Crafting the insane action behind ‘Thor: Ragnorak’s’ end battle

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WARNING: Contains some plot spoilers.

Amongst the many and complex visual effects sequences in Taika Waititi’s Thor: Ragnarok, the final battle on Asgard is perhaps the most epic. Here, the evil Hela (Cate Blanchett), her d-guards and massive dog Fenris take on Thor (Chris Hemsworth), Hulk (Mark Ruffalo), Valkyrie (Tessa Thompson), Loki (Tom Hiddleston) and several other characters, including a giant version of the fire demon fire demon Surtur.

It’s a sequence that involved significant fight choreography, CG character animation, enormous destruction and a surprising twist in Thor’s superpowers. Here’s a look at how Framestore, working with overall visual effects supervisor Jake Morrison, pulled off some of the battle’s key moments.

Hulk versus Fenris

Hela’s 35 foot long Fenris – which appears as an oversized dog in the film – engages in a wrestling match with Hulk on the rainbow bridge in Asgard that also moves into the water and on a waterfall. One of the first major challenges was scaling up a CG canine to appear realistic, with Morrison noting that rendering scaled fur can be tricky.

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“If you actually took a normal density of fur that you would have on a dog and standard width of a single hair follicle for a standard dog and then just scaled it up, it would inherently just look terrible and it would at best look like Hela had shrunk, and at worst it would look like the biggest, cheapest CG dog that you’d ever do.”

The answer was to deliver a complex groom and appropriate reference. “We used a lot of references of real wolves, their groom, their facial expression, and how they move,” explains Framestore visual effects supervisor Alexis Wajsbrot. “We also had a real scan of Dickens, the dog used on set, as well as a wolf, which was great information for skeleton proportion.”

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“Regarding the scale challenge,” adds Wajsbrot, “we just made sure they were a lot of variation in her groom, in term of clumping, greasiness, bold patching with scars, and attaching some dirt and small debris to the groom. We also made sure with Jake and Taika that we were always using a low angled camera either at human height level or lower.”

Not only was Framestore crafting a CG Fenris, they also had to deliver a CG Hulk, with specific facial and muscle simulations, for the fight. That the fight takes place in water – simulated with the studio’s proprietary solver called Flush and rendered in Arnold – made things even more complex.

“The camera from Taika was incredibly close to the rapid water and we have two giant creatures creating extra splashes,” says Wajsbrot. “It was really hard to clear the camera but still make it feel like natural water simulation. It was the same for Hulk and Fenris; the first simulations were very quickly obscuring our heroes so it was all about finding the right balance between making the water sim big but still showing the performances.”

Battling d-guards

Hela has awoken an army of dead Asgardian soldiers – d-guards – to bring into battle. On the rainbow bridge they fight Thor, Valkyrie, Hulk and the others. Just staging such a complex scene proved challenging for Framestore given the location.

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“We were constantly coming back to the edit to make sure that first the camera is pointing in the right direction (north / south / west / east),” notes Wajsbrot, “but also making sure it’s in the right position on the bridge – of course any edit changes impacted this layout.”

“We held various mocap sessions. The very first mocap session we did focused a lot more on the animal as the first concept of the Dguards showed them as a lot less human than they ended up being. We then did a first pass blocking animation on every shots matching the intention of the previs. From there we did two new mocap sessions in the Framestore mocap studio, where we specifically directed the shots and made the animation a lot more human. There are of course a lot of hand animation to make it work perfectly for the shot.”

During the battle, a particular song beat begins (Led Zeppelin’s Immigrant Song), which the action needed to match. “Asgardians rarely kill the Dguards,” says Wajsbrot, “we just added sparks on the contact points between sparks. Val’s dagger was able to slice the d-guards, it was a lot of fun to destroy them making sure that we are in the PG-13 bandwidth, not too many organs, bones or blood. Korg and Skurge who both have machines gun were able to shatter them creating holes in their bodies. Then we had Uber Thor (see below); his killing needed more variation, some d-guards just emit debris, some are exploding in mid-air, some are shattering, some are just thrown like ragdolls. We just needed a good amount of variation for the sequence to not look repetitive and be as entertaining as possible. All the destruction simulation was handled in Houdini.”

Uber Thor

Desperate to defeat Hela, but without his hammer, Mjölnir, and blinded in one eye, Thor manages to conjure up lightning and become ‘Uber Thor’. His new-found powers required the articulation of lightning bolts and spurts of energy with a somewhat 1980s feel (Morrison poured over reference from films like Bill and Ted’s Excellent Adventure, Ghostbusters and Big Trouble in Little China).

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Framestore delivered a fully CG Thor in order to obtain the correct light interaction between the lightning bolts and his model. “We modelled, groomed and shaded a very high res version of Chris Hemsworth that could work in both closeup and far away,” says Wajsbrot. “We also created a muscle rig specially for the arms and a cfx rig for cape and costume.”

For most of the shots, Framestore received plates of Thor fighting in a mocap suit on a blue screen. Artists then body tracked Hemsworth even when he would be become a CG character as they would be keeping his face and facial expressions.

“Regarding the lighting bolts themselves,” says Wajsbrot, “we used tesla coil references for the motion, and a Houdini setup where we were able to art-direct the density and the speed of the bolts on him. Thor was also able to emit a lighting bolt to kill d-guards and even call lightning from the sky. The lighting bolt was generated using point clouds, we also generated a volume around to emit light which was less noisy and faster to render for the light interaction on both the environment and Thor. We generated a plasma (smoky) pass that was lit by the bolt to make it more detailed. When we see Uber Thor’s foot contact the bridge we also added some extra 2d bolts inside the rainbow bridge, to show the spark emitted from his foot.”

Giant Surtur

The audience had previously met Surtur right at the beginning of the film, when he is dispatched by Thor. Realizing there is a way to ressurect the creature and destroy Hela – but also Asgard in the process – Thor rebirths Surtur into a giant.

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It was another scale challenge for Morrison and the VFX team. “Having just done Ant-Man was a really good masterclass in scale, because I learnt an awful lot there,” the visual effects supervisor relates. “He’s portraying someone who is basically exactly the same proportions as a normal human but all of a sudden they’re half an inch tall.”

An early request from the director was that Surtur eschew the usual slowed down motion typical of giant characters, usually employed to show weight. “Taika said to us,” Morrison recalls, ‘You know what the one thing we’re bored of in films? When they slow down big things.’ Myself and Framestore visual effects supervisor Kyle McCulloch were both like, ‘Oh, but that’s how you can tell scale!’”

“This was a big challenge for us, as one of the key ways to convey scale in a huge character is how they move relative to the world around them,” notes McCulloch. “From the beginning, the filmmakers were quite attached to their previs, and our animation team dove in on building from those performances, and bringing new ideas to the table on how best to sell the massiveness and gravity of the Titan of Fire.”

Framestore launched into a exploratory phase for the fiery look – matching the speed desired by the filmmakers sometimes had Surtur brandishing his swords at crazy speeds of Mach 40.

“The brief for Surtur included references to the surface of the sun, plasma, lava, and fire,” says McCulloch. “The lookdev team spent months partnering with our shader writers, experimenting with a myriad of ways to have something feel huge, somewhat transparent and refractive, while still seeing a visual complexity and surface. In the end, much of the look of Surtur’s body was a comp-led combination of a set of passes that isolated fresnel elements, refraction, muscle volumes and skeletons, as well as a cracked, lava-flow surface.”

Framestore’s FX team provided various volumes and point clouds for the shading team to drive more complex lighting models. They also developed a library of solar flare like elements that could be dressed in both character space and world space. “Lastly,” states McCulloch, “they built a fire simulation system that could wrap and define Surtur’s body, perform within the space around him, and have the visual scale of detail required to sell how big they were.”

“The other piece to the Surtur shots was the destruction around him,” adds McCulloch. “The FX team provided a diverse library of generic building and structure collapses with related smoke and fire that the environment team could use to dress shots. This was all created and managed with our in-house tool set, fRaze. There were also the specific and hero simulations that related to his actual actions, like sword strikes in the city and destroying the planet. Again – scale was the biggest challenge in this work, and much of our iteration and research went into finding the right pace and speed, as well as scale of detail, for the various elements.”

Surtur causes such mayhem that he also destroys Asgard, but only after many of its citizens have been able to escape. It begins with the creature plunging his sword deep into the crystal heart of the world. Framestore generated a semi-primordial landscape with flames and cracked mountains spewing lava, tidal waves and waves of flames – all at a macroscopic scale, as seen from space.

“We decided it would be nice to have all the water and clouds on Asgard dispersed with a shockwave, so that all went first,” outlines visual effects supervisor Jonathan Fawkner. “We simulated particles to blow the surface water and waterfalls of the disk of Asgard and we used motion vectors to dissipate the matte painted clouds in Nuke. Various shell like energy fields were added and then the master simulation consisted of crystalline and rock geometry, with separately advected fluid and dust passes, all emanating and silhouetted by what is left of the once bright heart of an ancient realm.”