If you've seen G.I. Joe: Retaliation then you've seen all sorts of crazy action - ninjas battling on mountain cliffs, tanks blasting each other and cities being destroyed like glass. We talk to visual effects studios ILM, Digital Domain and Method Studios to find out how they handled the biggest and most kick-ass sequences in the Jon M. Chu-directed film. Plus we have exclusive Digital Domain making of VFX clips.

***Warning: this article contains spoilers***


Nanomite reveal

The action: Zartan (Arnold Vosloo) reveals that he has been impersonating the President of the United States (Jonathan Pryce), which he does by cutting open his skin and showing how microscopic nanomite robots repair the tissue.

Watch Digital Domain's breakdown for the nanomite reveal sequence.

VFX: "The challenge here was that we had to make something that looked mechanical, clearly non-organic and do it very quickly," says Digital Domain visual effects supervisor Thad Beier, who oversaw the effects for the nanomite face reveal under overall VFX supe James Madigan. "The idea was that there's a network of nanomites that build the face, and once he injures himself the nanomites rush over to heal him and then come back and it's that rushing over that reveals him underneath."

At one point, Beier considered doing the shot as a two-and-a-half-D solution, taking each plate and using pieces of them to assemble the final image. "But the director really wanted to be able to art-direct every bit of Zartan's motion after the fact," notes Beier. So DD looked to its head replacement technology developed on Benjamin Button and refined on TRON: Legacy to build a fully digital head for Zartan that could be animated to match the desired final shot. "We did of course have footage of Vosloo's performance from the set so we knew exactly what it should look like, how his coloration and skin texture differed," says Beier.

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CG models of Vosloo and Pryce were modeled based on cyber-scans and photo-reference, complete with sub-surface scattering, peach fuzz and other textures, with blend shapes used to morph between them. Eyes were significant challenges. "You think of any eye as being a ball with color in it," says Beier, "but there's a lot more to it than that, in particular the way the water that covers the eye transitions into a meniscus up against the skin, which is critical to close-up shots of eyes to make them look alive and real." The final shot made use of geometry for Zartan's eyes, unwrapped in UV space, with both pieces of eye footage stablized and a generic blend made to map onto the geometry, in 3D, in Nuke.

In terms of animation, DD initially tried to match Vosloo's gross motion, going from the President's (Pryce's) motion to Vosloo's. "But it was just too jarring," admits Beier. "So we decided we would have Arnold more closely match the President's performance, and at that point everything snapped into place and was a more realistic believable motion."


G.I. Joe camp attack

The action: In a nighttime assault, Apache helicopters lead a Cobra attack on a G.I. Joe desert camp, killing nearly all the Joes.

VFX: Method Studios delivered CG choppers, tracer fire, rockets and rocket trails, and also augmented explosions. In addition, shots of the Apaches on approach required night vision views of the entire encampment, which had to be built in CG.

Watch behind the scenes of the G.I. Joe desert camp shoot.

Production filmed at a gravel pit in St. Francisville, near New Orleans, setting off numerous practical explosions at the site. In fact, two versions of the set were built - one to remain pristine and clean and one to be blown up. To craft the desired helicopter shots, the filmmakers began by piecing together their favourite chopper scenes from film and television shows. "The pacing and staging of the sequence was already mapped out in many ways before they even storyboarded the actual sequence," recounts Method Studios visual effects supervisor Ollie Rankin. "Then they worked from that animatic which was a mixture of previs and live action shots from throughout the history of cinema. There was no continuity necessarily but you've got the germ of an idea of a shot design."

Method modeled and textured an Apache attack helicopter based on collected reference, fitting it out with rocket and missiles. The scenes are at nighttime which meant pilots were not heavily visible, although there were CG digi-doubles in the CG Apaches. Explosions and interactive lighting from the live action shoot served as timing reference for animation of missile hits, with additional pyro and sparks from James Madigan-supervised shoot in LA added to the final shots. "And then we had a Maya fluid rig that worked well for pre-generating a library of missile trails," says Rankin. "We did additional simulation if the helicopter was flying over the rocket trail afterwards since it would need the down draft to disturb and disperse the smoke."


Firefly's fireflies

The action: Ex-Joe Firefly (Ray Stevenson) employs a swarm of explosive CG robotic fireflies to break Cobra Commander (Luke Bracey) from prison. They are revealed as he pulls a canister out of his motorcycle, on which a honeycomb collection of the fireflies come to life, spreading their wings and taking off. Their tails switch on to reveal a glass fluid canister which explodes once they reach their target.

See some of the firefly shots, and others from G.I. Joe: Retaliation in this clip.

VFX: Method modeled hero fireflies "down to the servos that operated the irises of their eyes," explains Ollie Rankin. "Then for shots where there are hundreds of them, we developed a system in Maya - more or less a particle system - but the clever thing about it was rather than just having these particles that followed a particular trajectory we generated motion paths for them. What that meant was if we needed to manipulate the path of any individual firefly or sections of the swarm, it was more easily done than changing any attribute and re-generating it."

In one signature shot of the fireflies, a speed ramp was applied to highlight the flapping of their wings and the subtle movement of their dangling legs. The later firefly explosions were practical elements that Method matched their digital robot animation to. "We had done some R&D initially thinking we'd need to see the fireflies go from intact robots to exploding on camera," says Rankin. "But because of the speed of the explosions, there was very little you could see."


Not your typical motorcycle

The action: Firefly's motorcycle also doubles as a deadly and destructive weapon itself, able to be launched as individual missiles. In one sequence, it transforms and explodes into a bunker.

Watch Digital Domain's breakdown of Firefly's deadly motorcycle.

VFX: A live-action motorcycle and rider were filmed performing the stunt. Digital Domain then built a CG bike and digi-double for a transition as the bike breaks apart - something shown in the final shot in slow motion. "We scanned the real bike with LIDAR, took photos and built a matching model," says DD visual effects supervisor Thad Beier. "Originally, we built little wings that popped out of every piece to help them fly, but the director didn't like that - so they just had rockets to push them through the air."

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DD had to match LEDs that had been used on the practical bike to illuminate engine parts, retaining the illumination as the parts shot through the air. "I also just loved this Firefly character after this shot with all his weapons and everything," comments Beier. "He pops his parachute and comes down to the ground as cool as anything - 'Oh yeah, I do this every day'."


The ninja cliff battle

The action: On a precarious mountain rock face, a group of ninjas, including Snake Eyes (Ray Park) and Jinx (Elodie Yung), take on their adversaries. The sequence required swinging, zip-lining and close-quarters martial arts on the cliff face near a mountain monastery.

Watch part of the cliff battle.

VFX: ILM handled visual effects for the sequence, taking live action plates and greenscreen photography and filling out the mountain environment, as well as replicating some ninja action with digi-doubles. Initial background plates and reference imagery were acquired at Butte Mountain, in British Columbia via both helicopter and platform access. Later, actors and stunties performed daring moves against a giant greenscreen and set constructed with stunt rigging at NASA's Michoud Assembly Facility in Louisiana, once used to build fuel tanks for the Space Shuttle.

Ray Park plays Snake Eyes (left) against Ninjas in the cliff battle.
Ray Park plays Snake Eyes (left) against Ninjas in the cliff battle.

Much of the action took place on a near-vertical wall, something ILM visual effects supervisor Bill George recognized would result in fighting occurring in shadow. "Technically that's great on a sound stage because you don't have to worry too much about shadows and rigging," he says, "but ultimately it gives you very flat light. We had to then create an environment that reflected that reality of being in the shadow, but remind people that right outside the area it's bright and sunny and covered in snow."

The mountainous terrain and rock walls were photo-modeled from reference, with extra details helping to sell the vastness of the shots. "The ninjas would kick up snow and rocks and leave little sparks on the wall," notes George. "We would add light contamination or mist as you're looking down. The idea that you're looking down from the characters and seeing clouds, makes it look high - which was the goal. Not only was it a ninja battle but they're frickin' way up in the sky hanging from these little ropes!"

Watch behind the scenes of the greenscreen shoot for the cliff battle.

For shots requiring digital ninjas, George says it was almost the 'perfect scenario', since there was little hair and flesh to sim because of the form fitting and full-body suits. "Sometimes, though, we needed to do a completely digital character and other times we had to change say just Jinx's swing with her sword and make it more aggressive, so we had to blend in our CG arm to her real arm," he says.

Another challenge for the CG doubles was replicating the incredible bounding actions - moves that the performers had actually staged on the greenscreen set. "The thing is," explains George, "if you did a giant leap you would just start spinning end over end. So, just as when you drop a cat and it swings its tail like a gyroscope to stay stable, the guys, when they would jump off a wall, they would pretend to be riding a bike with their legs and it would keep them stable but it looked so comical. So we had to replace that in parts."

Ray Park plays Snake Eyes (far left) against Ninjas in the cliff battle.
Ray Park plays Snake Eyes (far left) against Ninjas in the cliff battle.

London is destroyed

The action: Cobra makes a definitive display of his intentions by launching an attack on London via Project Zeus - several orbital kinetic bombardment weapons of mass destruction. One fires a piece of platinum, essentially a man-made meteor, into the center of the city, causing structures and surroundings to shatter with a ripple-like effect.


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VFX: "We started working on the concept of what that looks like - everyone's seen explosions - we wanted to do something different," says ILM's Bill George. "The concept we came up with was that it was like shattering glass, great concentric rings like a spider web so when it breaks it's like when a bullet goes through glass. The same thing happens to the surface of the earth."

"I said to Paul Kavanagh, our animation director, that I'd really like to keyframe the foreground pieces to have their timing and motion be exactly what we want, especially for the Thames, which we wanted to tilt forward to see the water sheeting off," adds George.

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ILM artists created the ground plane based on aerial stock footage reference, then using a combination of keyframe animation and simulations broke up the surface. "Once we got the plates the way we liked it we got the buildings and the sims would fall where they may," explains George. "Things close to camera, like the Parliament buildings, were hero assets and then the other background buildings were handled by Digimatte as objects in lower res, but were still simulated."


Tank v Tank

The action: Roadblock (Dwayne Johnson) takes on Cobra Commander’s three HISS tanks in his own mini-tank.

Watch Digital Domain's breakdown for the tank sequence.

VFX: Digital Domain and Reliance in London collaborated on CG tanks for the sequence, referencing a real, working tank built by special effects coordinator Michael Meinardus. This was LIDAR-scanned and extensively photographed. HDRs for every shot in the tank battle were also captured.

"The biggest challenge for us," says DD visual effects supervisor Thad Beier, "was when a tank was burning or blown up. Typically an HDR shows all the light coming in from infinity but when the tank is enveloped on fire the light is all over the place, you're inside the light source."

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Another challenge was for moving shots of the tanks which had to reflect the mud and dirt being picked up in their treads - done with sims. "Even the tracer fire was difficult - you think this would have been solved 15 years ago," says Beier, "but tracers during the day don't really show up in real life, and you don't often see tracers whizzing by. To make it visible and coherent and not seem too slow that it was ridiculous required a lot of revisions."


ICBM and Zeus satellite explosions

The action: Deceived by Zartan, several nations of the world fire their Intercontinental Ballistic Missiles (ICBMs) at once. But Zartan demonstrates his power by blowing them all up in space. Later, for the film's finale, the Zeus WMD satellites are also destroyed.

VFX: Digital Domain created an explosion featuring the biggest sim the studio had ever done. Reference came from MX Peacekeeper missile explosion footage, which looked like millions of pieces of burning debris. FX lead Jeremy Hampton handled the sim. "Houdini DOPS gas solvers were used," he says. "We initially tested the idea of using sim clustering on these explosions (one simulation for each rocket stage ) but ran into issues along the boundaries where the sim would need to transfer from one bounding volume to the next. I created a stripped-down version of the native pyro solver that would run the sims more efficiently, and we ran one long simulation for the explosion that topped one billion voxels."

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"Houdini allowed us to have control over the amount of divergence in a combustion sim and has some very good tools for shaping volumes, which generates very nice results with fast expanding explosions," adds Hampton. "As well, Mantra is a fantastic renderer for volumes. Trying to motion blur billions of voxels is not an easy task for any renderer, especially when they are directly filling the camera frustum."

Hampton also took on the Zeus satellite explosion shots. Reliance modeled a complicated satellite, while DD explored how an explosion in space should appear. "Research shows it's an almost instantaneous flash of light and the reaction disappears," says DD visual effects supervisor Thad Beier, "but that won't work for a movie. We came up with a plan where you'd see the burning and rushing away - the gases from that destroy the satellite - and we made it bright blue." DD used its Drop RBD system (based on the Bullet engine) to sim the satellite destruction in conjunction with Houdini.


Images courtesy Paramount Pictures, ILM and Digital Domain. All images and clips copyright © 2013 Paramount Pictures. All Rights Reserved. Hasbro and its logo, G.I. JOE and all related characters are Trademarks of Hasbro and used with permission. All Rights Reserved.


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