Speed Chills: Ice Age: The Meltdown

How the Cool Tools Devised by Blue Sky Studios Created Twice the Toon in Half the Time

Global warming has hit ’toonland — during Fox’s Blue Sky Studios’ feature Ice Age: The Meltdown, the prehistoric characters spend most of the film escaping from an oncoming flood. That's presented its own challenge for the filmmakers, because animating water is one of the trickiest tasks in CG.

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The crew of artists creating the film had to hit the ground running, too. “We had to do the movie in half the time,” says director Carlos Saldanha, who quickly warmed to the task. “It wasn’t an easy decision, but when the studio asked if we wanted to face the challenge, everybody said, ‘Let’s do it.’ The team was motivated — they loved the story and they loved the characters.”

Saldanha, who had co-directed Ice Age and Robots, the studio’s first two features, and directed “Gone Nutty,” an Oscar-nominated short, was ready. “The good news was that we had a solid script up on reels,” Saldanha says. “Every sequence had to work. We pounded on the story every day. We didn’t have room for mistakes.” At the end, the script was so tight that there were no outtakes for the DVD. “Sequences went from the edit room to the animators. We didn’t have time to rethink the dialog.”

The team streamlined all the other areas of the production as well, from modeling through animation and rendering. Last year's Robots was a testing ground for new technology that made Ice Age: The Meltdown possible, but when the studio turned up the heat on the schedule, the crew devised new technology and techniques especially for this film. “We had an adrenalin rush for a year,” says Saldanha.

Beauty on the Surface

Having familiar characters to work with saved the crew some time in character development: All the lead characters from the original Ice Age returned: Manny the mammoth (Ray Romano), Sid the sloth (John Leguizamo), Diego the lion (Denis Leary), and Scrat the acorn-loving squirrel (Chris Wedge). However, the modelers created around 35 new characters with multiple variations for migrating herds and 40 environmental sets that included more than 150 different types of trees. In addition, the modelers had to convert the original characters from NURBS models into subdivision surfaces.

Blue Sky bases its modeling, rigging, and animation system on Autodesk’s Maya. For rendering, though, the studio relies on its own CGI Studio, sophisticated ray tracing software that incorporates an object-oriented graphics programming language. The renderer and other software tools have been in development since the studio’s founding in 1987.

“We’ve developed a unique workflow,” says technical lead Eric Maurer. “The founders, and [CTO] Carl Ludwig in particular, have developed robust solutions that are physically accurate, look correct, and work correctly for the user with very little intervention.”

For example, Blue Sky’s ray tracer can bounce rays off Bezier patches rather than, as with many ray tracers, only polygonal faces. “We have our own subdivision representation — hierarchical subdivisions that are all parametric patches, continuous curves,” explains Ludwig. Thus, rather than create characters in NURBS and then convert the patches into smooth surfaces made with ever-tinier polygons, the modelers now work with subdivision surfaces.

“The subdivision surfaces gave us a lot of advantages,” says character rigger Steve Unterfrantz. “We no longer have to worry about seams, pinching, and tearing where the NURBS surfaces touch each other. It was a challenge for the animators to create the same performances for the [returning] characters using new models and rigs, but there were so many savings in other ways, it was the logical thing to do.”

Also, although dealing with curving patch intersections is a more complex problem for a ray tracer to solve than bouncing rays off thousands of flat surfaces, rendering the patch-based surfaces takes less memory, especially when a ray tracer has to calculate secondary reflections and refractions.

Moving Right Along

To meet the accelerated schedule, the modeling, rigging and animation departments devised methods to speed their workflow. For new lead characters, modelers used templates from a Polhemus scanner. To create multitudes of characters, riggers created variations from generic models. Character riggers also developed modular rigs and Mel scripts that assembled the modules into characters. The modular approach not only sped the rigging process, it meant that animators could more easily move from character to character.

Sixty-five animators worked on Ice Age: The Meltdown — nearly double the number on Ice Age — and only eight of them had animated the original characters. “Four or five of us set up libraries for the new animators that showed how a character moves and why it moves that way, to make sure the other 55 or 60 people always stayed on model,” says Aaron Hartline, an animation lead.

Animators worked on a shot-by-shot basis, creating performances for all the characters in a shot, rather than following individual characters. And they worked fast. “We were so focused, so direct, it was almost like we stuck with the first gut instinct that came out,” says Saldanha. “I’d say, ‘OK, this is the scene and this is what we need. Go, go, go, go. We didn’t overthink or second-guess. I think that rawness of the idea is there and that’s what I love the most.”

Hartline, who led the animation for Scrat, agrees. “We had to trust our first approach,” he says. “We’d just tweak that raw performance to get the best out of it. There was something good about that, something fresh.”

Shades of Fur

Nearly all the characters in are furry or feathered. With Blue Sky’s fur system, groomers set parameters for guide hairs that control the hair’s style; the system then procedurally generates millions of hairs on the creatures’ coats using these parameters. It’s a typical fur-grooming system. However, three things about the fur system stand out: procedural motion is rigged into the guide hairs, no texture maps are used, and a voxel-based system renders the fur.

Rather than using a simulation engine, a system called “follow-through,” which was developed by Adam Burr, calculates the fur’s movement by predicting a result based on previous motion. Animators control stiffness, the amount of follow-through, and something Maurer calls “settle time.”

“We also use gravity and wind vectors,” Maurer says. “But the engine isn’t solving the problem from a dynamics point of view. It’s solving it almost from a probability point of view. You need a team of people to finesse a simulation engine. This tool is automatic.”

To color the hair, technical directors used procedural shaders rather than painted texture maps, an approach that was tried successfully on Robots and implemented throughout Ice Age: The Meltdown. “You could probably count on two hands the total number of texture maps in the whole movie,” says Brian Hill, materials technical director (TD). The procedural shading system uses a Maya interface over a custom-node based network and compiles the shaders in Maya. Plug-in splines describe areas for color, noise creates textures, and TDs used nodes to create such other material properties as specular highlights and roughness.

“We avoid maps unless we need them,” says Ludwig. “They take up memory, they have to be repainted, and they’re more difficult to work with.”

Developing a network of nodes can be time-consuming, but unlike texture maps, the procedural shaders can move from character to character. “I created a procedural material for a condor’s foot — layer after layer of procedural elements that gave the nasty-looking claw foot fine, cellular detail,” says Hill. “Then, I used that same network for the other foot, for the condor chicks and with a little variation for all the other birds. It takes more time at the beginning, but it’s much more modular than maps.”

To render the fur, in keeping with the studio’s philosophy, a new volumetrically-based fur system accomplished two goals: the fur looks three-dimensional and the lighters’ job became easier. “The lighters might use separate lights for the characters to help them stand out from the background, but they didn’t need to do any special grooming or use separate lights for the fur,” says Ludwig. “The volume-based lighting model was integrated within the lighting system, so it acts properly with lights in the environment and with shadows and global illumination. When you get something that works right all the time, you need to do less special stuff to make it look right.”

Maurer provides another time-saving example, this one from the materials side: “Most 3D packages have specular and diffuse sliders,” he says, “but in the real world, specular and diffuse have an inverse relationship. So our materials usually need only specular. Diffuse is calculated from specular.”

Water World

Melting ice creates water, of course, which meant Blue Sky had to create gallons of CG water, from a water park showcased at the beginning of the film to a threatening flood. “We know water is hard to animate and control in CG and expensive to render” says Rob Cavaleri, effects supervisor. “Our challenge was to blend physical reality with a directable caricatured style for our cartoon world. We managed to pull it off in a year.”

They did this with a combination of deformable geometry that emitted particles to create splashes, with procedurally animated surfaces based on physical models of waveforms, and with simulations created with Next Limit Real Flow software. Special rigs attached to characters emitted bubbles as characters swam through the water. To create froth, during rendering a system written in the CGI Studio language automatically generated particles around characters and objects such as rocks, and created a mesh around the particles to have a renderable surface. “We could tell it how long the froth lived and how swiftly it moved,” says Cavaleri. “The animation was all procedural; the particles moved along wave surfaces automatically. We would never have managed without these clever techniques.”

Ready, Set, Go

In most scenes, the water was contained within sets that ranged from icebergs to grasslands to forests. Few matte paintings were used — modelers created most of the sets. For Ice Age, the modeling department built the sets on a per-shot basis from the camera view as described in the layout. Despite the short timeframe, for Ice Age: The Meltdown, modelers created complete environments that had some details even in areas where the camera wasn’t expected to go. “When we were working on the first Ice Age, sometimes the director wanted to move the camera where there was no set,” says Shaun Cusick, co-head of modeling. “There were lots of charge-backs to other departments and it slowed things down. So for this one we tried to build the set as an entire environment.”

The voxel-based method used for fur also rendered grass, and procedural shaders also textured the environments. Thus, rendering the environments became an interesting technical challenge that was solved by staging the geometry from complex in the foreground to less complex in the distance. It was only one of many challenges as the team raced to the finish line.

“We were on our toes to the end,” says Matt Simmons, animation technical lead, who fed shots from the animators into the rendering system. “We were going 150 percent the whole time. There was no ramp-down. But luckily, everyone was great and it was fun. I already miss working with Carlos.”

And what about Saldahna, who has directed three features and a short film in little more than five years? “I think when everything is done, I’ll be standing alone in a room saying, ‘Hello — anyone? What shall I do?’ It’s a miracle. It’s one of those amazing things. Those guys ... it’s extremely emotional for me."