Issue: Volume 33 Issue 9: (October 2010)

In Fine Feather

By: Barbara Robertson

After all the fuss and feathers died down in the 2007 Oscar race, live-action director George Miller's Happy Feet, a CGI film about dancing penguins, won best feature animation. It was the first full-length animated film created at the Australian studio Animal Logic and the first for Miller. But Happy Feet was chicken feed compared to the project Animal Logic recently completed: creating dozens of realistic owls for the CGI film Legend of the Guardians: The Owls of Ga'Hoole, directed by Zack Snyder and released by Warner Bros.

 "Everyone thought we pulled a one-off," says Ben Gunsberger, who was CG supervisor on Happy Feet and again on Legend. "They'd say, 'Oh, they got an Oscar, but will they ever produce anything as visually stunning again?' But, Legend was an order of magnitude more complex."

The story follows a young barn owl named Soren. Kidnapped by evil owls that want to control the world, Soren escapes with four other orphans. The fugitives then journey in search of the Great Ga'Hoole Tree where, legend has it, the knight owls live. "The bad guys are all about conformity, about the same species again and again," says Damien Gray, character supervisor at Animal Logic. "The good guys are about diversity, about individuals celebrating what each individual brings. The Great Ga'Hoole Tree is a large community of owls, and we wanted to have enough distinctive looks to support that story. So, we have just about every species of owl represented."


Owl Change

Of the 10 primary owl characters, three are Barn Owls, two are Great Grey Owls, and five are unique species-an Elf Owl, Burrowing Owl, Whiskered Screech-Owl, Boreal Owl, and Greater Sooty Owl. Secondary characters include three Short-eared Owls, an Eared owl, two Snowy Owls, a Great Horned Owl, a young Screech-owl, plus another Burrowing Owl and two more Barn Owls. Several varieties of owlets and owls are tertiary characters, as are additional species of animals:  bats, crabs, a mouse, a moth, and so forth.


Animal Logic created 70 characters for Legend of the Guardians: The Owls of Ga’Hoole, including
representations of most owl species.

"We produced 70 different characters for the film," Gray says, "Of those, a number had a re-dressing to change their color and patterns, and another 30 characters had extra surfacing. We had 100 different surfacing variations."

For example, to create two main bad characters, the crew started with a generic Long-eared Owl, which was a "good" character in the great tree, and then made hero variations by painting the species with red and black designs. "We used the same model and rig with new surfacing," Gray explains.

To sculpt the various species of owls, the modelers began in Pixologic's ZBrush, working from reference photos and with concept art that showed each owl from the front and side. During the design process, the crew treated each owl species as a unique model; each had its own 3D maquette with painted details. In addition, each hero character had two versions. The modelers, still working in ZBrush, sculpted one owl with its wings closed and another with its wings open, as if it were flying. Once those versions received approval, the modelers moved into Autodesk's Maya.

"Ultimately, we had one model and one rig, but the modelers used the perched and flying versions as a benchmarks to be sure they could achieve the transformation between the shapes," Gray says. During this process, which continued over several months, the artists wisely identified seven main body shapes and sizes that they eventually refined to three topologies, ending up with three models and seven body shapes.

These models and shapes formed the basis for all the species of owls in the film, but the overall number of models still grew. "We had at least three geometries per character, and some had four," Gray says, "a low-res version for animation blocking, another for animation, a third for lighting, and some characters had a fourth version that we used for collisions, to smash particles against."

Most CG characters have surfaces created with displacement maps, texture maps, and sometimes hair and fur. These characters had feathers.

"The bald version of an owl is a skinny, chicken-like creature," Aiden Sarsfield, CG supervisor, describes. "The volume and thickness for the owls comes from their feathers."

The crew created two types of feathers. Animators controlled the primary feathers, which connected to the wings. The character effects team controlled the secondary and downy feathers, which they generated procedurally.

For each type of owl, modelers created 60 primary feathers, 24 for each wing, and 12 for the tail, and delivered them to the rigging team. After Happy Feet, the riggers offered the animators a number of options for improving the rig, and based on these responses, they rewrote the underpinnings of the system (see "Happy Feat," November 2006). "We kept the look and feel of the rig we used for Happy Feet," Gray says. "But we completely overhauled the internals."

As did the modelers, the riggers needed to achieve flying and perched versions of the owls within one rig per character. Once they had developed a generic articulation structure, the riggers put each component--the wing, leg, spine, and so forth--into a library.

"We rebuilt each character's rig from the ground up using shared, common components," Gray says.

The surfacing artists also worked with two versions of each bird, grooming one pose with the wings open in a T-pose, as if it were in flight, and another with the bird perched with its wings closed. "The real trick in making the deformation look right was having the surface transition as well," Gray says. "Animators could pick whether the feathers were neat and tight in a perched pose, or looser in flight, and the surface would transition with the character while it was moving."

 
At left, the R&D department developed a new system to meet the primary technical challenge for the film: creating and moving the owls’ feathers. At right, surfacing artists re-groomed the warrior owls, giving them helmet hair to keep their feathers from poking through the helmet as they moved.

The animators had approximately seven controls on each arm, that is, the bird's wings, and an additional 10 to 15 on the feathers. "They could bend and curl and cup individual feathers to simulate the force of wind," Gray says. "On top of that, they could rotate and translate individual feathers if they wanted."

An automated review system provided renders for the secondary feathers so the animators could review the final performance of the fully feathered birds before the owls moved on to lighting.

"We could do our reviews in context without involving all the departments," Sarsfield says. "The animators would check [the performance into the pipeline]. The procedural animators would cache the motion onto geometry for the performance. The cache would be loaded overnight onto a set with the camera, and we would generate all the renders so they'd be ready for the animator the next day." The procedural system worked for other departments as well, with each selecting the features to turn on and off. Layout, for example, might want depth of field on and feathers off.


Growing Feathers Procedurally

To create realistic secondary feathers and a downy surface, an R&D team led by engineer Daniel Heckenberg created a new system appropriately named Quill. "We rewrote our feather system from the ground up," Gray says. "It was a massive undertaking. We worked closely with R&D almost up to a few months before delivery to get the control and features we wanted from the system they wrote."

For each bird, surfacing artists within the character effects team hand-placed approximately 1000 guide feathers and defined specific parameters for each feather. The parameters defined such aspects as how quickly the feather becomes smooth and uniform as it moves up from a scraggly base, the length, the width, and so forth.

"Almost every property was a parameter that an artist could modify," Gray says. "We had quite a number of prim vars--primitive variables--per feather, 50, maybe 100, to define the look."

Quill then interpolated roughly 25,000 feathers from these guide feathers, generating all the barbs and curves on each. "We had 4.6 million individual curves," Gray says. "The analogy would be a fur system on top of a fur system with hair strands coming off each individual hair strand."

The artists began with Noctus, Soren's father. "We picked him because he is a hero character and he represented a class of characters," Gray says. Gray counted 99 versions of the high-resolution groom for Noctus on the road to perfection.

"We'd do a version, check it in, and then go back," Gray says. Once the artists decided they had the features they needed for the feathers from R&D, they moved on to the other characters. "We went full steam into production of the other characters to achieve the same level of detail," Gray says. "It wasn't that we had the luxury of getting one character working and then moved into production. We were delivering assets for blocking and pre-lighting at the same time. But, Quill development went on to the end, and the designs didn't allow us to cheat."

As Quill generated the millions of individual curves on the thousands of feathers, it transitioned between parameters set by the surfacing artists on the guide hairs. "We would get a lot of variation between two feathers, say one on the top of the head and another halfway down the back of the neck, because Quill interpolated all the prim vars between the two. We got smart about placing the guide hairs to get transitions where we wanted them."

Once the birds' performance was in place, a first pass of simulation provided basic deformation and movement, with Quill adding such secondary motion as wind effects. A second process worked to untangle any intersections. "We tried to do that procedurally," Sarsfield says, "and it would work in some cases. On top of that, we could apply individual guide controls. Or, we could kill individual feathers."

Although all that might sound straightforward, it wasn't that simple. "Initially, the pose-based deformations would be nice and clean, and then it came down to how the surfacing artists placed the 1000 guide hairs, how big they were, how long, how wide, and then how Quill interpolated them across an area," Gray says. "It was an iterative process working our way through all those rules." In addition to the geometry transitioning from a perched state to a flying state, the feathers needed to transition as well. By grooming each state separately, the grooming artists could be sure the feathers were in the right place.


At top, modelers, riggers, and surfacing artists created perched and flying versions of each owl to use as benchmarks. At bottom, the owls fly through painted and volumetric skies, and over landscapes in various levels of detail.

One of the key elements in the transition between the perched and flying states was the bird's neck, and for this, the riggers built an automatic deformation into the rig. "The neck would transition and deform naturally from the almost cigar torpedo shape in flight, to the upright state where it had to bend 90 degrees and look bipedal," Gray says. "Also when they're perched, they can turn their necks about 280 degrees."

To check for intersections, the crew put each character through 500 frames of calisthenics every day for six to eight months. "It was a daily process with modeling, rigging, and surfacing," Gray says. "The owlets were fluffy and soft, so we got away with more intersections. But, we'd see every little intersection on the adult characters with high-contrast patterning, like the Barn Owls. So, it was a lot of work."


Fly Through

"Without a doubt, our biggest challenge was feathers," says Sarsfield. "But the other challenge was the environments. We took the environments for granted at the start, but we had to step up our pipeline. We have a huge amount of detail going on--large forests, thousands of props, and expansive worlds."

Greg Jowell, who led the environments team, describes detailed rooms leading to vast, complex landscapes rendered from a bird's-eye view that include objects the birds land on.

"One of the bigger challenges in the beginning was deciding what we'd see from a bird's level," Jowell explains. "We did a lot of early work with the art department to determine if an owl flew at this average speed, how much distance it would cover and what we'd want them to see. Obviously, the film has a bit of a fantasy style, and we did things that wouldn't actually happen that way, but for the most part, the environments feel real in a stylized way because of the richness of detail."

Knowing that the story could change, the artists built the sets in layers, leaving the final polish until the cameras were set. New asset management tools helped distribute pieces of the environments to people who needed to work with them, and new LOD tools helped the team manage resources.

"We had four levels of detail for the forest," Jowell says. "That meant the artists hand-built the trunks and stems on all the semi-hero trees so we could control the look of the species. Then we placed procedurally grown foliage."

The artists started working in Maya's Paint Effects to develop the initial spread of branches and leaves, a technique they also used for bushes and smaller plants. Then, they saved that information in Animal Logic's in-house shading system, using proprietary shaders to apply materials and textures.

"Every limb of the Great Ga'Hoole Tree is like a forest," Jowell says. "It has multiple layers of plants--vines, ivy, moss--all this crazy stuff." Because the foliage is procedural, the artists added wind at render time that rippled through the vegetation.

Most of the environments in Legend are organic, even those with architecture of a sort constructed by the owls. "The idea was that if this was constructed by anything, it was constructed by ancient owls," Jowell says. "So there are slight owl shapes in the designs. There are a lot of carvings and the sense of an historic coliseum, but it is all rubble."

Jowell's team discovered that creating an organic environment was more difficult than they had expected. "Rocks, in particular, have erratic flows," he says. "They don't have lines that complement each other, but they do have a specific look, and it's obvious when they don't look right. Surfacing-wise, it's all challenging." As much as possible, the crew relied on procedural surfacing, with hand painting to add details.

To make it easy for the animators to load the complex environments, the crew provided maps. "We broke the environments into sections," Jowell says, "and for every environment we passed along for a scene, we passed along a section map to give the animators an idea of what was in the background that they didn't need to be concerned with." To animators working on scenes, the forest trees and vegetation could appear as bounding boxes to lighten the scene.

For the far backgrounds, the team used matte paintings. "In some places, we projected matte paintings on top of geometry, and every time we see the sky, we're seeing a combination of volumetrics and matte paintings," Jowell says. "The artists painted a lot of sky backgrounds. But, the owls fly through volumetrics."


Setting the Atmosphere

Nearly every sequence in the film has some kind of atmospheric effect--clouds, fog, fire, and other volumetrics. "People thought we were mad," says Miles Gree, one of three effects leads on the film. "We were starting a film and didn't have a fluid system for fire or smoke. But, two years later, we had a fully working pipeline. It was a major achievement."

To handle the fire and other volumetrics, Animal Logic's R&D team created an in-house fluid-dynamics system they call Snap, for the 40 effects technical directors on the film to use. "They wrote it from scratch using SIGGRAPH papers," Green says, "and added it to ALF (Animal Logic Fundamentals), a node-based procedural system." To achieve the high-resolution detail for fire and smoke, Snap distributes the simulations on 32 to 64 processors.

"The fire on this film is amazing," Gunsberger says. "I haven't seen any other film with the kinds of fire effects we have. Especially in stereo."

Green describes one scene in which an owl surfs a wall of fire curved like a wave.

"The Snap developers would start with a regular expensive fire simulation and then pushed velocities around in a curve," Green says. "We used a lot of wavelet turbulence so we could run the simulations at low res to check the bending and that it was moving at the right speed, then we added detail to get a defined shape."

For rendering, the crew used Pixar's RenderMan and the studio's proprietary Maya-to-RenderMan software, called MayaMan, and a proprietary shading environment. "We've always had a node-based approach to shaders," Gunsberger says. "Rather than having shader TDs write one shader with many controls, our shading system builds networks from components. If we have particular shaders with complex networks, like the feather shaders, we will give that to a shader TD to optimize and bake out as a single shader."
ALF created the feathers on the fly at specified levels of detail, drawing every barb and feather with curves when close, and slowly changing the detail to flat geometry as the bird moves away.

 "We also used image compositing extensively," Gunsberger says. "If there were slight animation tweaks, we didn't want to re-render volumes. We rendered deep passes, sampling data along the entire depth of the pixel."

Whether Legend achieves the same success as did Happy Feet remains to be seen, but for the crew at Animal Logic, the work achieved is a feather in their caps. "Every time we were asked to do something, like the fire or the feathers, we'd think, 'This is impossible,'" Green says. "But we carried on and went forward another step."

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

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