Flushed with Success
Issue: Volume: 29 Issue: 10 (Oct 2006)

Flushed with Success

Sometimes the simplest things are the most difficult. Take, for example, Roddy, Rita, Toad, and Le Frog, the stars of Flushed Away, the latest feature film from Aardman Animation and DreamWorks Animation. These characters might look as if modelers created them from plasticine in the same workshops where Wallace and Gromit took shape, but they are every bit as computer-generated as Shrek, Fiona, and Donkey.

Flushed Away follows Roddy (Hugh Jack­man), a sophisticated, pampered mouse living in an upper-class Kensington flat until he’s flushed down a toilet. He lands in Ratropolis, a version of London, built in the underground sewers from rubbish. It’s as quirky and detailed an environment as Aardman fans have come to expect, but bigger, filled with water, and populated with thousands of characters—mostly rats, snails, toads, frogs, and bugs. Roddy, of course, wants to go home. He tries to persuade Rita (Kate Winslet), a savvy rat with a boat, to take him back to his home, but he’s thwarted by the villainous Toad (Ian McKellen) and Toad’s cousin, Le Frog (Jean Reno).

The film represents the third collaboration between Aardman and Dream­Works, which began with Chicken Run. Produced by Aardman’s Peter Lord and David Sproxton, and DreamWorks’ Cecil Kramer, Flushed Away blends Aardman’s stop-motion style and DreamWorks CG techniques; it’s Aardman’s first completely CG feature. Sam Fell, Aardman’s director of commercials, and David Bowers, a story artist on Shark Tale and senior storyboard artist on Wallace & Gromit: The Curse of the Were-Rabbit, co-directed Flushed Away.

From left to right: To create a freezingwave of water, DreamWorks effectslead Scott Cegielski simulated UVswith particles (1) and rendered the UVparticles as a texture map (2). Whenthe foam traveling down the waveof water hit the ice, a wipe with 3Dtextures, it froze (3, 4). An expressionin Maya grew icicles (3, 5).

“We were going to do this film in stop frame,” says Fell. “In the end, there was so much water in the film that we would have had hundreds of effects shots. It would have killed us to do that in stop frame, whereas in the computer, it’s straightforward. But, it was so bizarre: While we could have a thousand rats and a boat chase in the water, the difficulty was in getting the [characters’] little brows to move right.”

And eyebrows, as any Aardman fan knows, are very important. “When you watch Aardman films, it looks simple, but what they do is horribly subtle,” explains Martin Costello, the character TD supervisor who worked on rigging the Flushed Away characters.

Simple, But Not Easy
Gromit provides the best example—he doesn’t have a mouth; the animators convey his facial expressions by moving his eyebrows. “In A Close Shave, Gromit spends 30 seconds just acting with his eyebrows,” Costello says. “They’re pushing and pulling and making dents above his eyeballs, moving ever so slightly between the keyframes, and it’s magic.
“We have characters with [Gromit-like eyebrows] the likes of which we’ve never rigged before,” says Wendy Rogers, visual effects supervisor for Flushed Away. “The directors wanted to be able to press down and leave an indentation in the eye socket. It was quite noodly.” 

To rig the Flushed Away characters’ eyebrows in Autodesk’s Maya so that the DreamWorks animators could replicate what Aardman animators do in plasticine, Costello’s team took a layered approach. Animators could pull the eyebrows into a rough silhouette using three sets of joints—left, right, and middle. Then, with additional controllers, they could flatten the front of a brow or plump it up to make it fatter.

“They essentially sculpted the [digital] clay,” says Costello. “We also had a plug-in that allowed them to do deformations on a low-resolution surface that we’d bind onto the final geometry.” Thus, animators could work more quickly by weighting a few points on lightweight models and then transferring the performance to the higher resolution geometry.
Creating the characters’ mouths was equally challenging. For their stop-frame animations, Aardman modelers typically create a set of approximately 16 plasticine mouth shapes for each character. And then, once the animators apply the shapes to the models, they can push the “clay” around. “The plasticine is infinitely malleable,” says Fell. “But in CG, the mathematical lattice keeps breaking if you push in too many directions all at once.”

Shown at left is Roddy’s skeleton with mouth and hand controls. Atcenter is the simplifi ed model that animators used. A shaper causedthe low-resolution subskin, which was attached to the skeleton, tomove the high-resolution geometry. At right is the fi nal render.

Supervising animator Jason Spencer-Galsworthy, who was a model maker at Aardman for Wallace & Gromit in A Close Shave and a key animator for Chicken Run before joining PDI/DreamWorks to work on Shrek and Madagascar, helped develop the mouth system for the Flushed Away characters. “We used Toad because he had to roll his lips all around his head and he speaks asymmetrically,” Spencer-Galsworthy says. “He’s very expressive and has a massive amount of surface. We knew if we could get Toad to work, we could get any character to work.”

Rather than building a facial system based on muscles, the team decided to emulate Aardman’s method: They built replacement mouth shapes. “We spent six months working with the Aardman animators, trying out different approaches,” says Costello. “Normally when we do a rig, it uses a muscle-based system based in reality. But the plasticine puppets don’t have muscles.” Thus, each Flushed Away character had a set of 10 or more replacement mouths created by the modeling department; Toad had between 25 and 30. “It seemed like the only way to go, really,” says Spencer-Galsworthy. “The mouths needed to be sculpted accurately by model makers.”

Using special rigs, the CG animators could mimic the wayin which stop-frame animators performed the eyebrowsand mouths of plasticine characters. Here, Flushed Away’sWhitey holds Roddy and Rita, as Spike shows his anger.

The animators could mix percentages of the resulting sculpted blendshapes in Maya. But they did so judiciously. “Even though you could dial-in degrees, you wanted to hit the pure shape as closely as possible,” says Spencer-Galsworthy. “In keeping with the plasticine techniques, when you replace the mouth, it’s an extreme change, and then you soften the movement off.”

To soften the movement, the animators used controllers around the mouth to change the shapes. “Basically, there’s a little ribbon around the lips and a thick ribbon that goes around the cheek to give it a plasticine look,” says Costello. “Animators could push the CVs on the ribbon.”

Fast Rigs
There are eight main characters in Flushed Away, 10 secondary characters with major roles, and a host of background and crowd characters, some of which speak a few lines. Because the modelers and riggers created the characters in sections, and because all the characters used the same rig, a custom Maya plug-in glued together different components to quickly rig new characters. “The posh way of putting it is that we have an inheritance-based mix-and-match system,” says Costello. “We rig separate components and use those to rig new ones. By the end, we could do a background character in less than half an hour.”

To build a character, the riggers started with pre-made components. “We’d click a button, and all these joints would pop up that we could pull around the screen to position,” explains Costello. They added behaviors to the joints that would, for example, allow an elbow to swell a bit. Next, they added the subskin, a cylinder made of rings that the riggers shaped and scaled to create bulges. And then they painted the binding. “You can pull the points around and then save out all the CVs of the skin position,” Costello adds. “The binding determines how the subskin drives the high-resolution geometry.”

For the characters’ bodies, the riggers again matched the simplicity of the Aardman characters, but not rigidly. “At first we over-engineered the spine and had to back off, but we put a little stretch on the arms and legs,” says Costello. “You don’t notice it a lot, but without it, we got popping. And Rita can tilt her hips, which makes her a bit more feminine.” That helped give these characters a different performance than that of the plasticine puppets. “We pushed the style,” says Spencer-Galsworthy. “We wanted to capture the essence of Aardman animation and then be true to where it’s going to go in CG.”

For example: There’s a 30-second shot of Toad talking to a tadpole. The animators created it early in the process using what Spencer-Galsworthy calls “hard poses.” “It came back because of voice-track changes after the style had developed,” he says. “So we pushed the animation into the new style. We still had definite poses, but we added a bit more fluidity on the way.”

In the Bubble
Fell made sure that the style varied from character to character, though, by giving the animators guides for each of the main characters that illustrated frequency and range of movement. He literally drew a bubble around a character that showed how far that character could stretch its arms.

“Some films have a style that applies to all the characters,” Fell says. “We looked at Madagascar, which has a snappy, cartoony, American style of animation, and all the characters move according to those rules. But the Aardman style is more that each character has its own particular way of moving that’s related to its characteristics.” Thus, Fell created a spectrum of movements and defined each character’s range within it: how broadly they moved, how far they could move, and how busy and quick they were.

Toad, for example, who Fell describes as flamboyant, aristocratic, and operatic, had a wide bubble to show his larger-than-life movement. On the other hand, Whitey (Bill Nighy), Toad’s toady, who is a slow-thinking character, moved within a smaller bubble. “He’s like an armoire on legs,” Fell says. “He lumbers along like Preston in Close Shave. But then I wanted Spike, Andy Serkis, to move quickly all the time and have a little twitch. He was at number 10 on the frequency range, and Whitey was at the other end.”

Similarly, the characters’ appearances mimicked the Aardman puppets but didn’t replicate them exactly. “It was an evolution, not slavish duplication,” says Rogers. “They wear foam clothes and look like plasticine, but we didn’t add thumbprints. That seemed a conceit.”

Ratropolis and the Mob
The crew wasn’t at all modest about building the character’s environment, however. “Our main set is 72 feet in diameter in physical rat space,” says Rogers. “It was great to give the directors that scope.” If the directors had used stop frame rather than CG, they would have relied on matte paintings or made the sets smaller.

As a test, DreamWorks duplicated in CG a set that Aardman had built. “Ratropolis is built out of rubbish, so we built a section of street and a row of shops from old furniture, broken cocktail sticks, buttons, and other junk,” says Fell. The city that DreamWorks built also used rubbish, but CG rubbish, of course—forks, chains, bottle tops, and ultimately thousands of other 3D models. Although most feature animations at DreamWorks have around 1500 to 1700 unique models, according to modeling supervisor Matt Paulson, Flushed Away had over 3000—from the sophisticated buildings aboveground to an underground duplicate made of trash. Set dressers drew from libraries to populate the middle grounds and backgrounds with pre-built models.

Because the rats would have built their city out of trash, DreamWorks fashioned its
teeming underground duplicate of London using 3000 3D models.

“The thing that makes me laugh is that our set cost us our time, but the materials were almost free,” says Fell. “We used an old sardine tin for one of our cars. But at this fabulous, wonderful, completely CGI studio, it cost thousands of dollars.”

On the other hand, stop-frame animators couldn’t have populated the hand-built set with thousands of cosmopolitan rats. “We had every shape, size, and color of rat walking about living their daily lives,” Fell says. “We couldn’t do that in stop animation.” Nor could they have animated a boat chase that splashes through Chinatown and other Ratropolis locations. “We would have had to change the story completely,” says Fell.

Head of effects Yancy Lindquist led teams of TDs and effects leads who created the cast of extras, Rita’s boat, the Jammy-Dodger, the water, and other effects. For crowd simulation, DreamWorks runs a proprietary rule-based system, dubbed MOB, which they modified to use Maya as the front end. “That was the best choice to get the characters up and running quickly,” says Lindquist. “We’d start with one character, animate a cycle, and then copy the cycle to another character and tweak it. The rigging was set up so that the cycles could be copied easily from one to another.” A mix-and-match system for paraphernalia helped add variety.

Because modelers created each tiny piece in Rita’s boat, the Jammy-Dodger,lighters could rely less on textures to show details.

Once the TDs had fitted the characters with paraphernalia and motion cycles, they positioned them in a scene and drew curves to indicate paths for the characters to move on. In one shot, rats might be milling around in an amusement park and climbing onto rides made of teacups, and in another, waiting in line for a red, double-decker boat or wandering in and out of shops. “We’d try to set up all our curves and avoidance rules for a single master shot—one scene, all the characters,” says Lindquist. “We’d populate the walkways and waterways, and run the sim through all the shots, and make sure it was working. Then we’d shoot it with various cameras. It was like having a group of extras milling around that you’d shoot from different angles.” 
Fluid Mechanics
The biggest challenge for the effects team, however, was the water, and one of the biggest challenges in creating the water was the scale. “Roddy is 10 inches tall, so when we created water and splashes, we had to keep it in scale with the character,” explains Lindquist. “Sometimes we’d push the scale to make a wave or a boat feel as big as possible, though.”

For fluid simulations, the crew used the studio’s award-winning proprietary software and developed special tools, particularly to animate splashes created by characters (see “Character Splash System,” pg. 16). “The effects are the bad guy on the screen,” says Rogers. “We had to make the water more graphic than real, but it had to be real enough to be a threat.” For rendering, the crew used PDI/DreamWorks’ proprietary rendering software.

“We basically used two techniques for the water,” Lindquist says. “For droplets that fell off characters, when Wendy [Rogers] and the directors wanted an iconic shape, we’d model those shapes. Otherwise we worked with the fluid simulator to mold the water into what we needed.” By adjusting the number of particles and how high they’d leap up from the water, for example, the effects team could create specific spiky-looking splashes.

At five minutes and 123 shots, one of the longest water-effects sequences in the film, and the wildest, was a boat chase. Roddy and Rita are on the Jammy-Dodger, a cross between a tugboat and a James Bond speed racer that is made from parts of old cassette tapes, a trumpet, tennis balls, goggles, a small window fan, and other bits and bobs. “It’s driven by expressions in Maya,” notes Lindquist. “We set up defaults that made the whole boat shake, but we also turned up the engine and controlled various parts.”

Each boat in the high-speed chase created a different type of splash that moved with the boats as they tore through the sewers. “We had eggbeaters making splashes, and boats causing rooster tails in the water,” says Alex Ongaro, effects lead. “The sequence took three people six months of development time and then eight months of production.”
The difficulty was making the splashes and the water look connected. The team created the splashes using Maya particles for the base simulation. Then, they exported the simulation to the studio’s proprietary software. “With our software we could get fast renders with 10 times the particles, with more density,” says Ongaro. “We could light them with real lights.” The water was created with geometry and displacement.

“The problem was that we had to start on the effects before the water was lit,” explains Ongaro. “We had to create the splashes before the geometry was delivered to rendering, yet do a reflection of the splash into the water and use the color from the water on the particles to connect the two and make them match.”

Thus, the splash makers found a way to duplicate the color of water onto the particles. To fake reflections, they mirrored the particles on the Y axis and used distortion compositing in DreamWorks proprietary node-based compositing software to put the reflection in the water. “Most of the time the effects team took care of compositing,” says Ongaro. “The effects, color correction, and blur were done by effects animators.”

As with Aardman’s plasticine characters, the Flushed Away directors
wanted each CG character to have its own performance style.

Effects lead Fernando Benitez had a different kind of water problem. In a dramatic sequence, Rita, Roddy, and the Jammy-Dodger are heading for what Benitez calls “the perfect storm.” “They’re heading for a waterfall, and there is turbulent water with threatening waves,” he says.

To create the water, Benitez started with a surface from the layout department that described the water level. “We used displacement maps on the surface to create the waves, with fractal noise to get foam on top of the water,” he describes. “Inside the lighting package, the displacement maps gave the lighters the motion surface descriptions of foam and water.” Because the displacement happened inside the lighting package, to give animators an approximation they could use to make sure a boat contacted the water surface, the TDs applied the same maps to the geometry.

For the waterfalls, the effects team layered three categories of splashes—spherical splashes, crescent shapes, and mist, all created with particles.

Ice Ending
Toad dispenses with the population of Ratropolis by spraying the characters with liquid nitrogen, which turns them into rat-cicles. Roddy and Rita turn this to their advantage: In a climactic moment during the film, they spray liquid nitrogen on a giant wave of water about to engulf a crowd of rats, and it freezes. 

“I didn’t want just a simple wipe,” says effects lead Scott Cegielski. Instead, he used the foam texture around the wave surface. “By simulating the UVs with particles, I could use the UVs to control the texture map, apply it to the surface, and it would travel down the surface to a frozen state,” he explains. “Then I’d render those UV particles as a texture map, and use that to tell the renderer how to apply the foam texture.”

In other words, the foam traveled down the wave and, when it hit ice, it froze. “The ice is strictly a roto,” Cegielski says. “It’s a wipe with 3D textures, with a particle effect on the leading edge.” To create icicles, he used an expression in Maya that started growing icicles when the texture map hit the crest of the wave.

The DreamWorks riggers, effects artists, and animators learned new tricks to create a CG evolution of stop-frame animation, while Spencer-Galsworthy picked up some tricks from the CG side. “That’s why I came over,” he says, “to improve my animation, and I definitely did. You can push your animation and revisit it. The finesse is amazing. And, working with different styles and different animators increases your breadth of knowledge. I’ve really learned a lot from the animators at DreamWorks.”

The admiration is mutual. “It was great working with Aardman,” says Costello. “They really know how to animate. They’re mad as hatters.” 

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