Myth Labs
Issue: Volume: 33 Issue: 2 (Feb. 2010)

Myth Labs

Digital Domain, MPC, and other VFX studios harness computer grapgics tools to create effects in Olymian proportions.

For a teenager to think he’s a Greek god is probably not all that unusual, but in director Chris Columbus’s latest fantasy film, teenager Percy Jackson discovers that he actually is. A demigod, to be precise, the son of Poseidon. And he’s only one of many mythological beings living in the 21st century appearing in 20th Century Fox’s film Percy Jackson & the Olympians: The Lightning Thief.

Based on the first book in a series of adventure/fantasy titles by Rick Riordan, the film stars Logan Lerman as Percy Jackson. He and his best friend, Grover (actor Brandon Jackson), a satyr, it turns out, and Annabeth (actor Alexandra Daddario), who learns she’s the daughter of Athena,  must save Jackson’s mother (Catherine Keener), return a stolen lightning bolt to Zeus (Sean Bean), and prevent a war between the gods. Various mythological beings, including Hades (Steve Coogan), Medusa (Uma Thurman), hellhounds, a Minotaur, and a Hydra stand in his way.

It seemed impossible that the children could defeat the Hydra (shown at left and above), especially when one severed head grows back as two, until Digital Domain animators decided that the heads hate each other. Internecine squabbles gave the children a fighting chance.

Kevin Mack supervised the visual effects, managing the work of several studios that created more than 900 shots on a tight schedule. The start date for the film was April 2009; the release date is this month.

“When I first met with Chris, they were still writing the script,” Mack says. “We started working on the shots in postproduction before he finished filming, and Chris cut the film as he went. So, we’ve been at a dead run for a year now.” At the end of postproduction, 800 shots had made it to the finish line.

The primary racers were the artists at Digital Domain and MPC Vancouver (the Moving Picture Company), with crews at Luma, Pixomondo, Rhythm & Hues, Evil Eye Pictures, Trixter Film, Rise Visual Effects, Method, Slash FX, Whiskey Tree, and Image Engine also joining the marathon.

For previs, Columbus and Mack worked primarily with story artists at Fox in the studio’s Cinedev department, although Vancouver-based Image Engine helped as well. Columbus shot most of the film on greenscreen stages in Vancouver, then edited it, and did the digital intermediate work in San Francisco. Mack worked out of Columbus’s San Francisco offices.

“CineSync is a powerful tool,” Mack says, referring to the software program developed by Rising Sun Research that allows people to view and annotate the same image from various locations. “We were able to work remotely from a viewing environment in San Francisco, and you know, it wasn’t that different from working in the studio. You look at pictures and draw on them, and that’s kind of how I like to work, anyway.”

Of the 800 visual effects shots in the film, Digital Domain artists created approximately 320 and the crew at MPC close to 170. The rest of the studios worked on the other 310 shots, with Luma handling 88 of those, including Medusa. Uma Thurman plays that mythological creature; Luma added the snakes, dozens and dozens of snakes of all types and sizes, that cover her head. “It’s stunning,” Mack says. “They have the snakes rubbing against her, caressing her. Animating the snakes was a ton of work. But, they did a fantastic job.”

Also, artists at Whiskey Tree fashioned a 3D matte painting for eight shots that established the exterior of Mount Olympus. “It’s just beautiful,” Mack says. “They took the idea of creating a floating rock with monolithic Greek buildings and built on it. The shots are amazing.”

Percy Jackson, a demigod son of Poseidon, can use a fluid simulation to shield himself with water, or even use the water as a weapon. Digital Domain artists controlled the CG water.

The crew at Rise Visual Effects in Germany created set extensions for the interior of Olympus that required lots of little tricks to match scales. “The gods are 30 feet tall, so Percy and Annabeth are little bitty people in that room,” Mack says. “And, Rhythm & Hues did a great shot of the hillside under the Hollywood sign crumbling and opening up to form the entrance to hell. Pixomondo did Hades underworld exteriors. All the studios were so great. They bent over backwards and made sure we had something good for every shot. This is the best reel movie I’ve ever worked on.”

On Mack’s “best reel,” though, some of the most complex CG shots would be those created at Digital Domain and MPC. “Digital Domain did the Fury, this winged creature that’s crazy scary, and then, of course, the Hydra is awesome, and they did a huge water effect for the end of the movie,” Mack says. “And everybody loves [MPC’s] Hades.”

Furious Fury, Horrifying Hydra
The Fury is a kind of she-devil with three sets of wings that she uses to fly around a classroom before grabbing Percy. Cloth simulation moved her translucent wings, and animators used spline controls and shape animation to drive her horrifying facial expressions. “In a few areas we asked our modelers to tweak the shapes on a shot-by-shot basis to make it work,” says Dan Taylor, animation director. “She’s only in nine shots, so we didn’t do much R&D with her, but she’s pretty cool.”

The dragon-like, five-headed Hydra, on the other hand, required a larger effort. It forms from five security guards who melt into one creature. “We have them step close until they rub shoulders, then they fuse into the Hydra, and their heads grow out of a slimy placenta,” describes Mack.

The crew pulled color schemes and face shapes into the creature’s heads. “We made one black and another light skinned,” Taylor says. “One is chubby, and another has a round face.” But, each head looks more like a cross between a crocodile and a T. rex than a human.

Character designer Aaron Sims also gave the 20-foot creature backwards-facing, T. rex-like “arms.” “When it’s just born, we see a claw, then a foot, and then we have a nice reveal of the whole Hydra shaking off birth slime, with the center head breathing fire,” Taylor says.

The animators’ design dilemma was determining how the five heads would move. “Chris Columbus and Kevin Mack said the heads should be like junkyard dogs in attack mode all the time,” Taylor says. “So, we had to come up with reasons why, if it was so fierce, it didn’t win and eat the kids.” The answer was to have the heads hate each other.

“They’re always knocking each other out of the way,” Taylor says. “When they’re in the Parthenon-like museum, the heads come around the columns, trying to get the kids, but the ones on the right want to go one way, and the ones on the left want to go the other. And, just as one head is about to bite the kids, the others pull it away. It was really fun to animate.”

To manage the complex model, animators working in Autodesk’s Maya had windows for each individual head, with rigging controls for the eyes and jowls. “We were modifying the rigging through the entire production,” Taylor says. “It was a constant back and forth.”

Although the creature is hand-animated, procedural animation controlled a set of fins that fanned out and vibrated as a head prepared to strike. In addition, dynamic simulations wiggled the skin, and a separate layer of animated displacement maps created folds.

“The Hydra is so real,” says Mack. “We have a shot where Percy flies up in the air with his winged shoes and cuts off all five heads with his magic sword.” He thinks he has killed the monster, but it stirs and rises up. “The necks tear apart,” Mack continues, “and reform into two solid necks with strings of goo between. New heads squeeze out of the necks. And, now it has 10 heads. It’s horrible. It’s one of my favorite shots.”

 The reptilian faces with crocodile eyes don’t show much emotion—the character design was sinister enough. But, the animators could expand the inside of the middle heads to shoot fire and use controls on the animation rig that gave them a proxy of the fire.

“I was never concerned about the performance,” Taylor says. “I had a veteran group of animators who had come off Transformers. So it was fun to explore and focus more on the secondary animation—the wiggles and jiggles that give life to the models. It definitely shows in the finished product.”

Art-Directed Fire and Water
To send fire shooting out of the Hydra heads, Digital Domain used a gas simulation run through Side Effects’ Houdini. “The fire had the highest resolution simulations that we’ve ever run,” says visual effects supervisor Kelly Port. “We sometimes used terabytes for one simulation, so the detail was really nice.”

The primary water simulation happens during the film’s climax. The sequence starts on an Empire State Building observation deck, built as a partial set in Vancouver, British Columbia. Digital Domain extended that set and provided a 360-degree view of New York City below with a matte painting created from tiled photographs sparked with bits of moving traffic and other details. “I think it was close to 30k wide,” Port says.

Luke shoots at the side of the deck, causing Digital Domain to create a little rigid body  dynamics (RBD)-driven destruction. Then the two actors fly on wires over glass rooftops, duck into a construction site, fly out from there, and land on the rooftop. Percy summons the water tanks to explode. The water forms a circle around Luke, and then crashes on top of him.  

Once they knew Percy and Luke’s flight path, an environment team at Digital Domain took a half-million digital still photographs or so from rooftop locations around New York City. “As we planned the shoot, we’d send our location scout Google Earth locators by e-mail,” Port says. “He’d use those to go on scouting missions, talking to landlords and building managers, to find places where we could go up on the roofs.” The team organized the photos they took by shot and location, and then projected images onto low- to medium-resolution geometry organized in Nuke, lit the buildings, and rendered reflections. For the Empire State Building, they added ambient-occlusion renders.

To put the flying kids into the shots, layout artists at Digital Domain tracked the images in Nuke, stabilized them, and then projected them onto cards that the animators could move through space in Nuke. When young Olympians land in the construction site, the actors landed on a greenscreen stage; the actual site was CG. “It’s night, and Luke is shooting the lightning bolt, so electricity is hitting the pipes,” Port says. “It’s very strobey. It looked great.”

On stage, the actor used a long, swordfish-shaped prop with LEDs along its length. Digital Domain artists tracked that and added arcs made from thin geometry procedurally animated in Houdini and rendered as a bright core light with additional glows added in 2D. The arcs loop around and branch out to give it the feeling of a tesla coil.

“Luke [actor Jake Abel] is about to take out Percy with the lightning bolt,” Mack says. “But, Percy, being the son of Poseidon, has power over water. So, we have this crazy water thing. Percy forces the water out of the towers and then down onto Luke to short-out his lightning bolt and win the day. The idea is predicated on controlling a fluid simulation, and Digital Domain did a fantastic job.”

Artists at MPC Vancouver created Hades out of digital charcoal, filled his cracks and crevices with molten lava, and set his wings on fire.

To cause the water to first form around Luke like a torus, Digital Domain’s effects artists used a controlled fluid simulation. “We wanted to balance the physicality with the magical notion that Percy is making the water hover in space,” Port says. “The trick was to make it look as if magical forces pushed onto it from different directions and forced it into different shapes.”

In fact, that’s how the effects artists directed the simulation: Control fields pushed the digital water into different shapes. “Imagine that we had powerful fans pushing a ton of water up into a shape that floats in the air,” Port says. The artists could have the fans—that is, the control fields—push on the simulation or not, but in any case, the digital water behaved physically correctly within the zone of the simulation, Or, “correct-ish,” as Port puts it.

Transition Trick

Early in the film, Poseidon walks out of the sea at Coney Island, a shot created at Luma. He’s 30 feet tall and made of water. As he walks down the boardwalk, he turns into a normal-sized man. “Chris wanted him to scale to normal size and become human as he walked, but I didn’t like the idea,” says Kevin Mack, visual effects supervisor. “So, I suggested having a rippling wave go through him that transforms him into a man-shaped body of water. Billowing chunks of water blow back to the sea, and as he walks, he refines back to a man.”

To set up the effect, Mack shot two motion-control plates, one as if the actor was 30 feet tall and another as a six-foot man, and then scaled the camera move. “The big thing about transitions where you have fluid flowing into one form or another is the handoff from the live-action element and back,” Mack says. “So I suggested using procedural noise to warp the live-action element at the same frequency and amplitude as the fluid. If you do that and then, just as you start to bring it in, you have it warpy and swimmy, it keeps it from feeling like an abrupt transition. And, generally, I do an articulated wipe, again using noise, to form little spots that grow where you’re bringing through the final resolved live action until it covers the whole thing. That way you reveal through to the live action, but the live action you reveal is warped, and you animate out of the warp as you dissolve it. As the last of the water effect goes away, so does the warping of the live action. It’s a wonderful trick, and simple, too.”

Similarly, to create a water wall during the Hydra sequence, the artist used the same types of forces to push the water up. “The Hydra is about to get Percy, so he breaks a water pipe and creates a wall of water,” Port says. “The Hydra is on one side breathing fire against the water wall, and Percy is on the other.”

The water, created with Digital Domain’s proprietary fluid simulator, works through Houdini. By simulating the water first and surfacing it, the team had geometry for the fire to react to. “The fire bounces off the wall and spreads out,” Port says. “It’s pretty forgiving because the water is choppy.”

Although the team rendered this effect through Houdini’s Mantra, most renders moved to Nuke through Pixar’s RenderMan.   “For this show, we updated our fire- and water-simulation tools, and made big improvements in the environment workflow through Nuke,” Port says. “But I love the fact that we were able to do some great character work with the Hydra.”

Hellfire and Hades
For its part, MPC Vancouver created five characters. Two involved leg replacements—Percy’s friend Grover is a fawn, and Chiron (Pierce Brosnan) is a centaur. A crew of approximately 20 artists and animators working in London handled those characters using techniques and technology refined during their previous work on Narnia.

The other three characters were a 12-foot-tall Minotaur, hellhounds, and the 12-foot-tall Hades created by a team of nearly 75 in Vancouver. “A big challenge with these characters was the overall musculature,” says visual effects supervisor Guillaume Rocheron. “We worked hard to position the muscle and skin systems correctly and move them right.”

The large size of the Minotaur and Hades, and their close interaction with Percy, also created challenges. “These characters weren’t always framed far away,” Rocheron says. “They were big in scale, but they interacted closely with Percy. You could see details as small as skin pores.”

To make this detail believable and possible to animate, the crew created two models for each character. One was a low-resolution model. The low-res Minotaur, for example, had 50,000 faces. The second was a high-resolution model created with Pixologic’s ZBrush. The high-res Minotaur had 200,000 faces.
“We wanted a dense wireframe so we could do blendshapes on small details,” Rocheron says. “Rather than painting a vein in ZBrush and extracting the displacement, the modelers created blendshapes on the high-resolution model.” 

The character developers skinned the low-resolution model, which allowed for quicker iterations, and animators created the performance using that model in Maya. Then, the team moved the high-resolution ZBrush model to Maya and used a wrap deformer to have the low-resolution model drive it. In other words, the high-resolution model moved using the low-resolution model’s performance. In addition, the artists layered a static displacement map on top.

That system worked for all three characters, but Hades, which is made of lumpy, cracked charcoal, with lava oozing in the cracks, had an additional complication: He appears out of a bonfire. And fire envelops his wings.

“We see the fire close up,” Rocheron says. “So, we spent a lot of time trying to get the simulations to be in as high resolution as possible. Generally, fire is on a large scale, and what matters is the overall motion of the fire, not the details in the fire. But, this fire is big in terms of scale, and it’s in front of the camera, so you can read the details within the fire.”

Thus, rather than simulating the fire at a resolution sufficient for overall motion and then using 3D textures to add details, the effects artists decided to run the simulations at extremely high resolution. “Usually, we simulate fluids at a voxel size of five to ten centimeters,” Rocheron says. “This time, we brought the size down to a millimeter, or less on some shots.”

The crew used Scanline’s Flowline software for the simulation. “The good thing is that with the last version of Flowline, we aren’t limited to a bouncing box for the simulation,” Rocheron says. “The software builds the volume as the fire expands.”

Going to Hell
When director Chris Columbus asked visual effects supervisor Kevin Mack to brainstorm some ideas for a sequence in which Percy Jackson goes to the underworld, Mack created a drawing on a marker board of Los Angeles with chasms. “The idea was that as they’d fly in a boat to the underworld, they’d pass by all this personal stuff—hats, wallets, diplomas, old photographs, walkers, guitars, and so on,” Mack says. “I did a huge drawing, and Chris loved it. And then before anyone could photograph it, someone erased it to put up the new schedule.”

With Mack’s idea in mind, Pixomondo developed previs and then created the shot using 3D matte paintings, CG objects, and photographs. The crew filmed the actors in a boat dangling from a crane on a hydraulic rig.

“We went to a prop house in Vancouver and shot tons and tons of things from all periods,” Mack says, “cell phones, old typewriters . . . it all floats in a kind of river in the sky. As Percy passes through it, he grabs a pocket watch. When he looks down, he sees thousands of lost souls on pillars or rocks, and one pillar in the middle with Hades’ mansion on it modeled after the Hearst Castle. The dock at the mansion and the doorway façade is a set. The rest is all-CG.”

Crowding the Face
A second challenge for Hades was that the character sometimes looks like actor Steve Coogan, and sometimes like the big, burnt, lord of the dead, and this CG version needed to perform with Coogan’s expressions. To create the performance, the crew used Mova’s Contour Reality Capture system.

“We captured Steve [Coogan] saying all the lines of dialog and doing a range of facial expressions using the FACS system,” Rocheron explains. “Then we retargeted the 593 control points to our Hades model, and they drove the deformation of the skin. We wanted to avoid going through a blendshape system. We tried to keep as much of the original performance as we could.”

In addition, to tweak Hades’ performance in areas and for angles they couldn’t see in the captured performance, the crew used Alice, the studio’s crowd software system. “When you animate crowds, you work with motion-capture clips and the software figures out how to blend them together,” Rocheron says. “So we used the crowd software to blend motion-capture clips and to work with layers of animation. We could use a clip from a performance on one part of the shot and another clip from the second part of the shot, and blend them together.”

Luma fastened the snakes onto Uma Thurman’s head and animated the creatures as if they represented Medusa’s multiple personalities. They adore Medusa, caress her, and rub her cheeks, but when she decides she wants them to turn someone to stone, they rear into a synchronized performance.

For the fiery skin, the artists converted the fire simulations into point clouds in Pixar’s RenderMan, and used RenderMan’s color-bleeding functions to apply color from the fire onto the character. “Usually, you have lights around a character, but for this character, the main light source is his fire,” Rocheron says.

Rocheron counts art-directing the fire as the biggest challenge for the show. “The fire was such an important component of the character,” he says. “But art-directing fluid simulations in a precise manner is very difficult and tricky. When Hades leans forward, we needed the fire to grow in that direction. When he’s angry, the fire needed to move faster. It took time to identify which components of fire made the difference, but once we found the rules, it became quicker.”

“This project has so many choice bits,” Mack adds. “It’s just jam-packed with incredibly amazing characters and shots. Chris Columbus allowed us an amazing freedom to contribute creatively to this project, and these facilities did great work.”

Although the ambitious CG characters will likely have the biggest impact on audiences, visual effects artists will more likely remember the creative application of fluid simulations and the seamless work. Not to mention the fact that these artists produced all these effects in less than a year.