg with stubby arms and legs and no neck, and he wears a backpack loaded with Wilderness Explorer camping gear, a neckerchief, and a sash covered with Wilderness Explorer buttons.

The technical challenges for Russell were in creating facial features and expressions that looked appropriate on his smooth, young, oval face, and in simulating all his layers of clothing and gadgets.


Kevin is a rare, 13-foot-tall flightless bird, colorful and silly. Carl and Russell happen across her after they fly inside Carl’s house to South America. A supposed missing link, she is the object of (Carl’s hero) Charles Muntz’s 50-year-long quest. In Kevin’s shape and coloration, she, too, reminds us of Ellie: Kevin has a round body, a long neck, and brilliant iridescent feathers. The technical challenges for Kevin were those brilliant iridescent feathers.


Net Knots

In one sequence during the film, a character gets caught in a bolo net. To create that net, rather than using a sheet of cloth with a texture or geometry attached, TD Eric Froemling drew on the same rigid-body simulation system used to float the 10,000 balloons carrying Carl’s house.

“I had first played with this idea on a promo spot for Cars,” says Gary Bruins, effects supervisor. “There’s a shot where Mater runs into a velvet rope, and I tried connecting spheres to approximate the rope. I talked to Eric about the idea, and he gave it a shot.”

Here’s how it worked. “Eric strung together a series of spheres—rigid bodies—like a string of beads hanging in a doorway,” Bruins says. “With enough spheres, we could approximate the behavior of a rope. He made a net by knotting the ropes into a 2D grid. Any time a character interacted with the net, we got a more believable response from the rigid bodies than we would have with cloth. Because it had open squares, if a limb went through an opening, there was no motion on the net.”

To render the net, TDs ran Ri curves through the centers of the spheres and shaded the curves with rope textures.

Similarly, Froemling stitched together a series of triangles and made a quilt of rigid bodies to create a tarp that dropped onto the balloons. As a result, the TDs could more easily make the tarp interact with the rigid-body simulation for the balloons than if they had used cloth simulation for the tarp.

Bruins intends to keep exploring this use of rigid bodies to do soft-body simulations. “The nice thing is that you can easily detach the strings of spheres and get ripping and rupturing, so it has a lot of potential for large-scale cloth and special cases.” –Barbara Robertson

Barking Is So 20th Century

For the dogs, the character supervisors and animators spent time in a doggie day-care center, consulted a behaviorist nearby, and, of course, studied their own dogs. “If you look at their designs,” Clark says, “Dug’s nose is really big, almost a Snoopy nose. But we do things with the behavior of the rig to flavor the animation more toward realism. We have controls to give them that little flavor, but we consciously chose to do dog behavior.”

In addition to the happy-go-lucky Dug, the film features Muntz’s pack of hunting dogs, which he trained to serve him—even to the point of serving dinner, albeit somewhat sloppily. Where Dug is round and happy, the pack dogs are angular and serious. Alpha, a Doberman, leads the pack with Beta, a Rottweiler, and Gamma, a bulldog, right behind him. All the dogs talk via a high-tech collar that, among other things, translates their thoughts into spoken words. Peterson voices Dug and, with some technical tricks, Alpha. 

“Pete and I are lifelong dog lovers,” Peterson says. “So we looked for a unique way to have Carl and Dug talk. The collar allowed us to get the behavior of a real dog and hear its thoughts; Dug could be scratching his ear while he’s talking.”

The real behavior of Alpha, Beta, and Gamma’s pack, on the other hand, is often frightening, especially when they turn their hunting prowess toward Carl, Russell, and Kevin. But as we learn and Peterson affirms, “There are no bad dogs, only bad masters.”

The bad master in Up is Charles Muntz, voiced by Christopher Plummer, whose design is as angular as that of his hunting pack. “Pete’s challenge to us was he wanted the audience to feel like Muntz was a warm, loving grandfather, who could become sinister at the drop of a hat,” Jordan says. The crew accomplished that, in particular, by rigging his eyes and eyebrows to be appealing or scary, and through shading.
“Athena Xenakis was able to find the right shading details on his face, such as crow’s feet, that could be enhanced or hidden, and to make his eyes look sinister when combined with certain lighting,” Jordan points out. “When he’s holding a lantern and talking about his obsession with Kevin, we goosed the lighting to bring out the creepy details.”

Muntz—Carl, and Ellie’s childhood hero—forces the climax of the film. Carl learns what a well-rounded adventure in the circle of life really is, and always was. And, Pixar reminds us, for the 10th time, that the medium is deep enough to hold any story, whether funny, adventurous, scary, emotional, heartwarming, heartbreaking, heartpounding, or, sometimes, all of that rolled into one. That is, one meticulously designed and accomplished film named Up.


Like all the dogs in Up, Dug wears a high-tech collar that translates his thoughts into spoken words, but Dug is different from the rest of the pack. He’s round; they’re angular. He’s the happy-go-lucky nerd of the hunting pack, sent out by the others on a hopeless mission to get him out of the way. And that’s when he adopts Carl and Russell. For the animators, the goal was to give all the dogs realistic behavior, yet still have them fit within the caricatured style of the film.

Deep Emotions

For Pixar’s first adventure in Disney Digital 3D-land, the studio focused inward, turning stereo into a window, rather than lobbing gags out from the screen and into the audience. “We used [stereo] 3D to help tell the story,” says director Pete Docter. “When Carl is stuck in his house, we kept it flat, but when he’s standing on a cliff, we wanted to feel the wind on his face.”

Stereoscopic supervisor Bob Whitehill devised a depth script based on the color script. When Carl and Ellie are young and life is colorful, the images have depth. When Ellie dies and the color fades from Carl’s life, the images are flat. Then, Russell shows up. The scenes get deeper and deeper. Notes supervising TD Steve May, “Everything [at Pixar] has always been 3D, so, technically, it was just matter of adding a camera and rendering.”  –Barbara Robertson

Barbara Robertson is an award-winning writer and a contributing editor for Computer Graphics World. She can be reached at