It's called Maze Runner, Sue," said Director Wes Ball to Visual Effects Supervisor Sue Rowe. "We've got to make them run."
And, run they do. The teenagers who try to escape a maze built with 100-foot-tall walls that rearrange themselves every night, and the Grievers, huge, multi-legged creatures that want to kill them.
The Twentieth Century Fox film, based on a series of young adult novels by James Dashner, stars Dylan O'Brien as Thomas, a teenager caught in a postapocalyptic world. Filmed in a large field in Louisiana and on stages, the story takes place almost entirely inside a glade in the center of the giant maze that has trapped several boys. When the doors to the maze open, brave boys run through trying to find a way home. But, the doors close without warning, trapping them inside the walls. And they never appear again. Once a month, an elevator appears through the ground and brings food, supplies, and another boy. One day, it brings a girl, who causes everything to change.
Visual Effects Supervisor Sue Rowe moved to Vancouver from London and joined Method Studios to work on the film. Once there, she began recruiting a core team to help with the Grievers; Method was known more for environments and effects than creature work.
"Wes [Ball] was telling me about the opening scene, and he was so excited that, within seconds, I wanted in," Rowe says. "I wanted this job. But how would we make this creature? As soon as I got the word, I contacted Erik De Boer, who had just gotten an Oscar for Life of Pi. And then I managed to persuade James Jacobs, who had just gotten a Sci-Tech Award [Science and Engineering Award], to leave Weta and come back to Canada, where he's from."
De Boer became animation supervisor, and Jacobs began working on a muscle simulation system that would help animators make the grotesque creature believable (see "Creature Simulation," page 20).
Lighting artists at method incorporated shadows and raking lights to give the computer-generated walls scale.
On location, actors worked near a 40-foot-long, 16-foot-tall wall with heavy, concrete doors, and in the studio, a smaller set on a bluescreen stage. Stunt actors played the role of the fearsome Grievers. Artists at Method grew the existing walls to 100 feet, created more, covered the walls with ivy, eventually destroyed sections of the maze, and replaced the stunt actors with the CG beasts.
Because the glade was green and the maze was covered with ivy, Rowe decided to use bluescreen on set rather than greenscreen. But, the camera used for the live-action photography was an Alexa. "It was my first time working with an Alexa," Rowe says. "After I had told everyone, yes, we'll go with a bluescreen, I realized that the Alexa responds better with green. I called Eric Brevig, who I had worked with on John Carter, and told him I needed his help."
And with that addition, Rowe had her core team. Brevig was on set for most of the principal photography and stayed on afterwards.
"Having Eric on set was great," Rowe says. "He's so experienced. We got great keys."
All told, a crew of approximately 150 artists at Method created 530 shots for the film, of which 150 were creature shots. "The creature was the fun thing and the main thing to talk about," Rowe says. "Next are the maze and the maze destruction, which happens at an integral moment in the movie."
The studio artists use a tool set that includes Autodesk's Maya, Side Effects Software's Houdini, The Foundry's Nuke, Adobe's Photoshop, Pixologic's ZBrush, Pilgway's 3D-Coat sculpting software, Chaos Group's V-Ray, and the proprietary software developed by Jacobs and his team.
The beast is a biomechanical creature with a slug-like body and six metal legs.
At one point in the movie, the audience sees 12, but is led to believe there are lots of the nasty creatures. "They're all the same breed but with a slightly different body," Rowe says. "The thing about the Griever is the cussed nature of it. Dashner describes it having metal legs and spikes, and blowholes down its back that make a wheezing noise when it expands its slimy, fatty tissue. We knew we had to freak people out a bit; it comes at the kids and nothing stops it. I had to go to dark places about the things I disliked [with the creature]."
Towering over the kids in the film, the creature is 12 feet tall and 22 feet long. The production team supplied concept art from Creature Designer Ken Barthelmey, and The Third Floor provided previs.
"When Rhythm & Hues went funny after Life of Pi, I looked around and realized that after 17 years at one company, it might be fun to change," De Boer says. "Method said they had a project for Fox and showed me the concept art. The sketches were stunning. The creatures were predatory, mysterious, scary, ready to pounce. It looked really fun and exciting. They said they were shooting in two weeks. I jumped on it."
The Method designers made a few changes to the concept art to add detail, but kept the broad strokes.
"It has an organic body without eyes," De Boer says. "It's a slug-like creature with a bulbous head, several rows of shark-like teeth, and two organic arms at the front like a T. Rex that we used to emote with, to give a feeling that it was sensing its environment. It has a scorpion tail and centipede-like knives with pincers. The body is mounted on a metal chassis with six legs. Its lungs drive the legs' pneumatic hydraulic actuators; its heart pumps oil through all the hoses connecting the metal parts to the legs."
The front legs have four joints, and the middle and back legs have three joints, and each leg can change size.
"We realized that these guys had to perform in the open field, the glade in the middle of the maze, but they also are guardians of the maze itself," De Boer says. "The maze has narrow alleys, so we gave the creatures telescoping legs. They can reduce their leg size and length to move within the maze walls."
Moving the Beast
A team of 11 animators led by De Boer performed the creature. "We looked at ants because, with a macro camera, they strike cunning, cocky, even predatory poses," De Boer says. "We also looked at cockroaches and grasshoppers. I like keying off nature to find cool poses I might not get from scratch. But, we ended up with a creature that was too insectoid. We had a huge machine in a narrow maze with a clunky drivetrain. We needed a more robotic feel. It also had to be agile and fast enough to be 'throw the popcorn out after you scream' scary. Finding that balance was great fun. We really wanted to go for a raw, dirty, ferocious, threatening performance."
Eventually, the crew found the right blend of spider-like and robotic movement, and developed several motion styles for the creature depending on its speed and location.
"For me, it was especially important to justify the way the creature locomoted within the maze," De Boer says. "Since it was designed to be in there, it would make use of the walls and be able to corner really fast. Yet, at the same time, we had to make sure it couldn't catch the kids too quickly. We needed the threat and the buildup."
Also important was finding the balance between the firm parts of the body around the metal parts and the upper, slug-like body.
"We gave the organic part a rib cage and skeleton, muscled it up, and then ran complication simulations to get the skin to behave properly," De Boer explains. "In the area where there are blowholes, we wanted the mass to be loose and wiggle and jiggle. We loosened up the shape and had fun with it in silhouettes."
Director Ball, an animator and visual effects artist, worked with the animation team to get the performances he wanted for the Grievers.
"He really understands what we do and how we work," De Boer says. "It was funny. We'd be in a room and he'd go from this calm, respectful guy to acting like a huge monster running around. He'd say, 'Something like that,' and then calmly sit down again. It was awesome. Intimidating, but inspiring. He inspired us to go big and bold with these creatures. We could really key off the aggression and energy."
Rather than animating pose to pose, De Boer prefers blocking out scenes. "When you do animation that's all about hitting the true physicality and realism in the weight, if you go pose to pose or use stepped poses, you get a distorted feel of energy when it's interpolated," he says. "I like to block out scenes with simple choreography, with the main central mass fully interpolated, so you get the idea of mass through the scene and the momentum."
Sometimes, though, poses made sense. "With the legs, we focused on appealing poses and cool silhouettes because we wanted the creature to be aggressive and predatory," De Boer says. "We looked for opportunities to get a strong negative space, strong poses. That's what we showed to Wes [Ball] as our first pass at animation."
To give animators a leg up with the centipede-like zipper knives, Rigger Victor Barbosa created optional procedural tools the animators could use to control when the knives opened and closed and how active they were. Barbosa also created a powerful rig to control the tricky telescoping legs. With those tools, animators created the threatening performance for the character, and even some emotional moments.
"We had a shot where someone throws a lit oil torch at a Griever," De Boer says. "We had to express that he was in pain before he recovered and started chasing again."
For that shot, Rowe filmed fire elements but found they didn't work as well as she had hoped. "So, when we set him on fire, it's all Houdini," she points out. "The fire wraps around its legs, burns its body, and the Griever screams in terror."
The first time we see a Griever, the animators reveal only its silhouette as they lower the monster down a wall behind Thomas. Thomas leaps across a huge gap from that wall to another covered in ivy. The Griever hesitates and then jumps on the wall next to Thomas.
"We sell that by having the ends of the pneumatic legs find purchase and friction, but it doesn't work well for him so the legs slide and bring the ivy to the ground," De Boer says. "There was practical ivy on the set, but we replaced much of it with full-CG ivy to properly tangle up our creature and have him tear it away. We also added chipped rocks and dust passes."
Walls of Ivy
While De Boer's creature animation team wrestled with the Grievers, Rowe's team of visual effects artists constructed the 100-foot walls and covered them with ivy.
"We were able to do some live-action shots, but as soon as they moved the camera back, we were off the set," Rowe says. "There were no live-action shots of moving walls; they were fully CG. And halfway through the film, when the kids realize they're in the center of the maze, there is a big reveal of a maze that's fully CG. You see that outside the maze, it's all barren land. In the center, it's green. All the walls are at least 100 feet tall, and they all have vines growing over them. That was something Wes Ball really liked, and it was one of our challenges."
At first, the artists used Houdini to create procedural creeping vines with thousands of tiny leaves, but in the early tests, the ivy looked too procedural.
CG artists grew procedural ivy on the digital walls and had the leaves turn toward the sun.
"The main thing about the way ivy grows is that it has tiny fingers that travel into cracks and wrap themselves around bits of material," Rowe says. "So we created a new tool. We could draw a line and have it wrap around something, and from that, grow leaves. And of course, ivy leaves turn toward the sun, so we could define where the sun was and have the leaves turn in that direction. Our ivy was so good that in places we replaced the original ivy because ours looked better."
Because the film takes place in a postapocalyptic world, the walls look industrial.
"Wes wanted symbols on the walls as if they had been used for some kind of nasty nuclear testing, but we don't know what," Rowe says.
At the beginning of the film, the walls are close together, but as the kids move into the undiscovered area, the walls move wider apart.
"Wes [Ball] was smart about how he shot the film," Rowe says. "Sometimes the kids would just hear the sound of the walls moving as the maze rearranged itself. It rapidly got more intense as the danger came upon the kids. When the moment came that the maze rearranged itself to kill the kids, we had 20 to 30 shots with a tsunami wave of destruction and the kids diving out of the way."
The effects team again put Houdini to work to create the destruction. On set, the actors ran across a floor on a bluescreen stage. Method artists simulated the floor cracking as they ran, and added layers of fine particulate dust.
"We showed Wes the test and he said, in his English accent, 'Yeah, that's bad ass,' " Rowe says.
The crew also used particle systems - in Nuke rather than Houdini - to make the environment in the glade more convincing by filling the air with bugs. This happened after Rowe, who had worked in London before moving to Vancouver, spent time on location in Louisiana.
"I have never seen bugs as big as the ones in Louisiana," Rowe says. "They scared me. Big ones with wings and little black buggers. The horse flies were the worst. I was in the middle of a field when one bit me, and one of the guys said we should make digital bugs. I took him up on that, and it was great. We built a library of bugs in Nuke and had them circling around. That extra layer of reality gave movement to every shot."
The most difficult thing about the maze, Rowe notes, was not the walls or the ivy, but it was making the walls look convincing. "CG can let you down when you want convincing scale," she says. "The artistry came from our lighting team and our great CG supervisor. They created lighting that gave the walls grandeur with a lot of shadowing, raking lights, and light traveling through the ivy."
Because many shots take place at night, the lighting team also needed to find ways to show the Griever, which has a dark-green body verging on gray.
The big reveal of the entire maze is entirely CG.
"V-Ray lent itself really well to the Griever," Rowe says. "We could get translucency in the fatty tissue and subsurface scattering - the comp team got that right through many layers. And, lighters put silhouetting lights behind so we could pick out his surface in this dark environment. That was a bit of artistic license, but we could see him nicely."
With this film and with Rowe's guidance, Method established itself as a place where artists can create convincing CG characters as well as convincing environments.
"This wasn't a big-budget movie compared to John Carter," Rowe says, referring to the film for which she was previously a VFX supervisor. "But, I couldn't think of a better team."
Creature Supervisor James Jacobs moved from New Zealand back to his home country to develop a system at Method that would help make the Grievers believable.
"It's an elastic body simulator," Jacobs says, noting that it's based on a kind of physics solving known as finite-element analysis, which has been a generic approach to simulations since the 1950s.
At Weta Digital, he, Simon Clutterbuck, and Richard Dorling had received a Scientific and Engineering Award in 2013 for Weta's software system called "Tissue," a physically based character simulation framework. Jacobs also received a VES nomination that year for his work on the Goblin King in The Hobbit.
Originally from Toronto, Jacobs moved his family back and forth between North America and New Zealand while he worked on Avatar at Weta, then Thor at Digital Domain, and then again at Weta for Tintin.
The fearsome Griever has a slug-like body and mechanical limbs.
"When I went back to Weta, my wife and kids stayed here, so when the opportunity at Method in Vancouver presented itself, I took it," Jacobs says. "Also, I wanted to do something at a higher level."
Once he arrived in Vancouver, Jacobs began looking for people who could help him develop a new creature simulation system. "I'm a visual effects guy, not a hardcore software developer," he says. "I needed someone who could implement a core software library. We needed to get something into production quickly."
Jacobs found John Lloyd at the University of British Columbia, who had written a biomechanics simulator in the Electrical Engineering department for speech pathology. Lloyd wrote the core software library; Jacobs wrote the Autodesk Maya plug-ins.
The result is a finite-element simulation using invertible elastic elements.
"The linear elastic bit provides an approximation of a material," Jacobs says. "It's good to describe materials that don't undergo massive transformation, so the model works well for visual effects. It's a simple material model, easy to get your head around. The invertible part makes it more robust."
Jacobs explains that before this method was available, when a tetrahedron - the pyramid-shaped bit of geometry used in meshes - is inverted, the solver, that is, the simulation engine, doesn't know how to deal with mesh, so the volume described by the mesh becomes corrupt.
"If the top of that pyramid shape gets squished into a flat plane, or becomes flat, the volume becomes negative or flattened," Jacobs says. "Take a character's arm. If you have tetrahedra in a certain size and the arm moves fast, it might invert. In older approaches, when elements deform in a linear elastic fashion and the movement is more than a certain amount, the element - the arm - could become degenerate. Our solver allows things to become inverted and correct themselves when they can."
As a result, the solver is more forgiving when animators move a CG character in extreme ways. It's also flexible.
"We can use it for generalized elastic bodies, and we can also apply a muscle activation field," Jacobs says. "We can specify a UV direction per element for fields we want to intersect that element. When we apply an activation force, it will cause a single tetrahedron or many to contract in the direction the field is running."
The result is analogous to the way muscle fibers behave. "Muscles are mostly water, so when we squish them, they bulge in transverse ways,"
Jacobs says. "And because our elements conserve volume, when we squish them, they transversely bulge."
CG fire envelops the digital creature, causing it to scream in terror.
Artists working with the system can assign material properties, such as stiffness, density, and volume conservation, to simulate muscle, fat, and tendons, all of which helped add jiggles and wiggles to the organic part of the Griever in The Maze Runner.
"He's meaty and slug-like," Jacobs says. "We gave him a structure like a seal, which is a fat animal with a support structure under the fat. We baked out the animation onto the skeleton and drove the simulation from the skeletal motion. Onto each bone, we attached muscles and fat, and applied constraints - parameters that determine when muscles flex based on some criteria. We don't have tons of muscle detail, but we did get wave propagation that you can see in some shots. He settles, pounces a foot, and you see a shock wave through his body."
The simulator took care of the shock wave using properties the team set.
"We defined him as soft on the inside with a fat layer that was very volume conserving, and outside, he has a thin layer of stiffer material constrained to the underlying anatomy. So, he moves a little like a water balloon. With a water balloon, you squeeze one end and the water fills the other. With the Griever, it's not so direct because we split the volume into hundreds and thousands of tetrahedra."
Running simulations like this always carry a computational cost, though.
"Because of the computational cost, we wanted to parallelize it as much as possible, so I based our system on a Crawford Doran dependence graph," Jacobs says. "Each node on the graph represented a different stage of running the simulation to produce the final simulation. We could specify which nodes happened in parallel."
After the system's successful application on the Griever in The Maze Runner, the developers created a stand-alone tool that includes the solver and Maya plug-in. And, they have expanded the system.
"For The Maze Runner, we ran the system only on the organic part of the Griever," Jacobs says. "Now, the system can represent rigid bodies, as well." -